Pharmacokinetics of propranolol and its metabolites in horses after intravenous or oral administration

The pharmacokinetics characteristics of propranolol (PPL) in horses was stu died by administering the drug intravenously or orally to the animals, The predominant primary pathway was ring oxidation, and 4-hydroxypropranolol gl ucuronide (4-OHPG), was the major metabolite in both plasma and urine, Side -chain glucuronidstion and oxidation were not significant. A two-compartmen t model was employed for PPL followed by a one-compartment model for 4-OHPG . After oral administration, one-step absorption and two-step first pass me tabolism were employed. The fraction absorbed of PPL was approximately. 70% after. oral administration, and the bioavailability. varied among individu al horses from 1 to 79% depending on the first pass metabolism, The biologi c half-life (T-1/2) of PPL obeys the allometric equation in some animal spe cies including rats and horses, except for human, T-1/2 of PPL in horses wa s approximately 2 h.