N-(2-ethylhexyl)-8,9,10-trinorborn-5-ene-2,3-dicarboximide

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1992

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

absorption

distribution

excretion

Principles of method if other than guideline:

Since the major route of human exposure is dermal, this study was designed to obtain information on the
pharmacokinetic and distribution parameters of MGK 264 following multiple dermal administrations in the rat.

GLP compliance:

yes

Radiolabelling:

yes

Species:

rat

Strain:

other: CRL:CD Br

Details on species / strain selection:

The rat is a species commonly used for pharmacokinetic
studies and is the animal of choice for this study according to
the EPA Pesticide Assessment Guidelines. In addition, a number of
other toxicological evaluations have been and/or are scheduled to be
conducted on MGK 264 utilizing this strain of rat as the test animal

Sex:

male/female

Details on test animals or test system and environmental conditions:

All experiments were performed on adult male and female Charles River CD
(CRL:CD Br) rats obtained from Charles River Breeding Laboratories, Portage,
Michigan. The rats were approximately six weeks of age when received by the BTC.
Upon arrival, the test animals were transferred to a quarantine room where they were
eartagged and maintained in individual, hanging, stainless steel cages throughout the
two week quarantine period. Soon after their arrival, the animals were examined for
general health by the staff veterinarian. The animals were weighed once each week
during the quarantine period. During the second week of quarantine, the animals
were weighed and their food consumption was monitored. Animals that showed poor
food consumption or poor weight gain during quarantine were eliminated from the
study. Morning and afternoon mortality checks were conducted each day during the
quarantine and testing periods. Prior to dosing, all animals were re-examined to
assure normal health, moved to the test room and assigned to treatment groups using
a weight stratified randomization procedure.
The animals were fasted for an eighteen hour period prior to the initial
nonradiolabeled dose and six hours post-dosing as well as an eighteen hour period
prior to the radiolabeled dosing and a six hour period post-dosing. Otherwise, the
animals received Purina Rodent Chow No. 5002 ad libitum. Water was provided ad
libitum throughout the quarantine and study periods. No known contaminants were
present in the diet or water which would affect the outcome of the study. Therefore,
no additional analyses outside those completed by the manufacturer and the local
water district were performed.
The room temperature ranged between 69°F-74°F; the relative humidity ranged
between 56%-79% during the quarantine and study periods. A 12 hour light,
12 hour dark cycle was established and the air exchange rate was at least seven per
hour.

Route of administration:

dermal

Vehicle:

other: isopropyl alcohol

Details on exposure:

The nonradiolabeled dose was applied evenly over the application area using a
precalibrated 100 μL glass wiretrol micropipette. The radiolabeled dose was also
applied evenly to the application area within the glass enclosure (backpack). All
doses were administered on a constant volume basis i.e., 100 μL of dosing solution.
The actual amount of dosing solution applied was measured by weight as a
differential between the weight of the micropipette before and after dosing. After the
radiolabeled dosing, a nonocclusive plastic cover was glued to cover the top of the
backpack. Each backpack was checked daily and reglued if necessary.

Duration and frequency of treatment / exposure:

This study consisted of two experiments conducted in rats. The first experiment involved the determination of the blood concentration of radioactivity with time, the determination of peak blood level and half-life of radioactivity in blood, following multiple dermal administration of nonradiolabeled MGK 264 for fourteen consecutive days followed by a single dermal administration of [Hexyl-l-14C] MGK 264 on day 15. The second experiment involved the euthanasia of animals at peak blood level of radioactivity, first and second half-life of radioactivity and at 168 hours following the same dosing regimen.

Dose / conc.:

12 mg/kg bw/day (nominal)

Remarks:

All male rats on both experiments.

Dose / conc.:

17 mg/kg bw/day (nominal)

Remarks:

Female rats only (experiment 2 only)

No. of animals per sex per dose / concentration:

FIrst experiment - 5 male rats
Second experiment - 4 groups of 5 male rats and one group of female rats

Control animals:

no

Positive control reference chemical:

not specified.

Details on study design:

This study consisted of two experiments conducted in rats. The first experiment involved
the determination of the blood concentration of radioactivity with time, the determination of
peak blood level and half-life of radioactivity in blood for male rats. The second experiment
involved the determinations of the amount of compound remaining on the skin and in various
tissues and excreta at peak blood level, at blood half-life and second blood half-life of
radioactivity in male rats and at 168-hours in male and female rats following multiple dermal
administrations of MGK 264 for fourteen days followed by a single dermal administration
of [Hexyl-l-14C] MGK 264 (Endo/Exo Mixture).

In the first experiment, five male rats were administered a daily dose of 100 μL of an isopropyl
alcohol solution containing 5 % (w/w) of nonradiolabeled MGK 264 for fourteen consecutive days.
On day 15, each rat was administered a single dermal dose of 100 μL of 5% w/w [Hexyl-l-14C]
MGK 264 in isopropyl alcohol. Each rat received approximately 12 mg/kg body weight and between
13.9-14.5 μCi of radioactivity. The rats were fasted for approximately 18 hours prior to the first
day of dosing with the nonradiolabeled solution and prior to the administration of the radiolabeled
solution. Following the radiolabeled dose, blood samples were collected from the tail vein at
different time intervals over a 120 hour period and the radioactivity in blood was determined. Blood
radioactivity was very low at all time intervals (2 to 3 times background) suggesting that the
absorption of radioactivity was extremely slow. Two radioactive peaks were present in blood, one
at six hours post-dose administration and one at ten hours post-dose administration. The half-life of
blood radioactivity was calculated to be 28.5 hours. Since these results were very close to the peak
(12 hours) and half-life (31 hours) determined in the single dermal dose study, the decision was made
to use the same time of euthanasia from the single dermal dose, so that data from the two regimens
could be compared.
In the second experiment, four groups of five male rats and one group of five female rats were
administered multiple dermal doses of MGK 264 as described for the blood kinetics study followed by a single dermal dose of [Hexyl-l-14C] MGK 264 at approximately 12 mg/kg body weight for the
males and 17 mg/kg body weight for the females. Each rat was administered between 13. 9-14. 2 μCi
of radioactivity. Based on the blood kinetic data, one group of five males was euthanized at each
of the following time intervals; peak blood level ofradioactivity (12 hours); blood half-life (43 hours)
and second blood half-life of radioactivity (74 hours); and 168-hours post-dose administration. The
group of five females was euthanized at 168-hours post-dose. Urine and feces were collected for
all groups at predetermined time intervals until the time of euthanasia. When the rats were
euthanized, the treated skin and enclosures were removed and rinsed, the animals were then
necropsied and selected tissues and organs were harvested. Samples of urine, feces, tissues, skin
rinse and enclosure rinse were subsequently analyzed for radioactivity.

Details on dosing and sampling:

Experiment 1:
Approximately 22 hours prior to the first day of dosing with the nonradiolabeled test
article, the back and shoulders of five rats were shaved and cleansed with acetone.
The food was removed approximately 18 hours prior to the initial dose and returned
to the rats six hours after dosing. The animals were administered approximately
100 μL of the nonradiolabeled test article to the shaved area of the back using a
100 μL Wiretrol micropipette (Drummond Scientific, Broomall, PA), for fourteen
consecutive days. The nonradiolabeled MGK 264 was administered as a 5 % (w/w)
solution in isopropanol. On day 14 ( prior to the final nonradiolabeled dose, each rat
was anesthetized with Ketamine/Xylazine (7: 1 v/v) and the back and shoulders were
shaved and cleansed with acetone. Care was taken not to abrade the skin. After
shaving, a glass contoured rectangular enclosure (2.5 cm x 5 cm; maximum height,
1.3 cm) was glued onto the middle of the shaven area on each animal's back with a
cyanoacrylate glue (Super Glue). Silicone medical adhesive, Type A, was applied
as a seal around the outside of each enclosure. Each rat was administered the day 14
dose and returned to its cage. Food was removed 18 hours prior to dosing with
14C-MGK 264.On day 15, each rat was administered approximately 100 μL of the radiolabeled
dosing solution to the skin within the enclosure using a 100 μL Wiretrol micropipette
(Drummond Scientific, Broomall, PA). After dosing, a plastic cover with holes to
provide for a nonocclusive cover was glued to the top of the rectangular enclosure
to prevent disturbance of the application site and to prevent mechanical loss of the
test material. The animals were transferred to hanging, stainless steel cages and
placed in individual rat restrainers for blood sampling. Blood samples (100 μL) were
collected from the tail vein at 15, 30 and 60 minutes; 2, 3, 4, 5, 6, 8, 10, 12, 24,
36, 48, 72, 96 and 120 hours. The rats were allowed water ad libitum throughout
the study and food ad libitum six hours after dosing. After the 120-hour blood
collection, the animals were euthanized by C02 asphyxiation and discarded as
radioactive waste.

Preliminary studies:

Experiment 1 results: Two radioactive peaks were present in blood, one at six hours post-dose administration and one at ten hours post-dose administration. The half-life of blood radioactivity was calculated to be 28.5 hours. As both results were close to peak (12 hours) and half-life (31 hours) determined in the single dermal dose study, same time of euthanasia from single dermal dose study will be used for experiemnt 2.

