Phenotypic consistency in hydroxylation of desmethylimipramine and debrisoquine in healthy subjects and in human liver microsomes

The 2‐hydroxylation of desmethylimipramine (DMI) and the 4‐hydroxylation of debrisoquine (D) were studied in healthy subjects and in human liver microsomes. A single oral dose of DMI (25 mg) was given to 18 healthy subjects previously phenotyped with D (13 rapid and five slow hydroxylators). Urine was collected for 24 hr and DMI and total 2‐hydroxydesmethylimipramine (2‐OH‐DMI) levels were determined by HPLC. The urinary ratio DMI/2‐OH‐DMI correlated strongly (r = 0.92) with the urinary ratio of D to 4‐hydroxydebrisoquine (D/4‐OH‐D). The two hydroxydations were also studied in human liver microsomes from 10 different subjects. Formation rates of the hydroxylated metabolites correlated strongly (r = 0.869). Moreover, D competitively inhibited the 2‐hydroxylation of DMI. These findings suggest that both are hydroxylated by the same cytochrome P‐450 isozyme. Clinical Pharmacology and Therapeutics (1984) 36, 677–682; doi: 10.1038/clpt.1984.239