Registration Dossier

Administrative data

Endpoint:
basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to the EPA OPP 85-1 Guideline in compliance with GLP.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1995
Report Date:
2000

Materials and methods

Objective of study:
toxicokinetics
Test guideline
Qualifier:
according to
Guideline:
EPA OPP 85-1 (Metabolism and Pharmacokinetics)
Deviations:
yes
Remarks:
The weights of the male animals at the time of dosing were outside the range however, were within the target age range of 7-14 weeks.
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Test material form:
other: White solid
Details on test material:
- Name of test material (as cited in study report): MON 13900
- Physical state: White solid
- Laboratory sample codes: T-920008 (Group P3), T-920009 (Group P2), T-920019 (Groups P1, P4), T-920120 (Group P5), T-920190 (Groups D, H), T-930031 (Group B), T-930045 (Group C, FB repeats), T-930067 (Group A), T-930037 (Group C pre-dosing)
- Radiochemical purity (if radiolabelling): >99%
- Specific activity (if radiolabelling): 46.3 (Groups P1-P4), 2.02 (Group P5), 24.2 (Group A), 25.2 (Groups B, C), 2.63 (Groups D, H) mCi/mMol
- Locations of the label (if radiolabelling): Methylene carbon atom adjacent to the nitrogen atom of the oxazolidine ring
Radiolabelling:
yes

Test animals

Species:
rat
Strain:
other: Sprague-Dawley (CD)
Sex:
male/female
Details on test animals and environmental conditions:
-Source: Charles River Breeding Laboratory, Portage, MI
-Quarantine period: 10 d
-Method of assignment: Computer-generated scheme, by weight
-Method of identification: Individual ear-tag, barcoded cage card
-Age on Day of Dosing: 51-65 d (males), 56-71 d (females)
-Weight on day of dosing: 236-36 1 g (males); 170-242 g (females)
-Type of housing: Individual stainless steel cages with wire mesh bottoms, or Roth-type metabolism cages
-Water Availability: Ad libitum (St. Louis public water supply which is treated with sodium zeolite upon entering the building)
-Food Availability: Ad libitum (Purina Mills Certified Rodent Chow #5002)

All rats were quarantined for at least 10 d before being placed on study. The animal's diet consisted of certified purina rat chow® pellets and water ad libitum. Rats of group P5 were acclimated to Purina Rat Chow® meal and water bottles 4 d prior to dosing. A 12 h light/dark cycle was provided in an environment controlled room. Animals of group P1 were individually housed in roth-type metabolism cages for collection of expired gases after receiving an oral dose. Animals of group P5 were individually housed in modified stainless metabolism cages to accommodate a spring tether through which bile flowed. All other groups of animals were housed separately in stainless steel metabolism cages. Following dosing, all rats were supplied with certified purina rat chow® pellets and water ad libitum, except rats of group P5 were offered Certified Purina Rat Chow® meal from petri dishes and a 5% glucose/saline solution ad libitum from water bottles subsequent to dosing to maintain electrolyte balance.

Administration / exposure

Route of administration:
other: By oral gavage or intravenous injection
Vehicle:
other: Emulphor (for oral doses) and emulphor:ethanol:saline (1:1:8) ( for intravenous doses)
Details on exposure:
The test substance for animals receiving the oral dose was dissolved in Emulphor. All dosing solutions were aliquoted by weight, diluted and weighed portions were counted by Liquid Scintillation Counting (LSC) to determine concentration. The test substance for the intravenous dose was received in Emulphor. A stir bar was added to the flask, and alcohol was added and stirred to obtain a solution. Finally, saline was slowly added and stirred to give a ratio of emulphor:alcohol:saline of 1:1:8. This solution was also aliquoted by weight, diluted and weighed portions were counted by LSC. Rats of group P5 (biliary excretion group) were anesthetized with an acepromazine/ketamine mixture administered by intraperitoneal injection. The bile ducts were cannulated with PE 10 tubing, and the cannulae were exteriorized above the scapulae. The muscle was closed with continuous sutures while the skin was closed with interrupted sutures. The animals were fitted with rodent jackets which were equipped with stainless steel flexible springs through which the cannulae passed. The springs also protected the catheters. The end of the spring was attached to the jacket with Velcro. At the opposite end of the flexible spring was a cylindrical swivel. The PE 10 tubing was inserted into PE 50 tubing and strengthened with a drop of acrylic adhesive. The PE 50 was attached to the bottom of the swivel in an off-set configuration. An additional piece of PE 50 tubing, measuring approx 17 inches, was placed on top of the swivel. The rats were allowed to recover from the anesthesia before dosing. When the animals had recovered, they were dosed by gavage with 14C test substance and were placed in modified metabolism cages. The spring and the swivel passed through an opening at the top of the cage which was held in position by clamps attached to brackets above the cage. The collection vials were placed at animal height to allow for continuous bile flow.