Details on absorption:

For the animals euthanized at peak blood level of radioactivity, a majority of the administered radioactivity (71. 85 % ) was recovered in the skin rinse. For the animals euthanized at blood half-life and second blood half-life of radioactivity, the mean percentages of dosed radioactivity in the skin rinse were 49. 54 % and 3 7 .54 % , respectively. For the males and females euthanized at 168-hours, the mean percentages of dosed radioactivity in the skin rinse were 8.09% and 0.44%, respectively. The dosed radioactivity was slowly absorbed from the skin.
A comparison of the 14C-MGK 264 derived blood radioactivity following a single or multiple dose was considered. The blood levels of radioactivity peaked twice in each dosing regimen and the half-lives were similar. These data demonstrated that there was little or no difference in the blood level of radioactivity or half-life of radioactivity between the two dosing regimens.

Details on distribution in tissues:

Mean % applied radioacivity (>0.11% AR):
peak blood level of radioactivity (12 hours) - 7.3% AR in intestines; 2.2% in carcass 0.5% AR in liver
blood half-life (43 hours) - 6.6% AR in intestines; 1.7% in carcass 0.4% AR in liver
second blood half-life of radioactivity (74 hours) - 5.4% AR in intestines; 1.0% in carcass 0.3% AR in liver
168-hours post-dose administration in male rates- 1.2% AR in intestines; 0.8% in carcass 0.1% AR in liver
168-hours post-dose administration in female rates- 0.3% AR in intestines; 0.6% in carcass

Details on excretion:

Mean % applied radioacivity:
peak blood level of radioactivity (12 hours) - 71.9% AR recovered from urine/ 0.2% AR recovered from feces
blood half-life (43 hours) - 25.7% AR recovered from urine/ 11.1% AR recovered from feces
second blood half-life of radioactivity (74 hours) - 33.2% AR recovered from urine/ 16.5% AR recovered from feces
168-hours post-dose administration Male rats - 51.5% AR recovered urine/ 30.4% AR recovered from feces
168-hours post-dose administration female rats - 69.3% AR recovered urine/ 27.6% AR recovered from feces

Conclusions:

For the animals euthanized at peak blood level of radioactivity, a majority of the administered radioactivity (71. 85 % ) was recovered in the skin rinse. For the animals euthanized at blood half-life and second blood half-life of radioactivity, the mean percentages of dosed radioactivity in the skin rinse were 49. 54 % and 3 7 .54 % , respectively. For the males and females euthanized at 168-hours, the mean percentages of dosed radioactivity in the skin rinse were 8.09% and 0.44%, respectively. The dosed radioactivity was slowly absorbed from the skin. By 168 hours, a majority of the administered radioactivity was excreted through the urine (51.48% for the males, 69.29% for the females) with a significant amount of radioactivity recovered from the feces (30.37% for the males, 27.65% for the females). This indicated that biliary excretion played an important role in the elimination of radioactivity from the body.
The radioactivity recovered from the carcass decreased with time indicating that no accumulation of radioactivity in the body occurred. In general, mean tissue radioactivity decreased with time and did not accumulate in the tissues studied. The total mean percent of administered dose recovered in the four groups ranged between 99.40% - 104.96%. A comparison of the results of the single dose and multiple dose studies indicated that, with the exception of a higher amount of radioactivity present in the skin at the different euthanasia time intervals, following the multiple dose administration, the patterns of absorption, tissue distribution and elimination between the single and multiple doses are comparable.


In conclusion, with the exception of the higher amount of radioactivity present in the skin at the different euthanasia time intervals, following multiple dose administration, the patterns of absorption, tissue distribution and elimination between the single and multiple doses are comparable.

Executive summary:

This study consisted of two experiments conducted in rats. The first experiment involved the determination of the blood concentration of radioactivity with time, the determination of peak blood level and half-life of radioactivity in blood, following multiple dermal administration of non-radiolabeled MGK 264 for fourteen consecutive days followed by a single dermal administration of [Hexyl-l-14C] MGK 264 on day 15. The second experiment involved the euthanasia of animals at peak blood level of radioactivity, first and second half-life of radioactivity and at 168 hours following the same dosing regimen. The purpose of the second study was to determine the tissue distribution, rate and route of excretion and balance of radioactivity at the time of euthanasia. Prior to the initiation of this study, an identical study was performed with the exception that a single dermal dose of 14C-MGK 264 was applied (BTC Study No. P02072). The comparison of the blood concentration of radioactivity with time and the tissue distribution and excretion between the single and multiple dermal doses are presented in this report. In the first experiment, five male rats were administered a daily dose of 100 μL of an isopropyl alcohol solution containing 5 % (w/w) of nonradiolabeled MGK 264 for fourteen consecutive days. On day 15, each rat was administered a single dermal dose of 100 μL of 5% w/w [Hexyl-l-14C] MGK 264 in isopropyl alcohol. Each rat received approximately 12 mg/kg body weight and between 13.9-14.5 μCi of radioactivity. The rats were fasted for approximately 18 hours prior to the first day of dosing with the non-radiolabeled solution and prior to the administration of the radiolabelled solution. Following the radiolabelled dose, blood samples were collected from the tail vein at different time intervals over a 120 hour period and the radioactivity in blood was determined. Blood radioactivity was very low at all time intervals (2 to 3 times background) suggesting that the absorption of radioactivity was extremely slow. Two radioactive peaks were present in blood, one at six hours post-dose administration and one at ten hours post-dose administration. The half-life of blood radioactivity was calculated to be 28.5 hours. Since these results were very close to the peak (12 hours) and half-life (31 hours) determined in the single dermal dose study, the decision was made to use the same time of euthanasia from the single dermal dose, so that data from the two regimens could be compared. In the second experiment, four groups of five male rats and one group of five female rats were administered multiple dermal doses of MGK 264 as described for the blood kinetics study followed by a single dermal dose of [Hexyl-l-14C] MGK 264 at approximately 12 mg/kg body weight for the males and 17 mg/kg body weight for the females. Each rat was administered between 13. 9-14. 2 μCi of radioactivity. Based on the blood kinetic data, one group of five males was euthanized at each of the following time intervals; peak blood level of radioactivity (12 hours); blood half-life (43 hours) and second blood half-life of radioactivity (74 hours); and 168-hours post-dose administration. The group of five females was euthanized at 168-hours post-dose. Urine and feces were collected for all groups at predetermined time intervals until the time of euthanasia. When the rats were euthanized, the treated skin and enclosures were removed and rinsed, the animals were then necropsied and selected tissues and organs were harvested. Samples of urine, feces, tissues, skin rinse and enclosure rinse were subsequently analyzed for radioactivity. For the animals euthanized at peak blood level of radioactivity, a majority of the administered radioactivity (71. 85 % ) was recovered in the skin rinse. For the animals euthanized at blood half-life and second blood half-life of radioactivity, the mean percentages of dosed radioactivity in the skin rinse were 49. 54 % and 3 7 .54 % , respectively. For the males and females euthanized at 168-hours, the mean percentages of dosed radioactivity in the skin rinse were 8.09% and 0.44%, respectively. The dosed radioactivity was slowly absorbed from the skin. By 168 hours, a majority of the administered radioactivity was excreted through the urine (51.48% for the males, 69.29% for the females) with a significant amount of radioactivity recovered from the feces (30.37% for the males, 27.65% for the females). This indicated that biliary excretion played an important role in the elimination of radioactivity from the body.

The radioactivity recovered from the carcass decreased with time indicating that no accumulation of radioactivity in the body occurred. In general, mean tissue radioactivity decreased with time and did not accumulate in the tissues studied. The total mean percent of administered dose recovered in the four groups ranged between 99.40% - 104.96%. A comparison of the results of the single dose and multiple dose studies indicated that, with the exception of a higher amount of radioactivity present in the skin at the different euthanasia time intervals, following the multiple dose administration, the patterns of absorption, tissue distribution and elimination between the single and multiple doses are comparable.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991-1993

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPP 85-1 (Metabolism and Pharmacokinetics)

GLP compliance:

yes

Specific details on test material used for the study:

[Hexyl-l-14C] MGK 264

Radiolabelling:

yes

Species:

rat

Strain:

other: Charles River CD

Sex:

male/female

Details on test animals or test system and environmental conditions:

The animals were four weeks old at the time of arrival at the BTC. The test animals were transferred to a quarantine
room where they were ear tagged, moved to individual cages, examined and found to be free of any observable symptoms of systemic disease. All
animals were kept in individual metal cages and received Purina Rodent Chow #5002 (Purina Mills, Inc., St. Louis, MO) and water ad libitum for a
period of two weeks prior to dosing. The room temperature was recorded to be 62-72 °F; the relative humidity range was
30%-68%. A 12 hour light and dark cycle with at least seven air exchanges per hour was maintained throughout the study.

