Influence of pentobarbital on metoprolol plasma levels

Induction of microsomal enzymes with barbiturates in rats has little effect on the metabolism of metoprolol, compared with propranolol and alprenolol, which undergo extensive hepatic extraction in animals and man. Our study was designed to examine whether the metabolism of metoprolol is inducable by barbiturate in man. In 8 healthy subjects the area under the plasma concentration/time curve after 0.1 gm metoprolol was reduced by a mean of 32% after treatment with 0.1 gm pentobarbital at bedtime for 10 days. There was considerable interindividual variability in the reduction after pentobarbital treatment (2% to 46%).