Rats administered the test substance orally were dosed by gavage using a 1 or 2 mL glass syringe fitted with a straight Perfektem 16 or 18 gauge 2-inch animal feeding needle. Animals administered the test substance intravenously were dosed using a 1-mL glass syringe fitted with a 5/8 inch needle. Actual doses administered to each rat were calculated by weighing the syringes plus needle before and after dosing. For animals receiving the intravenous dose, a moistened piece of tissue was used to blot the injection site. These tissues were placed in scintillation vials and 15 mL Ultima gold counting cocktail was added and the dpm quantitated from the injection site was subtracted from the dose each animal received. The target dose volume was 4 mL/kg bw. In a few cases in which an animal was inadvertantly mis-dosed, an extra study animal was assigned the animal number of the mis-dosed animal and was dosed immediately. No data were collected from the mid-dosed animals.
Duration and frequency of treatment / exposure:
Definitive group includes single low intravenous dose (group A - at a target dose level of 1.25 mg/kg bw), a single low oral dose (group B - at a target dose level of 1.25 mg/kg bw), a repeated oral dose (group C -at a target dose level of 1.25 mg/kg bw; 14 consecutive doses of unlabelled substance followed on Day 15 by a single oral dose of labelled test substance) and a single high oral dose (group D - at a target dose level of 125 mg/kg bw).
Doses / concentrations
Remarks:
Doses / Concentrations:
The oral doses were administered at 1.25 or 125 mg/kg in emulphor and the intravenous doses were administered at 1.25 mg/kg in emulphor:ethanol:saline (1:1:8 v/v).
No. of animals per sex per dose:
2-3/sex for the preliminary study and 5/sex for definitive study
Control animals:
no
Details on study design:
The study consisted of six preliminary experiments (groups P1-P5 and H) designed to determine CO2 expiration, blood plasma concentration after oral and intravenous administration, tissue distribution by whole body autoradiography and biliary excretion, and a definitive study consisting of four groups (single intravenous low dose, single oral low dose, repeat oral low dose and single oral high dose). A summary of the treatment groups is given in Table 1.
Details on dosing and sampling:
Sample collection: Urine and faeces were collected from animals of groups P1, P5 and A - D at 6, 12 and 24 h after dosing and daily thereafter until animals were sacrificed. Cage washes were conducted at each collection period except for Group P5 for which a single cage wash was conducted at the 48 h sacrifice. Bile samples were collected from group P5 every 6 h for 48 h. Blood samples were collected from groups P2 and P3 at 0.25, 0.50, 1, 3, 6, 9, 12 and 24 h after dosing and then daily thereafter until animals were sacrificed after 5 d. Tissues from groups A - D were collected following sacrifice at 7 d. All tissues and excreta, except cage wash samples were stored in glass containers immediately after collection. Carcasses were stored in plastic bags before processing and in aluminum foil after they were processed through a meat grinder.

Sample storage: All samples were stored frozen at -200⁰C.

Radioactivity measurement: Radioactivity was measured by combustion and/or liquid scintillation counting.