Route of administration:

oral: gavage

Vehicle:

corn oil

Duration and frequency of treatment / exposure:

4 groups.
1) Blood level Experiment at 100mg/kg
2) Single low dose at 100mg/kg
3) Single high dose at 1000mg/kg
4) multiple low doses at 100mg/kg

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

single low dose of [14C-Hexyl]-MGK264

Dose / conc.:

1 000 mg/kg bw/day (nominal)

Remarks:

single high dose of [14C-Hexyl]-MGK264

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

single low dose (100mg/kg) of non-radiolabelled MGK264 each day for 14 days followed by single low dose (100mg/kg) of [14C-Hexyl]-MGK264 on Day 15

No. of animals per sex per dose / concentration:

5 males and 5 males per group (stated in 'duration and frequency of treatment/exposure'

Control animals:

no

Details on study design:

Four experiments were conducted as part of this study which involved the determination of
the ADME* patterns following the administration of [Hexyl-l-14C] MGK 264 at a single oral low
dose, a multiple oral low dose, a single oral high dose, and a blood kinetics analysis at a
single oral low dose .
*M (metabolsim) details added from Report addendum

Details on dosing and sampling:

Dosing solutions were prepared by placing a weighed amount of nonradiolabeled MGK 264 into a glass vial. An appropriate amount of [Hexyl-l-14C] MGK 264(endo-exo mixture) and corn oil was then added to the nonradiolabeled MGK 264 immediately prior to dosing. The calculations and specific activity of the dosing solutions for the different experiments are presented in Appendix 4. The dose was
delivered by gavage with an intubation needle and a disposable syringe. All doses were administered on a constant volume basis (i.e., 5.0 mL of dosing solution per kg of body weight). The actual amount of compound administered was measured by weight as a differential between the weight of syringe before and after dosing. All doses were administered in terms of actual MGK 264 content .
Urine, feces and urine/feces separator washing samples were collected at the following time intervals: 0-4, 4-8, 8-12, 12-24, 24-36, 36-48, 48-72, 72-96, 96-120, 120-144 and 144-168 hours.At the end of the study, the cages were rinsed with distilled water and the weight of water was determined.Seven days after the radiolabeled dose, the animals were anesthetized and euthanized by exsanguination following heart puncture.The following tissues and organs were harvested, rinsed with normal saline and assayed for radioactivity: bone; brain; fat; gonads (testes, seminal vesicles, prostate, ovaries, uterus); heart;kidneys; intestine; skin (nape of neck, washed and shaven); hair; stomach; liver; lungs; blood; muscle; spleen; pancreas; any tissues which displayed pathology and residual carcass. Fat and muscle samples were taken as
composite to represent the total fat and muscle burden.

Statistics:

The mean (i) and the standard deviation (SD) were used to characterize the data (i.e.,
radioactivity measurement, concentration, etc.).

Preliminary studies:

The half-life of blood radioactivity for the males and females was calculated using the Lotus 1-2-3 data
regression program and found to be - 8 hours and - 6 hours, respectively .

Type:

absorption

Results:

MGK 264 is rapidly absorbed with peak radioactivity in the plasma see at 4 hours post dose in males and 6 hours post dose in the females.

Type:

distribution

Results:

MGK 264 was widely distributed in the tissues after a single or multiple oral doses. Residual 1 4C in tissues of all groups was negligible after oral administration of [Hexyl-l-14C] MGK 264 .

Type:

excretion

Results:

49.49% - 73.05% of the recovered radioactivity was found in the urine and 20.87% - 46.67% in the feces.

Type:

metabolism

Results:

MGK 264 was extensively metabolized prior to its elimination; only 1.83 % to 5.27% of administered dose excreted unmetabolized. The metabolic profile revealed that the 14C residues were distributed among four major and several minor metabolites.

Details on absorption:

MGK 264 is very quickly adsorbed. Blood levels of radioactivity for male rats peaked after - 4 hours and for females - 6 hours post dose. The blood half-life was calculated to be - 6 hours for females and - 8 hours for males .

Details on distribution in tissues:

After oral administration of MGK 264 it was seen to be widely distributed in heart, liver, lung, kidney, skin, stomach, intestine, pancreas, muscle, testes, hair, bone. spleen, fat, prostate, seminal vesicles and blood.

Single Oral Low Dose Administration: tissue residues were similar in males and females with the exception of the liver, intestines, hair and the carcass. The males retained more radioactivity (ppm) in these organs than the females.The total residues in tissue and carcass ranged between 0.00% and 0.70% of dosed radioactivity for all rats studied.

Multiple Oral Low Dose Administration: tissue residues were similar in males and females with the exception of the liver, intestines, hair and carcass. The females retained more radioactivity (ppm) in these organs than the males. The total residues in tissue and carcass ranged from 0.00% and 0.55% of dosed radioactivity for all rats studied.

Single Oral High Dose Administration: tissue residues were similar in males and females with the exception of the liver, intestines, and fat. The males retained more radioactivity (ppm) in these tissues than the females. The total residues in tissue and carcass ranged between 0.10% and 0.49% of dosed radioactivity for all rats studied.

Details on excretion:

Single Oral Low Dose Administration:
MALE - A mean of 94.64% of dosed radioactivity was recovered in the urine and feces.
FEMALE - A mean of 97.30% of dosed radioactivity was recovered in the urine and feces.
Multiple Oral Low Dose Administration:
MALE - A mean of 96.86 % of dosed radioactivity was recovered in the urine and feces.
FEMALE - A mean of 93.92 % of dosed radioactivity was recovered in the urine and feces.
Single Oral High Dose Administration:
MALE - A mean of 95.25% of dosed radioactivity was recovered in the urine and feces.
FEMALE - A mean of 92.85% of dosed radioactivity was recovered in the urine and feces.

Metabolites identified:

yes

Details on metabolites:

Four major metabolites observed A,B,C and D. A and B are isomers of each other and C and D are isomers of each other.
All four metabolites found in Male and Female rates but quantities differed.
The HPLC analysis of urine and feces from rats in the ADE phase of the study showed [Hexyl-1-14C]MGK 264 was extensively metabolized prior to its elimination with only 1.8 % to 5.3% of the administered dose excreted as unmetabolized MGK 264.
The percent of administered dose excreted as Metabolite C and D in urine and feces was higher in females (44.7%-59.3%) than in males (30.9%-37.0%).
The percent of administered dose excreted as Metabolite A and B in urine and feces was higher in males (53.6% -62.4%) than in males (34.8%-42.8%).

The metabolism phase of this study was undertaken in two steps. First, additional male and female rats were orally dosed with [Norbornene-2,3-14C] MGK 264 at the high-dose level (approximately 1000 mg/kg) used in the ADE study. Excreta was collected from these animals in order to obtain a sufficient mass of 14C residues for metabolite isolation, purification and identification. Following
preliminary extraction and clean-up procedures, the 14C residues in urine were isolated and purified using high pressure liquid chromatography (HPLC) and identified by thermospray liquid chromatography mass spectrometry (LC/MS) and particle beam mass spectrometry (LC/EIMS) and gas chromatography/mass spectrometry (GC/MS). The second step involved the determination of the metabolic profile by HPLC and quantitation of the 14C residues in excreta samples obtained from animals in the ADE study. ADE study urine and fecal samples representing over 85 % of the excreted radioactivity were composited by sex and dose group. The urine composites were analyzed directly by HPLC whereas the fecal composites were extracted with water and methanol and the extracts analyzed. The peaks on the resulting chromatograms were matched with the identified metabolites and quantitated.
Four major peaks were isolated from urine by HPLC and characterized by mass spectrometry. The first metabolite (identified as Metabolite A) was formed by l3-oxidation of the side chain to produce a carboxylic acid and oxidation of the norbornene ring double bond to produce an epoxide. The second metabolite (identified as Metabolite B) had the same fragmentation pattern as Metabolite A and is an isomer of Metabolite A. The third metabolite (identified as Metabolite C) was formed by w-l oxidation of the side chain to produce a carboxylic acid and oxidation of the norbornene ring double bond to produce an epoxide. The fourth metabolite (identified as Metabolite D) showed a similar fragmentation pattern to Metabolite C and is an isomer of Metabolite C. The GC/MS indicated that peak four also contained a minor metabolite which coeluted with Metabolite D. The mass spectra indicated it was the product of beta-oxidation of the side chain with the norbornene ring remaining intact and unchanged. The structure of MGK 264 and its major metabolites are shown in the final report attached to this end point record.
The HPLC analysis of urine and feces from rats in the ADE phase of the study showed [Norbornene-2,3-14C] MGK 264 was extensively metabolized prior to its elimination. MGK 264 was not detected in the urine and only 0.07%-2.57% of the administered dose was excreted in the feces as unmetabolized MGK 264. The percent of administered dose excreted as less polar metabolites (Metabolite C, Metabolite D and Zone 4) in the urine was higher in the females (45.96%-52.43%) than in the males (19.98%-33.92%). Further, the percent of administered dose excreted as polar metabolites (i.e., Metabolite A, Metabolite B, Zone 1, Unknown 1) in feces was higher in males (26.35%-3l.05%) than in females (12.57%-14.48%) indicating a sex difference in the quantitative metabolism of MGK 264.

Conclusions:

ADME conclusion - following administration, [Hexyl-l-14C] MGK 264 is very quickly absorbed (oral doses) with peak plasma levels detected at 4 hours in males and 6 hours in females. The half-life of radioactivity in the blood was found to be 8 hours in males and 6 hours in females. The total percentage absorption following an oral administration of MGK 264 was not reported. MGK 264 is extensively metabolized prior to its elimination with only 1.83 % to 5.27% of the administered dose excreted as unmetabolized MGK 264. Excretion is rapid and is predominantly in the urine and faeces, with very little tissue accumulation. The HPLC analysis of urine and faeces from rats in the ADE phase of the study showed the percent of administered dose excreted as less polar metabolites in urine and faeces was higher in females (44.72%-59.34%) than in males (30.93%-37.03%). Conversely, the percent of administered dose excreted as polar metabolites in urine and faeces was higher in males (53.60%-62.41 %) than in females (34.79%-42.75%) indicating a sex difference in the quantitative metabolism of MGK 264.

