Reaction mass of 1,3-diacetoxypropan-2-yl 12-acetoxyoctadecanoate and 2,3-diacetoxypropyl 12-acetoxyoctadecanoate

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2003-07-31 to 2003-08-18

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study performed in accordance with GLP regulations

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Cross-reference 2

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2004

Report date:

2004

Materials and methods

Objective of study:

toxicokinetics

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

no

Principles of method if other than guideline:

NA

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

-

EC Number:

451-530-8

EC Name:

-

Cas Number:

736150-63-3

Molecular formula:

Not applicable

IUPAC Name:

1,3-bis(acetyloxy)propan-2-yl 12-(carboxyoxy)octadecanoate; 2,3-bis(acetyloxy)propyl 12-(acetyloxy)octadecanoate

Details on test material:

Unlabelled TS-ED 532
Name of test material: TS-ED 532
- Lot/batch No.: batch 10102
- Expiration date of the lot/batch: 2003-11-22

Radiolabelled TS-ED 532
Identity: 12-[1-14C]acetoxy-octadecanoic acid-2,3-diacetoxy-propyl ester
Description: Clear liquid
Lot No.: 2329/51
Specific Activity: 1.016 mCi/g (37.6 MBq/g) (calculated)
Radiochemical Purity: 96.7% (measured at CTBR)
Storage Conditions: Room temperature, light (out of direct light)
Expiry Date: August 1, 2004


The specific activity of the radiolabelled test article was measured at CTBR before administration of the dose using a gravimetric method and liquid scintillation spectroscopy. The radiochemical purity of radiolabelled TS-ED 532 was measured at CTBR before administration of the dose, using TLC (method supplied by the Sponsor) with radiochemical detection by phosphor-imaging. The radiochemical purity is the percent of the total radioactivity associated with radiolabelled TS-ED 532.

Radiolabelling:

yes

Remarks:

12-[1-14C]acetoxy-octadecanoic acid-2,3-diacetoxy-propyl ester

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Sprague-Dawley rats (Crl:CD (SD) BR)
- Age at study initiation: 8 to 10 weeks of age
- Weight at study initiation: 260 to 362 g.
- Fasting period before study: no information
- Housing: individually in stainless steel wire meshbottomed cages equipped with an automatic watering valve
- Individual metabolism cages: yes
- Diet (e.g. ad libitum): certified commercial laboratory diet (Harlan Teklad #8728CM) ad libitum
- Water (e.g. ad libitum): municipal tap water ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3°C
- Humidity (%): 50 ± 20%
- Photoperiod (hrs dark / hrs light): 12 hours light and 12 hours dark

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

unchanged (no vehicle)

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:

DIET PREPARATION
- Unlabelled TS-ED 532 was administered at a target dose level of 500 mg/kg bw (0.5 mL/kg bw) for group 2 and at a target dose level of 5000 mg/kg bw (5 mL/kg bw) for groups 3 and 4.

Radiolabelled TS-ED 532 was added to unlabelled TS-ED 532 in order to achieve a target radioactivity level of 10 µCi/animal of 12-[1-14C]acetoxy-octadecanoic acid-2,3-diacetoxy-propyl ester.

Before and after dosing, the radioactivity concentration of the dose formulation was analyzed at CTBR by liquid scintillation spectroscopy. Triplicate 50 µL aliquots of the dose formulation were diluted in 1 mL of unlabelled TS-ED 532. Then duplicate 100 µL aliquots of each dilution were weighed in glass scintillation vials and mixed with approximately 10 mL of liquid scintillation fluid (Hionic Fluor, Packard). The specific activity of test article in the dose formulation was calculated by the following equation:

Specific activity, dpm/mg = A/B

A = Mean radioactivity concentration (dpm)/g of the dose formulation measured prior to and after the end of treatment.

B = Concentration of test article (mg/g), based on weight of unlabelled and radiolabelled test articles in the dose formulation.

The specific activity of the combined unlabelled and radiolabelled TS-ED 532 in the dose formulation were calculated to be 101.80 x 106 dpm/g for group 2 and 8.35 x 106 dpm/g for group 3 and 4.

VEHICLE
- Justification for use and choice of vehicle (if other than water): NA
- Concentration in vehicle: NA
- Amount of vehicle (if gavage): NA
- Lot/batch no. (if required): NA

HOMOGENEITY AND STABILITY OF TEST MATERIAL: TS-ED 532 was assessed to be homegenous and stable in the period of testing.