Sample preparation:
-General Processing: Urine, plasma and cage wash samples were analyzed for radioactivity by counting aliquots (~0.1-0.5 g) by liquid scintillation counting (LSC). Aliquots (0.1- 0.3 g) of all other tissues and the fecal samples were combusted in a sample oxidizer using a burn cycle which was monitored by a sensor and was appropriate for each sample burned. The scintillation cocktail was a mixture 14C calibration standard and an oxidizer memory were run after approx each forty experimental samples to monitor oxidizer performance. Tissue samples and excreta were analyzed in duplicate. Five aliquots of each carcass were assayed and averaged. Assays not within ± 10% of the mean of the replicates were reassayed except when the sample was depleted, when dpm were less than twice the background, or when the percent of dose was considered insignificant (<0.01%). For this study, background counts ranged from approx 35-75 dpm, depending on sample type. Specific details of sample processing for the tissues and excreta in this study are described below:
-Urine, feces and cage washes: The fecal collections were homogenized with water and weighed. Duplicate aliquots (0.1-0.3 g) of the fecal homogenates were combusted. Duplicate aliquots of the urine (0.1-0.2 g) and cage wash samples (0.8-1.0 g) were weighed and analyzed directly by LSC. The urine, feces and cage washes were analyzed separately for each rat at each collection period.
-Bile samples: Weighed aliquots of bile samples (0.05-0.1 g) were analyzed in duplicate by LSC.
-Blood samples: In-life blood samples, taken from the tail, were collected in duplicate in heparinized capillary tubes. Immediately after collection, the capillary tubes were centrifuged for 5 min at 2500 rpm. The capillary tubes were broken at the interface between the plasma and the cellular fraction. The plasma contents were expressed into scintillation vials and counted directly by LSC. The cellular fraction was weighed onto combustopads, combusted and counted. Portions of the whole blood taken at sacrifice were separated into plasma and cells. The tubes containing the blood were centrifuged for approx 10 min at 3000 rpm. Duplicate portions of the whole blood and cellular fraction were combusted and analyzed for radioactivity by LSC. The plasma samples were counted directly by LSC.
-Tissues: Each adrenal, eye, ovary and thyroid were weighed individually and combusted. All other tissues were minced, and duplicate aliquots (0.1-0.3 g) of the minced tissues were combusted.
-Carcass: Individual carcasses were ground in a meat grinder, and five aliquots were combusted. Tails from animals receiving the dose intravenously were individually analyzed to ensure good dosing technique. A larger localized recovery (>0.5%) any section of the tail would have indicated that the dose had not been injected quantitatively into the tail vein.
-Whole body autoradiography: One male and one female rat at both the single oral low dose (group P4, 1.25 mg/kg bw) and the single oral high dose (group H, 125 mg/kg bw) were sacrificed at two time points (24 h and 5 d after dosing for group P4, 24 h and 7 d for group H) by CO2 inhalation. The animals were frozen in a hexane/dry ice bath, coated with a carboxymnethylcellulose solution and then completely embedded in a carboxymethylcellulose solution which was contained in a regular microtome stage. The entire stage was frozen in a hexane/dry ice bath. Sagittal sections were taken throughout the animal and affixed to tape. The sections were allowed to dry, labeled and pressed onto x-ray film.
Statistics:
The weights and the liquid scintillation counter data were processed by written by the data processing group at the Environmental Health Laboratory. The data were assembled, stored and processed with these programs. Additional data processing was conducted using Microsoft Excel software. The data are presented as the mean ± the standard error of the mean (SEM) for the number of animals indicated and the Student's t-test was used to detect statistical differences between sexes, dosing regimes or dose levels.

Results and discussion

Main ADME resultsopen allclose all
Type:
absorption
Results:
70% -83% at the low oral dose and repeated low oral dose and approx 54% -66% at the high dose
Type:
excretion
Results:
58 to 77% of the test substance via feces and 11 to 24% via urine
Type:
distribution
Results:
The total radioactivity associated with the tissues and carcass accounted for less than 1.7% of the administered dose.

