Abstract

The cytochrome P450 (P450) 2D subfamily catalyzes ring hydroxylation of amphetamines. We tested the hypothesis that P450 2D is selectively involved in amphetamine 4-hydroxylation. Urinary elimination of 4-hydroxyamphetamine and amphetamine was determined in male Sprague-Dawley rats pretreated with P450 inducers and inhibitors. The urinary 24-h metabolic ratio (amphetamine/4-hydroxyamphetamine) was not affected by the inducers 3-methylcholanthrene, isosafrole, phenobarbital, ethanol, pregnenolone-α-carbonitrile, and clofibrate. Isosafrole did, however, increase amphetamine elimination along with urine volume. Urinary elimination of 4-hydroxyamphetamine was significantly decreased by, and the metabolic ratio increased by, the inhibitors 1-aminobenzotriazole, CCl₄, quinidine, quinine, and primaquine. Diallyl sulfide and troleandomycin had no effect. In rat liver microsomes primaquine was shown to be an inhibitor of 2D activity. Urine 4-hydroxyamphetamine content correlated strongly (r² = 0.989) with microsomal P450 2D activity in parallel-treated rats. These studies also substantiate that 4-hydroxylation of amphetamine is selectively performed by the P450 2D subfamily in the rat.