Comparative beta-adrenoceptor blocking effects and pharmacokinetics of penbutolol and propranolol in man

1 The beta-adrenoceptor blocking effects of penbutolol were compared with those of propranolol and a placebo in a double-blind trial involving six healthy volunteers. 2 Heart rate (HR), systolic blood pressure (SBP) and peak expiratory flow rate (PEFR) were measured at rest and during vigorous exercise before and at intervals up to 7 h after oral administration of the drugs. In addition, plasma Renin activity (PRA) at rest and plasma levels of penbutolol and propranolol were determined. 3 Penbutolol proved to be a non-cardioselective beta-adrenoceptor blocking drug, antagonizing exercise-induced tachycardia, reducing exercise-induced increase in PEFR and decreasing PRA. The beta-adrenolytic potency of penbutolol was shown to be four-fold that of propranolol but the duration of its effect was similar. 4 The peak plasma level of penbutolol was reached 1 h after administration and its half-life was 4.5 h. 5 Comparison of plasma levels and biological activity of penbutolol revealed that after oral administration this drug is transformed into an active metabolite in man.