Toxicokinetic / pharmacokinetic studies

Details on absorption:
The following conclusions about absorption of the test substance were made based on comparison of the amounts of radioactivity excreted in the urine at the low dose level (1.25 mg/kg bw) following oral administration with that obtained after intravenous dosing. The single oral low dose was well absorbed (70.0% and 83.1% for males and females, respectively); absorption of the single oral low dose was not affected by pretreatment with repeated doses (68.5% and 85.0% for males and females, respectively). Absorption by female rats was greater than for the males, regardless of route of administration or dose level. Absorption at the high dose (53.7% and 66.1% for males and females, respectively) was somewhat lower than at the low dose.
Details on distribution in tissues:
The data show that very little test substance derived radioactivity remained in any tissue 7 d after dosing. The amount remaining in the tissues, collectively, including the blood and gut contents ranged from 0.52-1.12% for groups A-D. The residual carcass was analyzed separately and contained 0.08-0.56% of the dose after 7 d. Thus, the total amount of the dose remaining in the animal (tissues, blood, gut contents and carcass) after 7 d ranged from 0.77 to 1.65%. Minor statistical differences were noted between males and females or between groups in the radioactivity remaining in the carcass, gut contents, blood and tissues. Females generally had slightly higher levels of radioactivity remaining in the tissues than did males. Analysis of tissue distribution at 7 d after dosing demonstrated generally low levels of radioactivity in most tissues with no tissue accounting for more than 1% of the dose. The only tissue that showed any evidence of significant amounts of radioactivity following oral administration was the liver which accounted for up to 0.88% of the dose. The percent of dose remaining in the liver was significantly greater for females than males at the low, repeated low and high dose groups, but not the intravenous dose. The percent of dose remaining in the liver was greater for both males and females that received the low oral dose compared to those that received the oral high dose. Other than the liver, the only other tissues which exceeded 0.1% of the dose in any group were kidney (0.06-0.11% for the intravenous dose, 0.02-0.03% for the oral doses), muscle (0.09-0.18% of the dose) and skin (0.05-0.18% of the dose). Blood, at the 7 d sacrifice, contained 0.26-0.29% of the dose which was localized almost exclusively in the red blood cells. In terms of concentration, only the liver (0.07-0.23 ppm) and red blood cells (0.07-0.10 ppm) of all groups, and the lung (0.12-0.16 ppm) and kidney (0.08- 0.13 ppm) of the intravenous group approached or exceeded levels of radioactivity higher than 0. 1 ppm (dose-adjusted for high dose group D).
The concentration of radioactivity in the liver in comparison with blood levels demonstrated a mean liver to blood ratio of 1.8 to 4.5. Females appeared to demonstrate a slightly higher liver to blood ratio than males. There was no apparent effect of pretreatment of animals for 14 d at 1.25 mg/kg bw on the liver to blood ratio. However, the ratio did appear slightly lower at the high dose level (125 mg/kg bw) compared to the low dose (1.25 mg/kg bw). The tissue to blood ratios in lung and kidneys of iv dosed animals were also significantly greater than unity. The significance of this apparent tissue accumulation is however difficult to interpret since the red blood cells also demonstrated a higher affinity for the test substance derived radioactivity than did plasma. The finding of higher tissue to blood ratios in the lung and kidney following intravenous administration compared to oral administration suggests either a pharmacokinetic effect due to the different routes of administration or that the metabolism is different between these two routes of administration. At this stage the nature of the radioactivity associated with these tissues or the red blood cells is not known.
Details on excretion:
Routes of elimination: The routes of excretion of the test substance-derived radioactivity from the rat were determined for each of the four treatments (single oral low, single oral high, single intravenous low and repeated oral low dose). A preliminary experiment (Group P1) established that expired gases represented an insignificant route of elimination (<0.15% of the dosed was expired in 24 h). Feces was the major route of excretion for all animals in Groups A-D and P1 accounting for 57.7-77.0% of the dose. An additional 10.8-24.3% of the dose was excreted in the urine. Statistically significant differences for excretion in urine were found between males that received the intravenous dose (24.3%) versus the low oral dose (17.0%) and males that received the low dose (17.0%) versus the high dose (13.0%). There were no significant differences in urine excretion between males and females. Statistically significant differences in excretion via the feces were found between males receiving the low oral (66.3%) versus the intravenous low dose (57.7%), females receiving the low oral (65.3%) versus the intravenous dose (59.2%), males receiving the low dose ( 66.3%) versus the high dose (77.0%) and females receiving the low dose (65.3%) versus the high dose (74.2%). Only one statistically significant, but minor, difference between males and females in feces excretion was noted. At the high dose, males excreted 77.0% of the dose in the feces while the females excreted 74.2% of the dose in the feces. Pre-dosing had no effect on routes of excretion.
Biliary excretion: Animals of Group P5 were administered test substance by oral gavage at a dose level of 125 mg/kg, and bile was collected for 48 h. Rats eliminated 31.7 ± 8.9% and 20.5 ± 8.7% of the dose via the bile for males and females, respectively.
Toxicokinetic parametersopen allclose all
Test no.:
#1
Toxicokinetic parameters:
other: Initial (α) phase half-lives for urine and whole body elimination of orally dosed rats were 4.8-8.6 and 5.7-8.5 h, respectively
Test no.:
#1
Toxicokinetic parameters:
other: Terminal (β) phase halflives for plasma, urine and whole body were 45.2-55.8, 41.9-118 and 76.5-111 h, respectively

