Beta-2 adrenoceptor blocking activity of penbutolol and propranolol at very low doses.

The relative potency of penbutolol, a new beta adrenergic receptor blocking agent, was compared with propranolol by a four-point assay on healthy male subjects. A dose-response relationship to intravenous doses of propranolol in the microgram range was obtained during a steady state of infusion of epinephrine. Two subjects underwent the entire assay according to the Latin square design and four others each underwent one schedule of design on different days. The potency of penbutolol thus assessed was consistent with reported results. This study emphasizes the importance of intersubject variation and differential receptor sensitivity in individuals. The use of epinephrine as a beta receptor adrenergic agonist for evaluation of selective beta adrenergic receptor blocking activities is discussed.