Biliary excretion of amphetamine and methamphetamine in the rat.

1. (14)C-labelled amphetamine and methamphetamine were injected into rats cannulated at the bile duct under thiopentone anaesthesia and the output of their metabolites in urine and bile was determined. 2. With amphetamine, 69% of the (14)C was excreted in the urine and 16% in the bile in 24h. The main metabolite in bile was the glucuronide of 4-hydroxyamphetamine. The output of unchanged amphetamine was much greater in cannulated rats than in intact rats. 3. With methamphetamine, 54% of the (14)C appeared in the urine and 18% in the bile. The main metabolite in the bile was the glucuronide of 4-hydroxynorephedrine. The output of amphetamine, a metabolite of methamphetamine, was much greater in cannulated rats than in intact rats. 4. Evidence has been obtained for the enterohepatic circulation of certain amphetamine and methamphetamine metabolites in the rat. 5. Thiopentone anaesthesia appeared to inhibit the ring hydroxylation of amphetamine administered as such or formed as a metabolite of methamphetamine.