Executive summary:

Four experiments were conducted as part of this study (BTC Study No. PO1932, Selim, S. 1992 and BTC Study No PO1932 Addendum, Selim, S. 1993). The experiments involved the determination of the absorption, distribution, metabolism and excretion (ADME) patterns following the administration of [Hexyl-l-14C] MGK 264 at a single oral low dose, a single oral high dose, and a multiple oral low dose. In addition, rat blood kinetics were determined following a single oral low dose administration. Ten rats(5males and5females) were used in each of the four experiments. The rats were fasted for approximately 18 hours prior to the administration of the [Hexyl-l-14C] MGK 264. Each animal was administered approximately 18-30μCiof radioactivity. With the exception of the single high oral dose, 100 mg/kg of [Hexyl-l-14C] MGK 264 was administered. In the single high oral dose, 1000 mg/kg [Hexyl-l-14C] MGK 264 was administered. Rats in the multiple oral low dose experiment were given a daily oral low dose of 100 mg/kg of the non-labeled compound by gavage for two weeks followed by a single oral low dose of the labeled compound. Urine and feces were collected for all groups at predetermined intervals. Seven days after dose administration, the rats were euthanized and selected tissues and organs were harvested. Samples of urine, feces and tissues were subsequently analyzed for 14C content.

In the blood kinetics study, radioactivity peaked at approximately 4 hours for males and 6 hours for females. In all of the definitive experiments, 49.49% - 73.05% of the recovered radioactivity was found in the urine and 20.87% - 46.67% in the feces. Tissue residues of 14C were less than 0.43% of the administered dose in all groups. The total mean recovered radioactivity of the administered dose in the three groups ranged between 93.13% - 97.43%.

Metabolism and identification of metabolites was investigated by the quantitation of the 14C residues in the excreta of rats orally administered [Hexyl-l-14C] MGK 264. Three oral dosage regimens were evaluated. These included: a single oral low-dose (I 00 mg/kg), a single oral high-dose (1,000 mg/kg) and a multiple oral low-dose (animal preconditioned with 100 mg/kg of nonradiolabeled MGK 264 for 14 days followed by a 100 mg/kg dose of [Hexyl-l-14C] MGK 264 on day 15). The metabolism phase of this study was undertaken in two steps. First, additional male and female rats were orally dosed with [Hexyl-V4C] MGK 264 at 859 mg/kg and 697 mg/kg, respectively. Urine and feces were collected from these animals in order to obtain a sufficient mass of 14C residues for metabolite isolation, purification and identification. The metabolic profile of the 14C residues recovered in the urine were determined using high pressure liquid chromatography (HPLC). The second step involved the determination of the metabolic profile of the 14C residues in excreta samples obtained from animals in the ADE study. Urine and fecal samples collected during the ADE study, which represented over 85 % of the excreted radioactivity, were composited by sex and group. The urine composites were analyzed directly by HPLC whereas the fecal composites were extracted with water and methanol and the extracts were analyzed. The peaks on the resulting chromatograms were matched with metabolites previously identified and quantitated.

The metabolic profile revealed that the 14C residues were distributed among four major and several minor metabolites.These degradates were compared to [Norbornene-2,3-14C] MGK 264 metabolites in rat urine identified previously by mass spectrometry in BTC Study No. P01933.The HPLC analysis indicated that the four major peaks had similar retention times to the MGK 264  metabolites identified in BTC Study No. P01933. The first metabolite (identified as Metabolite A) was formed by 13-oxidation of the side chain to produce a carboxylic acid and oxidation of the norbornene ring double bond to produce an epoxide. The second metabolite (identified as metabolite B) was an isomer of Metabolite A. The third metabolite (identified as Metabolite C) was formed by w-1 oxidation of the side chain to produce a carboxylic acid and oxidation of the norbornene ring double bond to produce an epoxide. The fourth metabolite (identified as metabolite D) was an isomer of Metabolite C. BTC study P01933 indicated that peak four contained a minor metabolite when co-eluted with Metabolite D. This minor metabolite was found to be the product of P-oxidation of the side chain to a carboxylic acid with the norbornene ring remaining intact and unchanged.The structure of MGK 264 and its major metabolites are shown in the final report attached to this end point.

The HPLC analysis of urine and feces from rats in the ADE phase of the study showed [Hexyl-l-14C]

MGK 264 was extensively metabolized prior to its elimination with only 1.83 % to 5.27% of the

administered dose excreted as unmetabolized MGK 264. The percent of administered dose excreted

as less polar metabolites (i.e., Metabolite C, Metabolite D, Zone 3 and Zone 4) in urine and feces was higher in females (44.72%-59.34%) than in males (30.93%-37.03%). Conversely, the percent of administered dose excreted as polar metabolites (i.e., Metabolite A, Metabolite B, Zone 1, Zone 2, Unknown 1) in urine and feces was higher in males (53.60%-62.41 %) than in females (34.79%-42.75%) indicating a sex difference in the quantitative metabolism of MGK 264.

Reference 3

Endpoint:

dermal absorption, other

Remarks:

Extent of dermal absorption and metabolic profile study in human volunteers

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline available

Principles of method if other than guideline:

The objective of the study was to determine the extent of dermal absorption and the route and rate of excretion and metabolic profile of MGK 264 in human volunteers after a single dermal application of 14C-MGK 264 to the forearm for eight (8) hours.

Clinical study involving 4 male volunteers that were dermally adminisitered 5 mg 14C labelled N-octylbicycloheptene dicarboximide (MGK 264) to a 4 cm x 6 cm area of the volar aspect of one forearm. Blood samples were collected from both forearms (ipsilateral or application arm and contralateral or non-application arm) at the same time intervals and the radioactivity in plasma was determined over time.
Eight hours after dose administration, the dose was removed by wiping the dosed area with isopropyl alcohol swabs and rinsing the area with isopropyl alcohol. The skin was stripped (tape stripping) with 3M tape 1, 23 and 45 hours after removal of the dosage. Urine and feces samples were collected when available for 5 consecutive days.

Urine samples were analysed by HPLC to investigate the metabolism of MGK 264 prior to elimination.

GLP compliance:

yes

Specific details on test material used for the study:

The test substance was [Hexyl-l- 14C] MGK 264. The radiolabeled test anicle was supplied by Amersham Corp. (Arlington Heights, IL; Code CFQ.6188). The structure and position of the label are shown in the frinal report attached to this end point record. The radiolabeled compound had a reported specific activity of 18.4 mCi/mmol and a reported radiochemical purity of 98%.

Radiolabelling:

yes

Species:

other: human

Sex:

male

Details on test animals or test system and environmental conditions:

Not allowed to bath/shower until last tape stripping on day 3. Kept at centre for 6 day after dosing.
Subjects not allowed medication/methylxanthine containing products/alcohol 48 hours before the start of the study.

Type of coverage:

semiocclusive

Vehicle:

other: isopropanol

Duration of exposure:

8 hours

Doses:

0.055 mg/kg bw (nominal)
5.0 mg MGK 264 in 100 microL: dosing solution

No. of animals per group:

4 males in study

Control animals:

no

Details on study design:

The application area on the volar aspect of the right or left forearm was outlined by an adhesive template (Duoderm®, Convatec/Squibb. J. C. Van Markenlaan, Rijswijk, The Netherlands) from which a rectangle of 4 cm x 6 cm had been removed. The dose was administered at about 9:00 a.m. on day 1 using a 100 μL glass WiretroI• micropipette (Drummond Scientific Corp., Broomall, PA). The dosage was spread over the entire application area using the glass micropipette, which was saved for residual analysis of radioactivity. The application area was then covered by an aluminum dome in which holes were made to provide for a nonocclusive condition. The dosage was left in place for eight (8) hours, during which the volunteers were free to move around under close supervision.

Signs and symptoms of toxicity:

not specified

Dermal irritation:

not specified

Total recovery:

The total mean recovery of radioactivity administered was 91.71 %

Key result

Time point:

8 h

Dose:

0.055 mg/kg bw

Parameter:

percentage

Absorption:

1.67 %

Remarks on result:

other: Based on a combination of radiolabelled material present in the urine and unaccounted for radioactivity (about 9%), a conservative dermal absorption value of 10% may be used for risk assessment purposes.

Radioactivity in Tape Strippings: the amount of radioactivity was the highest in the early strips and quickly decreased in the later strips, for each of the three days sampled. These data clearly showed that the radioactivity was present on the outer layers of the skin and did not accumulate in the skin.

Urine and faeces: The volunteers excreted a mean of 1.67% of the dosed radioactivity in the urine. The majority of the urinary radioactivity was present in the first 24 hour sample. The volunteers excreted none of the dosed radioactivity in the feces.

External recovery: The results clearly show that 88.72% of the dosed radioactivity remained on the surface of the skin 8 hours after dose administration.

Total recovery: The total recovery of radioactivity included radioactivity recovered from the urine, the feces, the external recovery (dome, swab and skin ri_nse), the glass micropipet, the tape strips and the gauze. The mean of the total recovery for the study was 91.71 %.

Distribution of 14C-Radioactivity in Urine: The distribution of metabolites in volunteer urine composites was summarized as a percent of radioactivity and the chromatograms showed the 14C radioactivity distributed between 2 predominant and several minor metabolites.

The distribution of urinary metabolites representing the percentage of total dose was calculated. Unmetabolized MGK 264 was only detected in Volunteer 02 BO urine where it accounted for 1.04% of the radioactivity in the urine and 0.02 % of the administered dose.

A comparison of the rat metabolic profile to human profile showed that four human metabolites had similar retention times to previously identified rat metabolites. The two predominant human metabolites had similar retention times to rat metabolites C and D. Metabolites C and D are isomers formed by 11-oxidation of the side chain to a carboxylic acid and oxidation of the norbornene double bond producing a stable epoxide. Together Metabolites C and D represented 54.51 % to 68.08% of the radioactivity in volunteer urine or 0.69% to 1.273% of the administered

dose. Human metabolites with the same retention times as rat metabolites A and B were also observed. Metabolites A and B are also isomers formed by P-oxidation of the side chain to a carboxylic acid and oxidation of the norbornene ring double bond producing a stable epoxide. Metabolites A and B combined represent 7.92% to 23.86% of the radioactivity in the urine and 0.09% to 0.55% of the administered dose.

