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

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Abstract
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.