Duration and frequency of treatment / exposure:

Group 2 animals were administered unlabelled test article daily for five days by oral gavage at a target dose level of 500 mg/kg in a dose volume of 0.5 mL/kg. On the following day, a single formulated dose of 14C-labelled test article was administered by oral gavage at a target dose level of 500 mg/kg in a dose volume of 0.5 mL/kg to deliver a target radioactivity level of 10 Ci/animal. For six days following the radiolabelled dose, the remaining animals were administered unlabelled test article by oral gavage at a target dose level of 500 mg/kg in a dose volume of 0.5 mL/kg.

Group 3 and 4 animals were administered unlabelled test article daily for five days by oral gavage at a target dose level of 5000 mg/kg in a dose volume of 5 mL/kg. On the following day, a single formulated dose of 14C-labelled test article was administered by oral gavage at a target dose level of 5000 mg/kg in a dose volume of 5 mL/kg to deliver a target radioactivity level of 10 Ci/animal. For six days following the radiolabelled dose, remaining Group 3 animals were administered unlabelled test article by oral gavage at a target dose level of 5000 mg/kg in a dose volume of 5 mL/kg. Group 4 animals were administered unlabelled test article by oral gavage at a target dose level of 5000 mg/kg; in a dose volume of 5 mL/kg for only two days following the radiolabelled dose.

Doses / concentrations

Remarks:

Doses / Concentrations:
500 mg/kg in a dose volume of 0.5 mL/kg for group 2

5000 mg/kg in a dose volume of 5 mL/kg for groups 3 and 4.

Radiolabelled TS-ED 532 was added to unlabelled TS-ED 532 in order to achieve a target radioactivity level of 10 µCi/animal.

No. of animals per sex per dose / concentration:

Group 1: one male rat (No 1001)
Group 2: twenty-four male rats (No 2001-2024)
Group 3: twenty-four male rats (No 3001-3024)
Group 4: five male rats (4001-400), (4006-4010*)

*Due to a technical error during the study a new group of five rats was added to the study as replacements, identified as No 4006-4010.

Control animals:

yes, concurrent no treatment

Positive control reference chemical:

No positive control group was included

Details on study design:

- Dose selection rationale: The purpose of this study was to determine and compare the concentration and content of radioactivity in blood, plasma and tissues in Sprague-Dawley rats following a single oral gavage dose of 12-[1-14C]acetoxy-octadecanoic acid-2,3-diacetoxy-propyl ester administered during a 12-day oral gavage regime using unlabelled TS-ED 532. Disposition kinetics, excretion and mass balance of radioactivity was also determined.

Two groups (groups 2 and 3) of twenty-four male Sprague-Dawley rats that were approximately 8 to 10 weeks of age and a group (group 4) of five male Sprague-Dawley rats that were approximately 7 to 8 weeks of age received unlabelled TS-ED 532 daily for five days. On the sixth day, group 2 animals received a single dose of 12-[1-14C]acetoxy-octadecanoic acid-2,3-diacetoxy-propyl ester by oral gavage at a target dose level of 500 mg/kg in a dose volume of 0.5 mL/kg. Group 3 and 4 animals received a single dose of 12-[1-14C]acetoxy-octadecanoic acid-2,3-diacetoxy-propyl ester by oral gavage at a target dose level of 5000 mg/kg in a dose volume of 5 mL/kg bw. For six days following the radiolabelled dose, the remaining group 2 and 3 animals unlabelled TS-ED 532. Group 4 animals received unlabelled TS-ED 532 for only two days following the radiolabelled dose.

Blood, plasma and tissue samples were collected at selected time points up to 168h post radiolabelled dose from 3 animals/time point from groups 2 and 3.

Group 4 animals were housed in metabolic cages and urine faces and expired 14CO2 were collected at selected time points up to 72h post radiolabelled dose.

- Rationale for animal assignment (if not random): NA

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, serum or other tissues, adipose tissue (perirenal), gastrointestinal tract (GIT) and contents, kidneys and adrenals, liver and thymus.

- Time and frequency of sampling: Terminal blood samples were collected at 1, 3, 6, 12, 24, 48, 72 and 168 hours post radioactive dose from 3 animals/time point from groups 2 and 3. Samples were collected by exsanguination from the abdominal aorta of rats (groups 1, 2 and 3) euthanized under isoflurane anaesthesia.