Conclusions:

The total mean recovery of radioactivity administered was 91.71 %. A mean of 1.67% of the administered radioactivity was excreted in the urine and no measurable amount was excreted in the feces. The results obtained from tape stripping the skin clearly showed that the radioactivity did not accumulate in the skin.
It is therefore concluded that based on a combination of radiolabelled material present in the urine (about 1%) and unaccounted for radioactivity (about 9%), a conservative dermal absorption value of 10% may be used for risk assessment purposes.

Executive summary:

Four healthy male volunteers were dermally administered 5 mg 14C labelled N-octylbicycloheptene dicarboximide (MGK 264) to a 4 cm x 6 cm area of the volar aspect of the forearm. The radioactive dose applied was approximately 50 μCi. The application area was covered by a protective dome under nonocclusive conditions. Blood samples were collected from both forearms (ipsilateral and contralateral) at the same time intervals and the radioactivity in plasma was determined over time.

Eight hours after dose administration, the dose was removed by wiping the dosed area with isopropyl alcohol swabs and rinsing the area with isopropyl alcohol. The skin was stripped (tape stripping) with 3M tape 1, 23 and 45 hours after removal of the dosage. Urine and feces samples were collected when available for 5 consecutive days.

The total mean recovery of radioactivity administered was 91.71 %. A mean of 1.67% of the administered radioactivity was excreted in the urine and no measurable amount was excreted in the feces. The mean external recovery of radioactivity (dome, gauze, skin rinse and swabs) was 88. 72 % of the administered radioactivity. The results obtained from tape stripping the skin clearly showed that the radioactivity did not accumulate in the skin.

It is therefore concluded that based on a combination of radiolabelled material present in the urine (about 1%) and unaccounted for radioactivity (about 9%), a conservative dermal absorption value of 10% may be used for risk assessment purposes.

Reference 4

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

absorption

distribution

excretion

Qualifier:

no guideline available

Principles of method if other than guideline:

This study consisted of two experiments conducted in rats. In the first experiment, the radioactivity
in blood was determined at different time intervals following a single dermal administration of
[hexyl-l-14C] MGK 264. The second experiment involved the determination of the pharmacokinetics
and distribution patterns of [hexyl-l-14CJ MGK 264 following a single dermal application.
The rats were fasted for approximately 18 hours prior to the administration of the [hexyl-l-14c) MGK
264. Each male rat was administered 13.1 - 16.1 μCi of radioactivity.
In the first experiment, five male rats were administered a mean single dermal dose of [hexyl-l-14C]
MGK 264 at approximately 14 mg/kg body weight and the blood levels of radioactivity were
determined for a 120 hour period.The results of the blood kinetic experiment was then used for the second experiment.
In the second experiment, four groups of five rats were administered a single dermal dose of [hexyll-
14C] MGK 264 at approximately 13 mg/kg body weight. Based on the blood kinetic data, one
group was euthanized at each of the following time intervals; peak blood level (hour 12); blood halflife
(hour 43); second blood half-life (hour 74); and 168-hours post-dose administration. Urine and
feces were collected for all groups at predetermined intervals until the time of euthanasia. The rats
were euthanized and the treated skin and enclosures were removed and rinsed. The animals were
then necropsied and selected tissues and organs were harvested. Samples of urine, feces, tissues,
skin rinse and enclosure rinse were subsequently analyzed for radioactivity.

GLP compliance:

yes

Specific details on test material used for the study:

[hexyl-l-14C] MGK 264

Radiolabelling:

yes

Species:

rat

Strain:

other: CRL:CD Br

Details on species / strain selection:

The rat is a species commonly used for pharmacokinetic
studies and is the animal of choice for this study according to
the EPA Pesticide Assessment Guidelines. In addition, a number of
other toxicological evaluations have been and/or are scheduled to be
conducted on MGK 264 utilizing this strain of rat as the test animal

Sex:

male

Details on test animals or test system and environmental conditions:

All experiments were performed on adult male Charles River CD (CRL:CD Br) rats
obtained from Charles River Breeding Laboratories, Wilmington, Massachusetts.
The rats were approximately six weeks of age when received by the BTC. Upon
arrival, the test animals were transferred to a quarantine room where they were
eartagged and maintained in individual. hanging, stainless steel cages throughout the
two week quarantine period. Soon after their arrival, the animals were examined for
general health. The animals were weighed once each week during the quarantine
period and, with the exception of an eighteen hour period prior to dosing and a six
hour period post-dosing, received Purina Rodent Chow #5002 (Purina Mills, St.
Louis, MO) ad libitum. Water was provided ad libitum throughout the quarantine
and study periods.
Throughout the quarantine and study period the room temperature ranged between
69°F-72°F and the relative humidity ranged between 56%-64%. A 12 hour light,
12 hour dark cycle was established and the air exchange rate was at least seven per
hour.

Route of administration:

dermal

Vehicle:

other: isopropyl alcohol

Details on exposure:

The dose was delivered with a precalibrated 100 μL micropipette to an area on the
back within the glass enclosure (backpack). All doses were administered on a
constant volume basis i.e., 100 μL of dosing solution. The actual amount of
compound applied was measured by weight as a differential between the weight of
the micropipette before and after dosing. After the radiolabeled dosing, a
nonocclusive plastic cover was glued to cover the top of the backpack. Each
backpack was checked daily and reglued if necessary.

Duration and frequency of treatment / exposure:

all animals were dosed once (described above) and split into 4 exposure groups:
1 12 hours exposure before euthanasia
2 43 hours exposure before euthanasia
3 74 hours exposure before euthanasia
4 168 hours exposure before euthanasia

Dose / conc.:

14 mg/kg bw/day (nominal)

No. of animals per sex per dose / concentration:

4 groups of 5 male rats all recieved same dose

Positive control reference chemical:

not specified

Details on study design:

This study consisted of two experiments conducted in rats. The rats were fasted for approximately 18 hours before administration of MGK- 264. In the first experiment, the radioactivity
in blood was determined at different time intervals following a single dermal administration of
[hexyl-l-14C] MGK 264. The second experiment involved the determination of the pharmacokinetics
and distribution patterns of [hexyl-l-14CJ MGK 264 following a single dermal application.
The rats were fasted for approximately 18 hours prior to the administration of the [hexyl-l-14c) MGK
264. Each male rat was administered 13.1 - 16.1 μCi of radioactivity.
In the first experiment, five male rats were administered a mean single dermal dose of [hexyl-l-14C]
MGK 264 at approximately 14 mg/kg body weight and the blood levels of radioactivity were
determined for a 120 hour period.The results of the blood kinetic experiment showed that the blood
level of radioactivity was very low and the absorption of radioactivity was extremely slow following
a single dermal dose. Two peaks in blood radioactivity were reached, one at six hours and one at
twelve hours post-dose. The half-life was calculated to be 31.17 hours. Thisresult was then used for the second experiment:

In the second experiment, four groups of five rats were administered a single dermal dose of [hexyll-
14C] MGK 264 at approximately 13 mg/kg body weight. Based on the blood kinetic data, one
group was euthanized at each of the following time intervals; peak blood level (hour 12); blood halflife
(hour 43); second blood half-life (hour 74); and 168-hours post-dose administration. Urine and
feces were collected for all groups at predetermined intervals until the time of euthanasia. The rats
were euthanized and the treated skin and enclosures were removed and rinsed. The animals were
then necropsied and selected tissues and organs were harvested. Samples of urine, feces, tissues,
skin rinse and enclosure rinse were subsequently analyzed for radioactivity.

Details on dosing and sampling:

Urine and feces were collected for all groups at predetermined intervals until the time of euthanasia. The rats
were euthanized and the treated skin and enclosures were removed and rinsed. The animals were
then necropsied and selected tissues and organs were harvested. Samples of urine, feces, tissues,
skin rinse and enclosure rinse were subsequently analyzed for radioactivity.

Statistics:

The mean (x) and the standard deviation (SD) were used to characterize the data (i.e.,
radioactivity measurement, concentration, etc.). The half-life was calculated using
the Lotus 1-2-3 data regression program

Details on absorption:

MGK 264 was absorbed very slowly. The peak blood level of radioactivity was reached at approximately 12 hours and then decreased with time. At the 12 hour euthanasia interval, a maximum of 11.38% of the dosed radioactivity was absorbed. Significant amounts of the applied radioactivity remained on the skin, and were very slowly and continuously absorbed through the skin. The half-life of blood radioactivity was calculated to be 31 hours.

Details on distribution in tissues:

Group 1: The total radioactivity in tissue and carcass for each animal ranged between 5.07% and 9.38% of the dosed
radioactivity. A majority of the dosed radioactivity recovered in the tissues was present in the intestine with contents (5. 09 %).
Group 2: The total residue in tissue and carcass for each animal ranged between 4. 52 % and 7. 04 % of the dosed
radioactivity. A majority of the dosed radioactivity recovered in the tissues was present in the intestine with contents (4.32%).
Group 3: The total radioactivity in tissue and carcass for each animal ranged between 3.91 % and 15.49% of the dosed
radioactivity. A majority of the dosed radioactivity recovered in the tissues was present in the intestine with contents (5.68%).
Group 4: The total radioactivity in tissue and carcass for each animal ranged between 1.28% and 2.84%. A majority
of the dosed radioactivity recovered in the tissues was present in the intestine with contents (1.28%).
No accumulation of radioactivity in the body occurred.
Outside of the treated skin and carcass, the only tissues showing a significant percent of dosed radioactivity are the intestine with contents, fat and liver of which the intestine and liver are the main organs associated with the metabolism and excretion of the radioactivity via the feces. The levels of radioactivity seen in the fat decreased with time indicating that MGK 264 does not accumulate in the fat.

