Cimetidine impairs the elimination of chlormethiazole.

Cimetidine impairs the systemic clearance of a number of low extraction drugs and this study examines its effect on the oral clearance of the high extraction drug, chlormethiazole. Cimetidine (1 g/day for 7 days) caused the clearance of chlormethiazole to fall to 69% of pretreatment values. It also prolonged the elimination half-life by 60%. The findings indicate that the metabolism of chlormethiazole is inhibited by cimetidine and the co-administration of these drugs may lead to excess sedation and respiratory depression.