Following exsanguination, the following tissues were collected at the same time points mentioned above for blood sampling from 3 animals/time points from groups 2 and 3: Adipose tissue (perirenal), gastrointestinal tract (GIT) and contents, kidneys and adrenals, liver and thymus.

Remaining carcasses were collected from animals killed at 12, 24, 48 and 72 hours only. All other remaining carcasses were discarded. All tissues mentioned above as well as blood, plasma and remaining carcass were also collected from one group 1 animal to determine background radioactivity.

Urine and faeces were collected on dry ice from the group 4 animals (animal 4006 to 4010) at the following sampling time points: 6, 12, 24, 48 and 72 hours post radiolabelled dose.

Expired 14C-CO2 was collected by drawing the cage air through a single collection tower containing circa 300 mL of 4N KOH at a target flow rate of 500-600 mL/min. Moisture and CO2 were removed from the air drawn through the cage by columns of anhydrous calcium chloride. The 14C-CO2 trapping solutions were collected at the following sampling time points: 3, 6, 12, 24, 48 and 72 hours post radiolabelled dose.

Cages were rinsed with deionized water at 72 hours post dose. At 72 hours after dosing, the animals were euthanized by Euthanyl injection and the carcasses were retained for analysis.

Urine, faeces and expired 14C-CO2 were collected at 6, 12 and 24 hours post radiolabelled dose from the initial group 4 animals (animal 4001 to 4005) and represented defined time points prior to pump failure.

The blood, plasma and tissues collected from group 1 animal were used for the determination of background radioactivity level. Pre-dose urine and faecal samples from one group 4 animal were used to determine background radioactivity levels. Deionized water was used to determine background radioactivity levels for the cage rinses.

Statistics:

Numerical data obtained during the conduct of the study were subjected to calculation of group mean values and standard deviations

Results and discussion

Preliminary studies:

NA

Main ADME results

Main ADME results 1

Type:

absorption

Results:

Uptake of radioactivity into the systemic circulation was rapid with a peak concentration in blood occurring between 1 and 3 hours post-dosing at 500 mg/kg and at 6 hours post-dosing at 5000 mg/kg.

Main ADME results 2

Type:

distribution

Results:

Maximum concentrations in the tissues include liver (1.29% of the dose) at 24 hours post-dosing, kidneys (0.23% of the dose) at 6 hours post-dosing, and thymus (0.026% of the dose) at 12 hours post-dosing.

Main ADME results 3

Type:

metabolism

Results:

Metabolism is expected to be relatively rapid and consist of extensive hydrolytic cleavage of the 12-acetyl function followed by catabolism of the acetate to CO2.

Main ADME results 4

Type:

excretion

Results:

Elimination of radioactivity from the blood was slow at both doses. The mean plasma elimination half-life time was 55.6 hours at 500 mg/kg and 51.9 hours at 5000 mg/kg. Radioactivity was eliminated from the body as 14C-CO2.

Toxicokinetic / pharmacokinetic studies

Details on absorption:

The mean observed blood and plasma radioactivity concentration profiles between group 2 and group 3 animals differed substantially. In group 2, blood and plasma radioactivity concentrations decreased rapidly from approximately 106.1 µg eq/mL and 138.1 µg eq/mL at 1 h to 15.2 µg eq/mL and 5.3 µg eq/mL at 168 h post treatment, respectively. In group 3, blood and plasma radioactivity concentrations rose from approximately 253.4 µg eq/mL and 300.7 µg eq/mL at 1 h to maximum concentrations of 434.0 µg eq/mL and 672.4 µg eq/mL at 6 h post treatment, respectively. Thereafter, blood and plasma levels declined to 118.6 µg eq/mL and 40.5 µg eq/mL at 168 h, respectively.

Blood to plasma ratios in group 2 and group 3 animals were similar and lower than 1 (0.6 to 0.8) up to 24 h post dose indicating that little radioactivity was associated with blood cells. From the 48 h time point, the ratios increased over the study interval, indicating a faster clearance from plasma than from blood. For group 2 animals, the percent of dose in blood was estimated to be approximately 1.3% at 1 h post dose. Subsequently, levels decreased to 0.2% at the last collection time point of 168 h. For Group 3 animals, the percent of dose in blood was estimated to be approximately 0.3% at 1 h post dose. The levels then rose gradually up to 0.6% and declined to 0.2% at the last collection time point of 168 h.