Details on excretion:

Group 1: The rats excreted a mean of 4.02% of the dosed radioactivity in their urine and 0.87% in their
feces. A mean of 4.90% of the dosed radioactivity was recovered in the urine and feces.
Group 2:The rats excreted a mean of 18.91 % of the dosed radioactivity in their urine and
9.50% in their feces. A mean of 28.40% of the dosed radioactivity was recovered in the urine and feces.
Group 3: The rats excreted a mean of 26. 73 % of the dosed radioactivity in their urine and 16.18% in their feces. A mean of 42.91 % of the dosed radioactivity was
recovered in the urine and feces.
Group 4: The rats excreted a mean of the 46.27% of the dosed radioactivity in their urine and 35. 92 % in their feces. The radioactivity recovered in the urine was excreted throughout the 168-hour collection time. A mean of 82.19% of the dosed radioactivity was recovered in the urine and feces.

Metabolites identified:

not measured

Conclusions:

The results of this study indicated that dermally applied MGK 264 was slowly absorbed from the skin with the absorbed radioactivity very quickly excreted via the urine and feces. These data also indicated that the enteroheptic circulation played a role in the elimination of MGK 264 from the body and that the radioactivity did not accumulate in any of the tissues studied.

Executive summary:

In the first experiment, five male rats were administered a mean single dermal dose of [hexyl-l-14C] MGK 264 at approximately 14 mg/kg body weight and the blood levels of radioactivity were determined for a 120 hour period. The results of the blood kinetic experiment showed that the blood level of radioactivity was very low and the absorption of radioactivity was extremely slow following a single dermal dose. Two peaks in blood radioactivity were reached, one at six hours and one at twelve hours post-dose. The half-life was calculated to be 31.17 hours. In the second xperiment, four groups of five rats were administered a single dermal dose of [hexyll-14C] MGK 264 at approximately 13 mg/kg body weight. Based on the blood kinetic data, one group was euthanized at each of the following time intervals; peak blood level (hour 12); blood halflife (hour 43); second blood half-life (hour 74); and 168-hours post-dose administration. Urine and feces were collected for all groups at predetermined intervals until the time of euthanasia. The rats were euthanized and the treated skin and enclosures were removed and rinsed. The animals were then necropsied and selected tissues and organs were harvested. Samples of urine, feces, tissues, skin rinse and enclosure rinse were subsequently analyzed for radioactivity.

For the animals euthanized at peak blood level of radioactivity, a majority of the administered radioactivity was recovered in the skin rinse (81.07%). For the animals euthanized at the blood half-life, second blood half-life or at 168-hours, the mean amounts of radioactivity in the skin rinse were 53.06%, 29.96% and 0.62%, respectively. As the time for euthanasia was lengthened, the compound was slowly absorbed from the skin and excreted in both the urine and feces. By 168 hours, the radioactivity recovered in the urine was 46.27% and in the feces was 35.92%.

The radioactivity recovered from the carcass was low at the 12, 43 and 74 hour euthanasia intervals and decreased at the 168-hour euthanasia interval, indicating that no accumulation of radioactivity in the body occurred. In general, mean tissue radioactivity decreased with time. The radioactivity did not accumulate in the tissues studied. Outside of the treated skin and carcass, the only tissues showing a significant amount of radioactivity were the intestines with content, fat and liver. The radioactivity present in the intestine with contents, liver and feces indicated that the enterohepatic circulation played a role in the elimination of MGK 264 from the body. The total mean percent of the administered dose recovered in the four groups ranged between 85. 35 % - 100. 65 % .

Reference 5

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1990-1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

according to guideline

Guideline:

EPA OPP 85-1 (Metabolism and Pharmacokinetics)

Principles of method if other than guideline:

This study was performed to support results from ADME in Rats study by determining if expired CO2 is a factor during metabolism of MGK 264 when administered orally.

GLP compliance:

yes

Specific details on test material used for the study:

[hexyl-l-14C] MGK 264

Radiolabelling:

yes

Species:

rat

Strain:

Sprague-Dawley

Details on species / strain selection:

Aquired from Charles River.

Sex:

male/female

Details on test animals or test system and environmental conditions:

The study was performed on four (2 males and 2 females) adult male and female Charles River CD rats (Charles Rivers Breeding Laboratories, Portage, Michigan) weighing between 115 and 141 g and approximately six weeks of age. Upon arrival, the test animals were transferred to a quarantine room where they were kept in individual cages throughout the quarantine period. Upon arrival, all animals received individual ear tags and were examined and found to be healthy. All the rats were quarantined for one week prior to dosing. The rats received Purina Rodent Chow and water ad libitum during the quarantine and study period. There are no known contaminants present in the diet or water which would affect the outcome of the study. Therefore, no analysis outside those provided by the manufacturer or the local water district was performed. During the quarantine and testing period, all animals were observed twice daily to ensure normal health. All animals were weighed and selected for test on October 23, 1990. As stated in the protocol, the animals were not randomized. The animal room temperature was kept at 71°F - 74°F and the humidity was maintained at 40% - 54% during the study period. The light cycle was 12 hours light, 12 hours dark .

Route of administration:

oral: gavage

Vehicle:

corn oil

Duration and frequency of treatment / exposure:

One dose applied by oral gavage

Dose / conc.:

100 mg/kg bw/day (nominal)

No. of animals per sex per dose / concentration:

2 males/ 2 females

Control animals:

no

Details on study design:

Immediately after dosing, the animals were transferred to their respective Roth glass metabolism cages. The cages were configured to enable the separate collection of urine, feces, and C02. Air drawn into the system was dried with Drierite and passed through Ascarite to render it carbon dioxide free. Expired CO2 was collected in a gas trap containing a 2:1 mixture of ethanolamine/cellusolve (-150 mL). The contents of the gas trap, urine and feces were collected at 2, 4, 8, 24 and 48 hours post dose. Aliquots (5 mL) of all trapping solutions were counted directly in Carbon 14 liquid scintillation cocktail. The urine and feces were discarded as radioactive waste.

Details on dosing and sampling:

The four rats (2 males, 2 females) used in this study were dosed with approximately 100 mg (Hexyl-1- 14C) MGK 264/kg body weight by oral gavage using a size 16 gauge intubation needle and a 3 cc syringe .

Statistics:

Radioactivity measurements were reported as zero, if values were equivalent or less than background. All values above background were reported as (Hexyl-1- 14C) MGK 264 equivalent. Background was subtracted from all samples counted. The formula used in the calculation of percent of dose is shown below:
Percent of dose in specific sample:
= Total DPM Recovered in Sample / Total DPM in Administered Dose x 100 The mean and standard deviation were used to characterize the data, where appropriate (i.e., radioactivity measurement, concentration, etc.) .

Type:

metabolism

Results:

The results from this study indicate that (Hexyl-1- 14C) MGK 264 is refractory to metabolic degradation to 14C02 in rats.

Details on absorption:

Not applicable

Details on distribution in tissues:

Not applicable

Details on excretion:

Not applicable

Details on metabolites:

Not applicable

14C0 2Trapped and Recovered in Ethanolamine/CellusolveExpressed as a Percent of Total Dose

 

 

Time	Female	Female	Female		Male	Male	Male
Interval	RatNo.	RatNo.	Mean	+/-Std.	RatNo.	RatNo.	Mean	+/-Std.
(Hours)	16252	16256	Values	Deviation	16217	16219	Values	Deviation
0-2	0.00	0.00	o.oo	0.00	0.00	0.00	0.00	0.00
2-4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
4-8	o.oo	0.00	0.00	0.00	0.01	0.01	0.01	0.00
8-24	0.01	0.01	0.01	0.00	0.01	0.01	0.01	0.00
24-48	0.01	0.00	0.01	0.01	0.00	0.00	0.00	0.00
Total	0.02	0.01	0.02	0.01	0.02	0.02	0.02	0.00

 

 

 

Conclusions:

Adult male and female Sprague-Dawley rats administered (Hexyl-1-14C) MGK 264 by oral gavage expired minimal amount of radioactivity as 14co2 during 48 hours. There is no difference in the expiration of CO2 between males and females. These result indicate that the 14C radiolabel is in a stable portion of the MGK 264 molecule and that (Hexyl-1-14C) MGK 264 is refractory to metabolic degradation to 14CO2 in rats when administered orally.

Executive summary:

Exhaled CO₂study - The objective of this study was to determine if rats dosed with (Hexyl-1- 14C) MGK 264 would exhale 14CO₂. The study was intended to produce data that fortifies a greater understanding of the general metabolism of (Hexyl-1- 14C) MGK 264. The study was conducted in accordance with EPA Pesticide Assessment Guidelines, Subdivision F, Series 85-1 and Good Laboratory Practice Standards (40 CFR, Part 160). Four Charles River CD rats (2 males, 2 females) were used to determine the amount of 14C02 expired following a single oral dose of (Hexyl-1-1 4C) MGK 264. The dose level of (Hexyl-1-14C) MGK 264 was 100 mg/kg body weight. The animals were administered a single dose by oral gavage. After dosing, all animals were immediately placed in Roth metabolism cages. Expired 14C02 was collected in a gas trap containing ethanolamine/cellusolve (2/1; V/V). Samples were collected at 2, 4, 8, 24 and 48 hours after dosing and the 14C radioactivity was determined. After forty-eight hours the 14C radioactivity recovered from the male or female rats averaged 0.02% of the total dose.

