II. Kinetics and metabolism of theobromine in male and female non-pregnant and pregnant rabbits

The kinetics and metabolism of theobromine (3,7-DMX) were investigated in male rabbits after a single oral dose and 14 days oral dosing at 1, 5, 10, 50 and 100 mg/kg/day. Female non-pregnant and pregnant rabbits were also studied after single oral doses of 1, 5 and 50 mg/kg. No significant difference was found in the pharmacokinetic profile of 3,7-DMX due to either sex, pregnancy or after chronic oral administration for 14 days. Intravenous (i.v.) administration of 3,7-DMX at 1 and 5 mg/kg resulted in calculated kinetic parameters in close agreement with oral doses. Irrespective of sex, there was a reduction in the absorption rate constant as the dose increased, coupled with a linear dose-related increase in AUC values. No qualitative difference in the metabolism of 3,7-DMX in the rabbit was observed as linked to sex, pregnancy or treatment schedule. Twenty-five percent of the administered dose of 3,7-DMX was excreted unchanged, the major metabolite being 7-methylxanthine (40%). There appeared to be a shift in the metabolic pathway at 100 mg/kg/day in the males and at 50 mg/kg/day in the females with more unchanged 3,7-DMX excreted. Only at these highest doses (100 mg/kg for males and 50 mg/kg for pregnant rabbits) was there a tendency toward accumulation.