Details on distribution in tissues:

Following oral administration of 12-[1-14C]acetoxy-octadecanoic acid-2,3-diacetoxy-propyl ester, the highest radioactivity concentration in the tissues analyzed was observed at 1 h post treatment in the gastrointestinal tract and contents at approximately 2922 µg eq/g and 44050 µg eq/g for group 2 and 3 animals, respectively. These levels decreased over the course of the study to 12 µg eq/g and 122 µg eq/g for group 2 and 3 animals, respectively, representing both excretion of TS-ED 532 from the GIT contents and absorption of TS-ED 532 into the systemic circulation.

From the 48 h time point, the liver, the kidneys and adrenals and the thymus showed higher radioactivity concentrations than GIT and contents in both groups. For group 2 animals, the radioactivity concentrations in these tissues gradually declined over the 168 h period post-dose. For group 3 animals, the kidneys and adrenals, thymus and liver reached maximum concentrations at the 6 h, 12 h and 24 h time point, respectively, and then declined for the rest of the observation period.

The radioactivity concentrations in adipose tissue (perirenal fat) increased from the 24 h time point throughout the study in group 2 and from the 12 h time point to the 72 h time point in group 3. The radioactivity concentrations in adipose tissue (perirenal fat) then decreased until the 168 h time point for group 3 animals. At this last time point, the radioactivity concentration in adipose tissue (perirenal fat) for animals 3023 and 3024 could not be reported since the values measured were inconsistent and could not be reproduced.

The highest tissue to plasma ratio was observed at 1 h post treatment in the gastrointestinal tract and contents at approximately 23 and 152 for group 2 and 3 animals, respectively. Due to excretion of TS-ED 532 from the GIT contents, this ratio decreased rapidly over the course of the study to 2.4 for both groups at 168 h post dose. For kidneys and adrenals, the tissue to plasma ratio decreased from the 3 h time point to the 12 h time point in both groups. For most other tissues in both groups, the tissue to plasma ratios increased during the course of the study indicating a faster clearance from plasma than tissues. The lowest tissue to plasma ratios were observed in the adipose tissue (perirenal fat) of both groups.

The highest percentage of dose in tissues was observed in the GIT and contents at 1 h post dose for group 2 at approximately 50% and at 3 h post dose for group 3 at approximately 81% as expected since TS-ED 532 was administered by gavage. Due to excretion and absorption of TS-ED 532, the percent of dose in the GIT and contents decreased rapidly over the course of the study to 0.2% and 0.3% for group 2 and 3 animals, respectively, at 168 h post dose.

The percent of dose in the carcasses was similar and constant for both groups at the selected time points (12 h, 24 h, 48 h and 72 h post dose) indicating that TS-ED 532 may have been distributed in other tissues than the ones selected for analysis. Group 2 values ranged from 8.3% to 4.9% and Group 3 values ranged from 7.2% to 5.4%. For group 2, the percentage of dose in the liver was 2.5% at 1 h post dose and decreased throughout the study to 0.2%. The percentage of dose in all other tissues for both groups was less than 1.5%. The lowest percentage of dose was found in the adipose tissue (less than 0.018%).

Transfer into organs

Transfer type:

other: From the 48 h time point, the liver, the kidneys and adrenals and the thymus showed higher radioactivity concentrations (in g eq/g) than GIT and contents in both groups (2 and 3).

Observation:

other: Maximum concentrations in the tissues included liver (1.29% of the dose) at 24 hours post-dosing, kidneys (0.23% of the dose) at 6 hours post-dosing, and thymus (0.026% of the dose) at 12 hours post-dosing.

Details on excretion:

In Group 4, the mean total recovery of radioactivity in the excreta of the 72 h period post dose was 108.5% of the dose (urine, 6.5%; feces, 24.6%; CO2, 77%; and cage wash, 0.5%). Most of the recovered radioactivity (97.5%) was excreted by 24 h post dose. The data demonstrated that the greatest amount of radioactivity was eliminated via the expired air, with some excretion via the feces. Little radioactivity was eliminated via the urine. The mean mass balance of radioactivity at 72 h post-dose was 115% (ranging from 112% to 118%) with approximately 6.7% in the remaining carcass. The recovery was considered good.