Description of key information

For MGK 264 there is a comprehensive package of absorption, metabolism, distribution and excretion information in rats and a dermal absorption study in human volunteers.

A pharmacokinetic and distribution study was performed in the rat after a single dermal application of radiolabelled MGK 264 (BTC Study No. P02072, Selim, S. 1992). In the first experiment, five male rats were administered a mean single dermal dose of [hexyl-l-14C] MGK 264 at approximately 14 mg/kg body weight and the blood levels of radioactivity were determined for a 120 -hour period. The results of the blood kinetic experiment showed that the blood level of radioactivity was very low and the absorption of radioactivity was extremely slow following a single dermal dose. Two peaks in blood radioactivity were reached, one at six hours and one at twelve hours post-dose. The half-life was calculated to be 31.17 hours. In the second experiment, four groups of five rats were administered a single dermal dose of [hexyll-14C] MGK 264 at approximately 13 mg/kg body weight. Based on the blood kinetic data, one group was euthanized at each of the following time intervals; peak blood level (hour 12); blood half-life (hour 43); second blood half-life (hour 74); and 168-hours post-dose administration. Urine and faeces were collected for all groups at predetermined intervals until the time of euthanasia. The rats were euthanized and the treated skin and enclosures were removed and rinsed. The animals were then necropsied and selected tissues and organs were harvested. Samples of urine, faeces, tissues, skin rinse and enclosure rinse were subsequently analysed for radioactivity. For the animals euthanized at peak blood level of radioactivity, a majority of the administered radioactivity was recovered in the skin rinse (81.07%). For the animals euthanized at the blood half-life, second blood half-life or at 168-hours, the mean amounts of radioactivity in the skin rinse were 53.06%, 29.96% and 0.62%, respectively. As the time for euthanasia was lengthened, the compound was slowly absorbed from the skin and excreted in both the urine and faeces. By 168 hours, the radioactivity recovered in the urine was 46.27% and in the faeces was 35.92%. The radioactivity recovered from the carcass was low at the 12, 43 and 74 hour euthanasia intervals and decreased at the 168-hour euthanasia interval, indicating that no accumulation of radioactivity in the body occurred. In general, mean tissue radioactivity decreased with time. The radioactivity did not accumulate in the tissues studied. Outside of the treated skin and carcass, the only tissues showing a significant amount of radioactivity were the intestines with content, fat and liver. The radioactivity present in the intestine with contents, liver and faeces indicated that the enterohepatic circulation played a role in the elimination of MGK 264 from the body. The total mean percent of the administered dose recovered in the four groups ranged between 85. 35 % - 100. 65 %. The results of this study indicated that dermally applied MGK 264 was slowly absorbed from the skin with the absorbed radioactivity very quickly excreted via the urine and faeces. These data also indicated that the enterohepatic circulation played a role in the elimination of MGK 264 from the body and that the radioactivity did not accumulate in any of the tissues studied.

 

A multiple dermal application rat study was performed to investigate the pharmacokinetics and distribution of MGK 264 (BTC Study No. PO2073, Selim, S. 1992). This study consisted of two experiments conducted in rats. The first experiment involved the determination of the blood concentration of radioactivity with time, the determination of peak blood level and half-life of radioactivity in blood, following multiple dermal administration of non-radiolabelled MGK 264 for fourteen consecutive days followed by a single dermal administration of [Hexyl-l-14C] MGK 264 on day 15. The second experiment involved the euthanasia of animals at peak blood level of radioactivity, first and second half-life of radioactivity and at 168 hours following the same dosing regimen. The purpose of the second study was to determine the tissue distribution, rate and route of excretion and balance of radioactivity at the time of euthanasia. Prior to the initiation of this study, an identical study was performed with the exception that a single dermal dose of 14C-MGK 264 was applied (BTC Study No. P02072). The comparison of the blood concentration of radioactivity with time and the tissue distribution and excretion between the single and multiple dermal doses are presented in this report. In the first experiment, five male rats were administered a daily dose of 100 μL of an isopropyl alcohol solution containing 5 % (w/w) of non-radiolabelled MGK 264 for fourteen consecutive days. On day 15, each rat was administered a single dermal dose of 100 μL of 5% w/w [Hexyl-l-14C] MGK 264 in isopropyl alcohol. Each rat received approximately 12 mg/kg body weight and between 13.9-14.5 μCi of radioactivity. The rats were fasted for approximately 18 hours prior to the first day of dosing with the non-radiolabelled solution and prior to the administration of the radiolabelled solution. Following the radiolabelled dose, blood samples were collected from the tail vein at different time intervals over a 120-hour period and the radioactivity in blood was determined. Blood radioactivity was very low at all time intervals (2 to 3 times background) suggesting that the absorption of radioactivity was extremely slow. Two radioactive peaks were present in blood, one at six hours post-dose administration and one at ten hours post-dose administration. The half-life of blood radioactivity was calculated to be 28.5 hours. Since these results were very close to the peak (12 hours) and half-life (31 hours) determined in the single dermal dose study, the decision was made to use the same time of euthanasia from the single dermal dose, so that data from the two regimens could be compared. In the second experiment, four groups of five male rats and one group of five female rats were administered multiple dermal doses of MGK 264 as described for the blood kinetics study followed by a single dermal dose of [Hexyl-l-14C] MGK 264 at approximately 12 mg/kg body weight for the males and 17 mg/kg body weight for the females. Each rat was administered between 13. 9-14. 2 μCi of radioactivity. Based on the blood kinetic data, one group of five males was euthanized at each of the following time intervals; peak blood level of radioactivity (12 hours); blood half-life (43 hours) and second blood half-life of radioactivity (74 hours); and 168-hours post-dose administration. The group of five females was euthanized at 168-hours post-dose. Urine and faeces were collected for all groups at predetermined time intervals until the time of euthanasia. When the rats were euthanized, the treated skin and enclosures were removed and rinsed, the animals were then necropsied and selected tissues and organs were harvested. Samples of urine, faeces, tissues, skin rinse and enclosure rinse were subsequently analysed for radioactivity.

For the animals euthanized at peak blood level of radioactivity, a majority of the administered radioactivity (71. 85 %) was recovered in the skin rinse. For the animals euthanized at blood half-life and second blood half-life of radioactivity, the mean percentages of dosed radioactivity in the skin rinse were 49. 54 % and 3 7 .54 % respectively. For the males and females euthanized at 168-hours, the mean percentages of dosed radioactivity in the skin rinse were 8.09% and 0.44%, respectively. The dosed radioactivity was slowly absorbed from the skin. By 168 hours, a majority of the administered radioactivity was excreted through the urine (51.48% for the males, 69.29% for the females) with a significant amount of radioactivity recovered from the faeces (30.37% for the males, 27.65% for the females). This indicated that biliary excretion played an important role in the elimination of radioactivity from the body.

The radioactivity recovered from the carcass decreased with time indicating that no accumulation of radioactivity in the body occurred. In general, mean tissue radioactivity decreased with time and did not accumulate in the tissues studied. The total mean percent of administered dose recovered in the four groups ranged between 99.40% - 104.96%. A comparison of the results of the single dose and multiple dose studies indicated that, with the exception of a higher amount of radioactivity present in the skin at the different euthanasia time intervals, following the multiple dose administration, the patterns of absorption, tissue distribution and elimination between the single and multiple doses are comparable.

 

Absorption, distribution, metabolism and extraction studies (ADME) studies -Four experiments were conducted as part of this study (BTC Study No. PO1932, Selim, S. 1992 and BTC Study No PO1932 Addendum, Selim, S. 1993). The experiments involved the determination of the absorption, distribution, metabolism and excretion (ADME) patterns following the administration of [Hexyl-l-14C] MGK 264 at a single oral low dose, a single oral high dose, and a multiple oral low dose. In addition, rat blood kinetics were determined following a single oral low dose administration. Ten rats(5males and5females) were used in each of the four experiments. The rats were fasted for approximately 18 hours prior to the administration of the [Hexyl-l-14C] MGK 264. Each animal was administered approximately 18-30μCiof radioactivity. With the exception of the single high oral dose, 100 mg/kg of [Hexyl-l-14C] MGK 264 was administered. In the single high oral dose, 1000 mg/kg [Hexyl-l-14C] MGK 264 was administered. Rats in the multiple oral low dose experiment were given a daily oral low dose of 100 mg/kg of the non-labelled compound by gavage for two weeks followed by a single oral low dose of the labelled compound. Urine and faeces were collected for all groups at predetermined intervals. Seven days after dose administration, the rats were euthanised and selected tissues and organs were harvested. Samples of urine, faeces and tissues were subsequently analysed for 14C content.

In the blood kinetics study, radioactivity peaked at approximately 4 hours for males and 6 hours for females. In all of the definitive experiments, 49.49% - 73.05% of the recovered radioactivity was found in the urine and 20.87% - 46.67% in the faeces. Tissue residues of 14C were less than 0.43% of the administered dose in all groups. The total mean recovered radioactivity of the administered dose in the three groups ranged between 93.13% - 97.43%.

