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Link to relevant study record(s)

Reference
Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
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
metabolism
Species:
other: rat and mouse
Strain:
other: F344/N and B6C3F1
Sex:
male/female
Details on test animals and environmental conditions:
Summarized data for all three toxicokinetic studies: Single-administration intravenous and gavage study, gavage study in core study animals and single-dose toxicokintec study in aged animals:
TEST ANIMALS
- Source: Taconic Laboratory Animals and Services (Germantown, NY) and Charles River Laboratories (Portage, MI)
- Housing: Polycarbonate cages and hardwood bedding
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum):ad libitum
- Acclimation period: 11 days to 14 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): about 22°C
- Humidity (%): about 50%
- Air changes (per hr): minimum of 10/hour
- Photoperiod (hrs dark / hrs light): 12 hours/day
Route of administration:
other: oral gavage or intravenous
Vehicle:
methylcellulose
Duration and frequency of treatment / exposure:
PREPARATION OF DOSING SOLUTIONS:
- Single-administration intravenous and gavage study: Dose formulations for gavage administration were prepared in 0.5% aqueous methylcellulose. Dose formulations for intravenous injection were prepared by mixing methyleugenol with water:emulphor:ethanol (8:1:1). Dosing volume=4 mL/kg body weight (intravenous injection); Dosing volume=10 mL/kg body weight (gavage).
- Gavage study in core study animals and single-dose toxicokintec study in aged animals: The dose formulations were prepared by mixing methyleugenol with 0.5% aqueous methylcellulose to give the required concentrations. Dosing volume=5 mL/kg body weight (rats); Dosing volume=10 mL/kg body weight (mice)


VEHICLE
- Concentration in vehicle: 0.5% aqueous methylcellulose (for all three studies)
- Lot/batch no. (if required): 876672 and 946150 (only 876672 used in the single-administration intravenous and gavage study)
- Purity: USP/FCC grade (for all three studies)
Duration and frequency of treatment / exposure:
- Single-administration intravenous and gavage study: single dose
- Gavage study in core study animals: 5 days a week for 18 months
- Single-dose toxicokintec study in aged animals: 18 month undosed animals received a single dose
Remarks:
Doses / Concentrations:
- Single-administration intravenous and gavage study: Intravenous injection of 37 mg methyleugenol/kg body weight; single dose of 37, 75, or 150 mg methyleugenol/kg body weight by gavage (rats) and a single intravenous injection of 25 mg methyleugenol/kg body weight or a single dose of 25, 50, or 75 mg methyleugenol/kg body weight by gavage (mice)
- Gavage study in core study animals: Administration of 37, 75, 150, or 300 mg/kg (rats) and administration of 37, 75 or 150 mg/kg (mice)
- Single-dose toxicokintec study in aged animals: Dose of 75 mg/kg (mice) or 150 mg/kg (rats)
No. of animals per sex per dose:
- Single-administration intravenous and gavage study: 12 male and 12 female rats; 24 male and 24 female mice
- Gavage study in core study animals: 10 male and 10 female rats and 10 male and 10 female mice
- Single-dose toxicokintec study in aged animals: 14 male and 15 female rats and 12 male and 14 female mice
Details on absorption:

Absorption (rats):
Absorption from oral doses was rapid, with peak plasma levels achieved within the first 5 minutes for all doses in males and females.

Absorption (mice):
Absorption from oral doses was rapid, with peak plasma levels achieved within the first 5 minutes for all doses in males and females.
Details on distribution in tissues:
Distribution (rats):
Methyleugenol and its metabolites were distributed preferentially to the liver 72 hours after gavage or intravenous administration of [14C]-methyleugenol to males. Tissue:blood ratios of methyleugenol-derived radioactivity were 2 to 3 in the liver, 0.9 to 1.4 in the kidney, and significantly less than 1 in all other tissues examined after 72 hours.