Toxicokinetic parameters

Toxicokinetic parameters 1

Toxicokinetic parameters:

half-life 1st: Mean t½ (h) for Group 2 (500 mg/kg/day): 55.6

Toxicokinetic parameters 2

Toxicokinetic parameters:

half-life 1st: Mean t½ (h) for Group 3 (5000 mg/kg/day): 51.9

Toxicokinetic parameters 3

Toxicokinetic parameters:

AUC: Mean AUC0-168h (g eq·h/g) for Group 2 (500 mg/kg/day): 4384

Toxicokinetic parameters 4

Toxicokinetic parameters:

AUC: Mean AUC0-168h (g eq·h/g) for Group 3 (5000 mg/kg/day): 33799

Toxicokinetic parameters 5

Toxicokinetic parameters:

Cmax: Mean Cmax (g eq/g) for Group 2 (500 mg/kg/day): 138

Toxicokinetic parameters 6

Toxicokinetic parameters:

Cmax: Mean Cmax (g eq/g) for Group 3 (5000 mg/kg/day): 672

Toxicokinetic parameters 7

Toxicokinetic parameters:

Tmax: Mean tmax (h) for Group 2 (500 mg/kg/day): 1

Toxicokinetic parameters 8

Toxicokinetic parameters:

Tmax: Mean tmax (h) for Group 3 (5000 mg/kg/day): 6

Toxicokinetic parameters 9

Toxicokinetic parameters:

other: Mean tlast(h) for Group 2 (500 mg/kg/day): 168 h

Toxicokinetic parameters 10

Toxicokinetic parameters:

other: Mean tlast(h) for Group 3 (5000 mg/kg/day): 168 h

Toxicokinetic parameters 11

Toxicokinetic parameters:

other: Mean kel (h-1) for Group 2 (500 mg/kg/day): 0.0125

Toxicokinetic parameters 12

Toxicokinetic parameters:

other: Mean kel (h-1) for Group 3 (5009 mg/kg/day): 0.0134

Metabolite characterisation studies

Metabolites identified:

no

Details on metabolites:

NA

Any other information on results incl. tables

Body weight and dose characterization:

The mean body weights of groups 2, 3, and 4 on the day prior to radiolabelled dosing were 357 g, 346 g and 311 g, respectively. The mean radioactivity concentrations of 12-[1-14C]acetoxyoctadecanoic acid-2,3-diacetoxy-propyl ester dose formulations were 101.80 x 106 dpm/g (45.86 Ci/g) for group 2 and 8.35 x 106 dpm/g (3.76 Ci/g) for groups 3 and 4. The actual mean formulated 12-[1-14C]acetoxy-octadecanoic acid-2,3-diacetoxy-propyl ester dose administered to group 2, 3, and 4 animals was 516 mg/kg, 5015 mg/kg and 5063 mg/kg, respectively. The mean ¹⁴C-radioactivity administered was: Group 2, 8.45 Ci/animal, Group 3, 6.52 Ci/animal and group 4, 5.93 Ci/animal. The slightly lower than targeted levels (10 Ci/animal) administered to animals was considered not to impact on the outcome of the study since rats were dosed similar amounts of labelled and unlabelled test articles per kg of body weight.

Clinical observations:

No treatment related clinical signs were observed in animals prior to or subsequent to treatment with 12-[1-14C]acetoxy-octadecanoic acid-2,3-diacetoxy-propyl ester administered during a 12-day oral gavage regime using unlabelled TS-ED 532.

Detailed disposition kinetics of radioactivity in blood and plasma and tissues:

The areas under the radioactivity concentration vs. time curves (AUC) were calculated from 0 to the last time point. Whenever possible, the AUCs were calculated from zero to infinity. For blood and certain tissues, there were insufficient data points to establish the elimination phase of the curves and thus allow the estimation of kel, half-life time and AUCs from zero to infinity with an acceptable degree of confidence.

For Group 2 animals, radioactivity concentration in blood and plasma reached its maximum (Cmax) at 1 h post dose (tmax). The Cmax values were 106 µg eq/g and 138 µg eq/g for blood and plasma, respectively. The mean AUC(0-tlast) values for blood and plasma radioactivity were also similar. The blood value was calculated as 4506 µg eq·h/g and the plasma value was calculated as 4384 µg eq·h/g. The elimination rate constant, kel, for plasma was calculated as 0.0125 h-1, the t1/2 was 55.6 h and the AUC(0-inf) was 4812 µg eq·h/g.

