The effect of cimetidine on the relative cardioselectivity of atenolol and metoprolol in asthmatic patients.

The effects of chronic cimetidine therapy on the pharmacodynamic properties of atenolol and metoprolol were assessed in eight asthmatic patients using a placebo-controlled trial. When atenolol and metoprolol were administered at doses which achieved an equivalent degree of beta1-adrenoceptor blockade, metoprolol caused a significantly greater reduction in mean forced expiratory volume in one second (FEV1). This demonstrates the greater cardioselectivity of atenolol. The reductions in mean FEV1 induced by either atenolol or metoprolol were each unaffected by cimetidine. Plasma levels of each of the beta-adrenoceptor blockers were not affected by the addition of cimetidine. The FEV1 in one patient was further reduced when cimetidine was administered with metoprolol, although there was no corresponding change in plasma levels of drug. In this patient there was no such further reduction in FEV1 with atenolol. This study has not provided evidence for a pharmacodynamic interaction between cimetidine and either atenolol or metoprolol, but further studies are indicated.