Metabolite characterisation studies

Metabolites identified:
yes

Bioaccessibility

Bioaccessibility testing results:
Whole-body autoradiography: It was performed on male and female rats and at both the 1.25 and 125 mg/kg bw dose levels. At 24 h following a single gavage dose of approximately 1.25 mg/kg bw, the major areas of localization were the gut contents and liver. For both male and females, the liver had a mottled texture which was very marked, however the liver was much darker in the females. This difference in liver localization between the sexes was constant for both dose levels. The intensities in the tissues were compared using identical exposure periods and development procedures. Other areas of localization were comparable between males and females and included the kidney, heart, lungs, blood, spleen and linings of the tongue and esophagus. At 24 h after dosing, the male had a full stomach with localization of radioactivity in the stomach contents, while the female had an empty stomach and localization in the stomach lining. After 5 d following a single gavage dose of 14C-test substance at the low dose, the most intense area of localization was the liver. The appearance of the liver was similar to that of the 24 h sacrifice animals in that it had a mottled texture and was much darker in the female as compared to the male. Other areas of localization included the kidney, heart, spleen, lungs and blood. A small amount of radioactivity was observed in the gut contents. At 24 h after dosing, at the 125 mg/kg bw dose level, sites of localization were similar to that of the low dose group. The major areas of localization were the liver and intestinal contents. The livers were highly labeled and had a mottled texture. The liver of the female was more labeled than that of the male. Radioactivity was observed in the stomach contents of the male and in the stomach lining of the female. Other areas of localization included the kidney, which was almost as intense as the liver, heart, lungs, blood, spleen and skin. Intense localization was still observed in the liver and kidney of the 7 d sacrifice animals. The livers were mottled and as in previous groups, darker in the females. The kidneys were also highly labeled. Radioactivity was also observed in the heart, lungs, blood, spleen, intestinal contents and nasal turbinates.

Any other information on results incl. tables

Other results:

Dosing data: All animals received a target dose of 1.25 or 125 mg/kg bw. Theadministered doses for animals in groups A-D, P2 and P5 were all withinapprox 10% of the target dose with the exception of two animals in Group Dand one animal in Group P5. For these three animals, the administered dose was somewhat low but within 20% of the target dose. Animals in group H received doses averaging 110 mg/kg bw, approx 10%below the target dose, while animals in groups P1 and P4 received doses averaging 0.92 mg/kg bw, approximately 30% below the target dose. The administered dose for animals in group P3 averaged 1.53 mg/kg bw, approx 20% higher than thetarget dose.

 

Total recovery of the test substance: The individual total recoveries for every animal in groups A-D, P1 and P5 ranged from 85.5-96.0%. The mean total recovery per group ranged from 87.7-95.1%. All animals except the males of group C (repeated oral dose) had individual recoveries of >90%.

 

Pharmacokinetic analysis:

-Blood plasma and blood cells: Animals of group P2 received a single oral low dose of the test substance. The plasma elimination curves for group P2 were generally biphasic. However, the initial (alpha) phase was not well-defined and exhibited complex behavior, especially in the males. Thus, accurate determinations of the alpha phase half-lives (t1/2α) were not possible. The reason for the complexity in the initial clearance profiles for the plasma of group P2 is unknown but may be due to enterohepatic circulation. The mean t1/2β was 45.2±2.5 h (males) and 55.8±5.0 h (females). The mean half-life in blood cells, estimated from the terminal portion of the curve (approx 1-5 d post-dose), was 116±42 h for the males and 140±13 h for the females. Animals of group P3 received a single intravenous low dose of the test substance. Elimination from the blood plasma was consistent with a simple two-compartment model. The mean t1/2α in blood plasma was 0.54±0.11 h (males) and 0.97±0.08 h (females). The meant 1/2β was 26.2±4.7 h (males) and 38.7±5.5 h (females). The mean half-life in blood cells, estimated from the terminal portion of the curve (approx 1-5 d postdose), was 126±14 h (males) and 133±8.3 h.

