[Extent of beta-blocking action of S- and R-penbutolol during exercise testing (author's transl)]

The effect of 40 mg penbutolol (pure S-form = laevo penbutolol) and 40 mg isopenbutolol (pure R-form) on heart rate and blood pressure during exercise testing was investigated under double-blind, randomized, placebo-controlled conditions in 9 probands. 1.5 and 5.5 hours after ingestion of 40 mg penbutolol, resting, standing, exercise, and recovery heart rate as well as systolic pressure during exercise displayed a significant decline. Diastolic blood pressure rose slightly 1.5 hours after penbutolol. Isopenbutolol had no significant effect on resting and standing heart rate. 1.5 hours after ingestion, a slight reduction in exercise and recovery heart rate could be confirmed. The decline, however, was significantly lower than that achieved with penbutolol. In comparison with its dextrorotatory isomer, isopenbutolol, penbutolol has an approximately 100-fold more potent effect on exercise heart rate. This is also reflected in the drug's duration of action.