The influence of cimetidine on debrisoquine 4-hydroxylation in extensive metabolizers.

We have studied the effect of cimetidine (800 mg.day-1) administration for three days on debrisoquine 4-hydroxylation in nine healthy extensive metabolizers. The debrisoquine metabolic ratio was significantly increased (p less than 0.01), but the new ratios remained in the extensive metabolizer range (less than 12.6). These data suggest that pre-treatment with cimetidine in usual therapeutic doses will impair debrisoquine 4-hydroxylation, but not enough to alter the apparent oxidation phenotype.