-Urine: The mean t1/2α in urine ranged from 4.8-8.6 h and thet1/2β in urine ranged from 41.9-118 h for groups A-D in this study. The urine alpha phase half-life appeared to be slightly higher in males than in females. The difference was statistically significant for the oral low dose group (B) (Males: 7.34, Females: 6.06 h) and the preconditioned group (C) (males: 7.18, females: 6.22 h). There were no statistically significant differences in the urinaryt1/2βbetween males and females of groups A-D. Little difference in kinetics was observed between dosing regimes although the urine alpha phase half-life was slightly higher for the low dose oral group (group B) compared to the low dose intravenous group (group A). Comparing dose levels, the beta phase half-life was higher for the high dose group (group D) than the low dose group (group B), but the difference was statistically significant only for the males.

-Whole body: The mean whole body t1/2α ranged from 5.72-8.45 h and the t1/2β ranged from 76.5-111 h for groups A-D. There were no significant differences between males and females within the same group. The mean t1/2α was significantly greater for the male rats dosed orally (7.88 h) versus intravenously (5.72 h), the female rats dosed orally (8.45 h) versus intravenously (5.74 h), and significantly greater for females receiving a single oral low dose (8.45 h) versus females receiving repeated oral low doses (7.41 h). The meant 1/2 β was significantly greater for both males and females receiving the single oral low dose (111 and 100 h, respectively) versus males and females receiving the single low intravenous dose (86.2 and 76.5 h, respectively).

-Bile: Although the average curves, especially for males, are reasonably linear, there was wide variation in the individual animal curves. Most of them were far from linear. The half-life for biliary excretion was estimated from the average curves to be 8-9 h for both males and females.

Applicant's summary and conclusion

Conclusions:
MON 13900 appears to be extensively absorbed and rapidly eliminated with elimination occurring primarily via the feces. No tissue level accounted for more than one percent of the dose and only the liver (oral and intravenous), lung (intravenous, only) and kidney (intravenous, only) demonstrated any evidence of accumulation as reflected by tissue to blood ratios greater than one. However, the nature of the blood cell and tissue associated radioactivity is unknown. In addition, the total radioactivity associated with the tissues and carcass accounted for less than 1.7% of the administered dose. Females demonstrated slightly higher tissue levels (liver, lung and kidney) than males and there was no significant effect of dose level or pretreatment with MON 13900.
Executive summary:

A pharmacokinetics and metabolism study of MON 13900 (furilazole) was conducted in rats according to EPA OPP 85-1 Guideline in compliance with GLP.

 

Young adult male and female Sprague-Dawley rats received either single or repeat oral gavage doses, or intravenous doses of the test substance labeled with carbon-14 in the 4-position (methylene carbon) of the oxazolidine ring. The oral doses were administered at 1.25 or 125 mg/kg bw in Emulphor EL-620 and the intravenous doses were administered at 1.25 mg/kg bw in Emulphor:ethanol:saline (1:1:8 v/v). The study consisted of six preliminary experiments (groups P1-P5 and H) designed to determine CO2expiration, blood plasma concentration after oral and intravenous administration, tissue distribution by whole body autoradiography and biliary excretion, and a definitive study consisting of four groups (single intravenous low dose, single oral low dose, repeat oral low dose and single oral high dose). 

 