Metabolism and identification of metabolites was investigated by the quantitation of the 14C residues in the excreta of rats orally administered [Hexyl-l-14C] MGK 264. Three oral dosage regimens were evaluated. These included: a single oral low-dose (I 00 mg/kg), a single oral high-dose (1,000 mg/kg) and a multiple oral low-dose (animal preconditioned with 100 mg/kg of non-radiolabelled MGK 264 for 14 days followed by a 100 mg/kg dose of [Hexyl-l-14C] MGK 264 on day 15). The metabolism phase of this study was undertaken in two steps. First, additional male and female rats were orally dosed with [Hexyl-V4C] MGK 264 at 859 mg/kg and 697 mg/kg, respectively. Urine and faeces were collected from these animals in order to obtain a sufficient mass of 14C residues for metabolite isolation, purification and identification. The metabolic profile of the 14C residues recovered in the urine were determined using high pressure liquid chromatography (HPLC). The second step involved the determination of the metabolic profile of the 14C residues in excreta samples obtained from animals in the ADE study. Urine and faecal samples collected during the ADE study, which represented over 85 % of the excreted radioactivity, were composited by sex and group. The urine composites were analysed directly by HPLC whereas the faecal composites were extracted with water and methanol and the extracts were analysed. The peaks on the resulting chromatograms were matched with metabolites previously identified and quantitated.

The metabolic profile revealed that the 14C residues were distributed among four major and several minor metabolites. The HPLC analysis indicated that the four major peaks had similar retention times to the MGK 264  metabolites identified in BTC Study No. P01933. The first metabolite (identified as Metabolite A) was formed by 13-oxidation of the side chain to produce a carboxylic acid and oxidation of the norbornene ring double bond to produce an epoxide. The second metabolite (identified as metabolite B) was an isomer of Metabolite A. The third metabolite (identified as Metabolite C) was formed by ω-1 oxidation of the side chain to produce a carboxylic acid and oxidation of the norbornene ring double bond to produce an epoxide. The fourth metabolite (identified as metabolite D) was an isomer of Metabolite C. BTC study P01933 indicated that peak four contained a minor metabolite when co-eluted with Metabolite D. This minor metabolite was found to be the product of P-oxidation of the side chain to a carboxylic acid with the norbornene ring remaining intact and unchanged.

The HPLC analysis of urine and faeces from rats in the ADE phase of the study showed [Hexyl-l-14C] MGK 264 was extensively metabolized prior to its elimination with only 1.83 % to 5.27% of the administered dose excreted as unmetabolized MGK 264. The percent of administered dose excreted

as less polar metabolites (i.e., Metabolite C, Metabolite D, Zone 3 and Zone 4) in urine and faeces was higher in females (44.72%-59.34%) than in males (30.93%-37.03%). Conversely, the percent of administered dose excreted as polar metabolites (i.e., Metabolite A, Metabolite B, Zone 1, Zone 2, Unknown 1) in urine and faeces was higher in males (53.60%-62.41 %) than in females (34.79%-42.75%) indicating a sex difference in the quantitative metabolism of MGK 264.

In addition to HPLC analysis on collected excreta, following preliminary extraction and clean-up procedures, the 14C residues in urine were isolated and purified using high pressure liquid chromatography (HPLC) and identified by thermospray liquid chromatography mass spectrometry (LC/MS) and particle beam mass spectrometry (LC/EIMS) and gas chromatography/ mass spectrometry (GC/MS). Four major peaks were isolated from urine by HPLC and characterized by mass spectrometry. The first metabolite (identified as Metabolite A) was formed by β-oxidation of the side chain to produce a carboxylic acid and oxidation of the norbornene ring double bond to produce an epoxide. The second metabolite (identified as Metabolite B) had the same fragmentation pattern as Metabolite A and is an isomer of Metabolite A. The third metabolite (identified as Metabolite C) was formed by ω-loxidation of the side chain to produce a carboxylic acid and oxidation of the norbornene ring double bond to produce an epoxide. The fourth metabolite (identified as Metabolite D) showed a similar fragmentation pattern to Metabolite C and is an isomer of Metabolite C. TheGC/MSindicated that peak four also contained a minor metabolite which coeluted with Metabolite D. The mass spectra indicated it was the product of beta-oxidation of the side chain with the norbornene ring remaining intact and unchanged. The HPLC analysis of urine and faeces from rats in the ADE phase of the study showed [Norbornene-2,3-14C] MGK 264 was extensively metabolized prior to its elimination. MGK 264 was not detected in the urine and only 0.07%-2.57% of the administered dose was excreted in the faeces as unmetabolized MGK 264. The percent of administered dose excreted as less polar metabolites (Metabolite C, Metabolite D and Zone 4) in the urine was higher in the females (45.96%-52.43%) than in the males (19.98%-33.92%). Further, the percent of administered dose excreted as polar metabolites (i.e., Metabolite A, Metabolite B, Zone 1, Unknown 1) in faeces was higher in males (26.35%-3l.05%) than in females (12.57%-14.48%) indicating a sex difference in the quantitative metabolism of MGK264.

ADME conclusion - following administration, [Hexyl-l-14C] MGK 264 is very quickly absorbed (oral doses) with peak plasma levels detected at 4 hours in males and 6 hours in females. The half-life of radioactivity in the blood was found to be 8 hours in males and 6 hours in females. The total percentage absorption following an oral administration of MGK 264 was not reported. MGK 264 is extensively metabolized prior to its elimination with only 1.83 % to 5.27% of the administered dose excreted as unmetabolized MGK 264. Excretion is rapid and is predominantly in the urine and faeces, with very little tissue accumulation. The HPLC analysis of urine and faeces from rats in the ADE phase of the study showed the percent of administered dose excreted as less polar metabolites in urine and faeces was higher in females (44.72%-59.34%) than in males (30.93%-37.03%). Conversely, the percent of administered dose excreted as polar metabolites in urine and faeces was higher in males (53.60%-62.41 %) than in females (34.79%-42.75%) indicating a sex difference in the quantitative metabolism of MGK 264.

 

Exhaled CO₂study - The objective of this study was to determine if rats dosed with (Hexyl-1- 14C) MGK 264 would exhale 14CO₂. The study was intended to produce data that fortifies a greater understanding of the general metabolism of (Hexyl-1- 14C) MGK 264. The study was conducted in accordance with EPA Pesticide Assessment Guidelines, Subdivision F, Series 85-1 and Good Laboratory Practice Standards (40 CFR, Part 160). Four Charles River CD rats (2 males, 2 females) were used to determine the amount of 14C02 expired following a single oral dose of (Hexyl-1-1 4C) MGK 264. The dose level of (Hexyl-1-14C) MGK 264 was 100 mg/kg body weight. The animals were administered a single dose by oral gavage. After dosing, all animals were immediately placed in Roth metabolism cages. Expired 14C02 was collected in a gas trap containing ethanolamine/cellusolve (2/1; V/V). Samples were collected at 2, 4, 8, 24 and 48 hours after dosing and the 14C radioactivity was determined. After forty-eight hours the 14C radioactivity recovered from the male or female rats averaged 0.02% of the total dose.

The results from this study indicate that (Hexyl-1- 14C) MGK 264 is refractory to metabolic degradation to 14C02 in rats.

 

Dermal absorption study

The assessment of absorption and mass balance in healthy volunteers was investigated after topical application of 14C labelled MGK 264. Following application of MGK 264 the radioactivity in plasma was determined over time and urine and faeces samples were collected for 5 consecutive days. Urine samples were analysed by HPLC to determine the metabolic profile of MGK 264 in human volunteers and compare it to the identified rat metabolites.

The total mean recovery of radioactivity administered was 91.71 %. A mean of 1.67% of the administered radioactivity was excreted in the urine and no measurable amount was excreted in the faeces. The mean external recovery of radioactivity (dome, gauze, skin rinse and swabs) was 88. 72 % of the administered radioactivity. The results obtained from tape stripping the skin clearly showed that the radioactivity did not accumulate in the skin.

HPLC analyses of composite urine from the volunteers showed MGK 264 was extensively metabolized prior to its elimination. A small amount of MGK 264 was detected in the urine of volunteer 02 BO, where it accounted for 1.04% of the radioactivity in the urine and 0.02 % of the administered dose. The 14C urinary radioactivity was distributed among 2 predominant peaks and several minor peaks. These degradates were compared, by HPLC, to four (4) metabolites of MGK 264 identified previously by mass spectrometry in rat urine (BTC Study No. P01933). The analysis showed that the two predominant and two of the minor metabolites had similar retention times to the four rat metabolites characterized.

The two predominant human metabolites had similar retention times to rat metabolites C and D. Metabolites C and D are isomers formed by ,6-oxidation of the side chain to produce a carboxylic acid and oxidation of the norbornene double bond creating a stable epoxide. Together, C and D represented 54.51 % to 68.08% of the radioactivity in the urine or 0.69% to 1.27% of the administered dose. In addition, two human metabolites, had the same retention times as rat metabolites A and B. Metabolites A and B are isomers formed byβ-oxidation of the side chain to carboxylic acid and oxidation of the norbornene ring double bond resulting in a stable epoxide. Metabolites A and B combined, represented 7.92% to 23.86% of the radioactivity in the urine or 0.09 % to 0.55 % of the administered dose.

The total mean recovery of radioactivity administered was 91.71 %. A mean of 1.67% of the administered radioactivity was excreted in the urine and no measurable amount was excreted in the faeces. The results obtained from tape stripping the skin clearly showed that the radioactivity did not accumulate in the skin.

It is therefore concluded that based on a combination of radiolabelled material present in the urine (about 1%) and unaccounted for radioactivity (about 9%), a conservative dermal absorption value of 10% may be used for risk assessment purposes.

 

 

 

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

10

Absorption rate - inhalation (%):

100

Additional information

In the absence of experimental data for percentage absorption of MGK 264 by the oral and inhalation routes, default values of 100% will be used in risk assessments.