Propranolol in angina pectoris: duration of improved exercise tolerance and circulatory effects after acute oral...

The duration of the effects of single oral doses of 80 and 160 mg of propranolol was studied in 11 patients with stable, exercise-induced angina pectoris. After administration of both doses, plasma propranolol levels peaked at 2 hours in 8 of the 11 patients and thereafter declined exponentially with an average plasma half-life of 3.98 hours (range 1.4 to 4.3) after the 80 mg dose and 4.28 hours (range 1.9 to 5.4) after the 160 mg dose. There was wide interindividual variation in plasma propranolol concentration at any given time after each dose. Treadmill walking time to the onset of angina, the total duration of exercise and the total external work performed were significantly greater by 1 hour after each dose of propranolol than after placebo. This improvement in exercise tolerance persisted unchanged for 8 hours (P less than 0.001) and was still significant although less marked at 12 hours (P less than 0.05). Improvement in exercise tolerance after propranolol was associated with a significant reduction in S-T segment depression during exercise. Both at rest and during exercise, heart rate, systolic blood pressure and rate-pressure product decreased after propranolol, and these circulatory effects persisted for 12 hours. Changes in walking time, heart rate and systolic blood pressure were similar after 80 and 160 mg of propranolol. Despite the increase in exercise duration and in total work performed after propranolol, the rate-pressure product at the onset of angina was lower after propranolol. In view of the prolonged effects of single oral doses of 80 and 160 mg of propranolol, it is suggested that administration of propranolol twice daily should be adequate in treating patients with stable angina pectoris. These studies also demonstrate that routine measurement of plasma propranolol levels is of little practical value in the management of patients with angina pectoris.