Total recovery for all groups of animals ranged from 87.7 to 95.1% of the dose. The feces represented the major route of elimination accounting for approx 58 to 77% of the dose. Urine accounted for approx 11 to 24% of the dose (groups P1 and A-D). Expired gases, collected for 24 h after dosing, contained only 0.11-0.13% of the dose. The radioactivity associated with the residual carcass, excluding the tissues removed at necropsy, accounted for a maximum of 0.56% of the administered dose at 7 d after dosing. The tissues collectively (including blood and gut contents) contained 0.52-1.12% of the dose. Thus, the total radioactivity remaining in the rat (tissues, blood, gut contents and carcass) constituted a maximum of 1.65% of the dose at 7 d after dosing. The extent of absorption was determined by comparison of urinary excretion between orally dosed rats and the intravenously dosed rats. Absorption following administration of 14C-test substance at the low oral dose and repeated low oral dose was approx 70% and 68.5%, respectively, for males, and 83% and 85%, respectively, for females. Absorption at the high dose level was lower and was approx 54% and 66% for males and females, respectively. Thus, there appeared to be some dose dependency on the extent of absorption. Also, females demonstrated a higher percent absorbed than the males. Analysis of the rate of excretion of radioactivity in the urine revealed a biexponential elimination process with a half-life for the initial phase of approx 4.8-8.6 h and for the terminal elimination phase of 41.9-118 h. Determination of whole body elimination revealed similar elimination rates. Excretion was rapid with greater than 80% of the dose eliminated within 48 h. Analysis of tissue distribution at 7 d after dosing demonstrated generally low levels of radioactivity in most tissues, with no tissue accounting for more than 1% of the dose. The liver was the only tissue that showed any evidence of significant amounts of radioactivity following oral administration accounting for 0.33-0.88% of the dose. The only other tissues which exceeded 0.1% of the dose in any group were kidney (0.06-0.11% for the intravenous dose, 0.02-0.03% for the oral doses), muscle (0.09-0.18% of the dose) and skin (0.05-0.18% of the dose). Blood, at the 7 d sacrifice, contained 0.26-0.29% of the dose which was localized almost exclusively in the red blood cells. In terms of concentration, only the liver (0.07-0.23 ppm) and red blood cells (0.07-0.10 ppm) of all groups, and the lung (0.12-0.16 ppm) and kidney (0.08-0.13 ppm) of the intravenous group approached or exceeded levels of radioactivity higher than 0. 1 ppmn (dose adjusted for high dose group D). The concentration of radioactivity in the liver, in comparison with blood levels, demonstrated a liver to blood ratio of 1.8 to 4.5. Only the liver and red blood cells of all groups, and the lung and kidney of the intravenous group, had tissue to blood ratios significantly greater than one. Liver to blood ratios were slightly higher in the females compared to the males. In contrast, blood levels were comparable between the sexes. There was no significant effect of pretreatment of animals for 14 d at 1.25 mg/kg bw on the liver to blood ratio. However, the ratio did appear slightly lower at the high dose level (125 mg/kg bw) compared to the low dose (1.25 mg/kg bw). It was found that following intravenous administration the tissue to blood ratios in lung and kidney were greater than unity, and significantly different than those observed following oral administration. The finding of higher tissue to blood ratios in the lung and kidney following intravenous administration, compared to oral administration, suggests either a pharmacokinetic or metabolic effect due to the different routes of administration. Repeated dosing, on the other hand, appeared to have no significant effect on tissue accumulation nor was there any significant effect of dose level on tissue distribution or tissue levels. The significance of these higher tissues to blood ratios in the lungs and the kidneys, which are highly-perfused organs, is difficult to interpret since the red blood cells also demonstrated a higher affinity for the test substance-derived radioactivity than did plasma. At this stage, the nature of the radioactivity associated with these tissues or the red blood cells is not known. The overall tissue distribution was also studied by whole body autoradiography which confirmed that the liver contained higher levels of radioactivity than other tissues at sacrifice. Whole body autoradiography also confirmed the higher liver levels in females compared to males at both the low and high dose levels. Low levels of radioactivity were observed in the highly perfused organs (heart, kidney, lung and spleen), blood and the gastrointestinal tract, as well as the nasal turbinates (high dose only). No other significant localization of radioactivity was observed.

 

In conclusion, the test substance appears to be well absorbed and rapidly eliminated with elimination occurring primarily via the bile into feces. No tissue level accounted for more than one percent of the dose and only the liver (oral and intravenous), lung (intravenous, only) and kidney (intravenous, only) demonstrated any evidence of accumulation as reflected by tissue to blood ratios significantly greater than one. In addition, the total radioactivity associated with the tissues and carcass accounted for less than 1.7% of the administered dose. Females demonstrated slightly higher tissue levels (liver, lung and kidney) than males and there was no significant effect of dose level or pretreatment with the test substance. The nature of the blood cell and tissue associated radioactivity is unknown. However, as mentioned, this data should be interpreted with caution in view of the apparent affinity of the test substance-derived radioactivity for red blood cells.