In group 2, the tmax in tissues was usually observed within 3 h post dose with the exception of the adipose tissue (perirenal fat) for which the tmax was observed at 12 h post dose. The highest Cmax and AUC(0-tlast) values were observed in the gastrointestinal tract and contents at 2922 µg eq/g and 15 594 µg eq·h/g, respectively. Of the other organs, kidneys and adrenals had the highest Cmax and AUC(0-tlast) values (338 µg eq/g and 13 449 µg eq·h/g, respectively) followed closely by liver (332 µg eq/g and 13 234 µg eq·h/g, respectively). In general, the half-life time values for the tissues ranged from 43 to 75 h and the elimination constant values ranged from 0.00928 to 0.0162 h-1.

For group 3 animals, radioactivity concentration in blood and plasma reached its maximum (Cmax) at 6 h post dose (tmax). The Cmax values were 434 µg eq/g and 672 µg eq/g for blood and plasma, respectively. The mean AUC(0-tlast) value was 34 392 µg eq·h/g for blood and 33 799 µg eq·h/g for plasma. The elimination rate constant, kel, for plasma was calculated as 0.0134 h-1, the t1/2 was 51.9 h and the AUC(0-inf) was 36 833 µg eq·h/g.

The tmax in tissues varied considerably between tissues in group 3. The tmax of gastrointestinal tract was observed after 1 h while it took 72 h for the adipose tissue (perirenal fat) to reach maximum concentration. The highest Cmax and AUC(0-tlast) values were observed in the gastrointestinal tract and contents at 44 050 µg eq/g and 515 329 µg eq·h/g, respectively, followed by liver, kidneys and adrenals, thymus and adipose tissue (perirenal fat). The elimination rate constant, kel, for gastrointestinal tract and contents was calculated as 0.0112 h-1, the t1/2 was 61.6 h and the AUC(0-inf) was 526 183 µg eq·h/g.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results
The metabolism and toxicokinetics of TS-ED 532 were investigated using 12-[1-14C]acetoxy-octadecanoic acid-2,3- diacetoxy-propyl ester. Uptake of radioactivity into the systemic circulation was rapid with a peak concentration (representing <2% of the dose) in blood occurring within 6 hours post-dosing. Elimination of radioactivity from the blood was slow at both doses. The mean plasma elimination half-life was between 51.9-55.6 hours. Radioactivity was eliminated
from the body as 14C-CO2 with 62% accounted for within 12 hours of dosing, 70.8% within 24 hours and 77% after 72 hours. The remaining radioactivity was excreted in urine (6.5%) and faeces (24.6%). Metabolism is expected to be rapid with extensive hydrolytic cleavage of the 12-acetyl function from labelled TS-ED 532 and subsequent catabolism of the majority of the released 14-C labelled acetate to 14C-CO2.

Executive summary:

The metabolism and toxicokinetics of TS-ED 532 were investigated according to OECD Guideline 417. No treatment related clinical signs were observed. Uptake of radioactivity into the systemic circulation was rapid with a peak concentration in blood occurring between 1 and 3 hours post-dosing at 500 mg/kg and at 6 hours post-dosing at 5,000 mg/kg. The peak concentration represented approximately 1.2 to 1.3% of the administered dose at 500 mg/kg and approximately 0.56% of the dose at 5000 mg/kg. Elimination of radioactivity from the blood was slow at both doses. The mean plasma elimination half-life was 55.6 hours at 500 mg/kg and 51.9 hours at 5,000 mg/kg. Radioactivity was eliminated from the body as¹⁴CO₂with 62% accounted for within 12 hours of dosing, 70.8% within 24 hours and 77% after 72 hours. The remaining radioactivity was excreted in urine (6.5%) and faeces (24.6%). Maximum concentrations in the tissues include liver (1.29% of the dose) at 24 hours post-dosing, kidneys (0.23% of the dose) at 6 hours post-dosing, and thymus (0.026% of the dose) at 12 hours post-dosing.

Metabolism is expected to be relatively rapid and consist of extensive hydrolytic cleavage of the 12-acetyl function then catabolism of the acetate to CO₂. The recovery of a substantial proportion of the administered radioactivity as¹⁴CO₂suggests that deacylation may be initiated in the stomach and that there is no significant absorption of unchanged TS-ED 532