Distribution (mice):
Methyleugenol and its metabolites were distributed preferentially to the ovaries, stomach, fat, spleen, and liver 72 hours after oral administration of [14C]-methyleugenol to males. Tissue:blood ratios of methyleugenol-derived radioactivity were approximately 5 in the liver, 5 to 9 in the stomach, 7 in the fat and the spleen, and over 100 in the ovaries after 72 hours. Many other tissues had elevated ratios; this may represent residual binding of metabolites rather than tissue solubility.
Details on excretion:

Elimination (rats):
Approximately 85% of methyleugenol administered orally to males was eliminated in urine as parent or metabolites. Elimination of methyleugenol from the bloodstream was rapid and multiphasic, with initial half-lives on the order of 5 minutes and terminal half-lives on the order of 1 to 2 hours in males and females. No difference in the elimination of the parent compound between naive males and females was apparent with either young or aged animals. Male core study animals eliminated methyleugenol more rapidly at 6 and 12 months, with areas under the concentration versus time curve (AUCs) generally less than those for the naive animals. Females at all time points and males at 18 months had AUCs similar to those of naive animals. This suggests that metabolic induction may occur to a greater extent in males than in females. Plots of AUC versus dose were sublinear in males at 6 and 12 months, indicative of metabolic saturation at the higher doses at these time points, but approximately linear at 18 months. The increase in AUCs with age in the core study males and females is suggestive of an age-related decrease in methyleugenol metabolic capability.

Elimination (mice):
Elimination of methyleugenol from the bloodstream was rapid and multiphasic, with terminal half-lives in the order of 15 to 30 minutes. No difference in the elimination of methyleugenol between naive males and females was apparent with either young or aged animals. Aged females exhibited a significantly higher AUC; this may be due to differences in the amount of body fat or an age-related decrease in metabolic capability. Core study animals eliminated methyleugenol with AUCs similar to those of the naive animals. Exceptions were for the low-dose females. The AUCs increased linearly with dose in females at 12 months and sublinearly in males at 12 months. The latter finding is indicative of metabolic saturation at the higher doses in males at this time point.
Metabolites identified:
yes
Details on metabolites:
Metabolism (rats):
Methyleugenol was rapidly metabolized. Approximately 85% of methyleugenol orally administered to males was eliminated in urine as metabolites by 72 hours after dosing. Bioavailability of methyleugenol was low in both males and females, with less than 6% bioavailability at 37 mg/kg. This increased to approximately 13% at 75 mg/kg and 15% to 20% at 150 mg/kg. These findings suggest a strong, but saturable, first-pass metabolic effect, leading to a nonlinear relationship between dose and parent chemical dosimetry. No parent methyleugenol was found in urine from males dosed with methyleugenol orally or by intravenous injection. Hydroxylated, sulfated, and glucuronidated metabolites constituted the majority of metabolites detected in urine.

Metabolism (mice):
Approximately 85% of methyleugenol orally administered to females was eliminated in urine as parent or metabolites by 72 hours after dosing. Bioavailability of methyleugenol was low, with 3% to 5% bioavailability at 25 mg/kg. This increased to approximately 12% at 50 mg/kg and 13% to 19% at 75 mg/kg. These findings suggest a strong, but saturable, first-pass metabolic effect, leading to a nonlinear relationship between dose and parent chemical dosimetry. No unchanged methyleugenol was found in urine from females dosed with methyleugenol orally. Hydroxylated, sulfated, and glucuronidated metabolites constituted a minority of the metabolites detected in urine, with the majority unknown.
Conclusions:
Methyleugenol is rapidly absorbed following oral administration to rats and mice. The kinetic data are consistent with rapid clearance from the blood, metabolism in the liver, and excretion of the parent and various metabolites in the urine.

Description of key information


Methyleugenol is rapidly absorbed following oral administration to rats and mice. The kinetic data are consistent with rapid clearance from the blood, metabolism in the liver, and excretion of the parent and various metabolites in the urine.

Key value for chemical safety assessment

Bioaccumulation potential:
low bioaccumulation potential
Absorption rate - oral (%):
100

Additional information