Propranolol in the treatment of angina pectoris. Comparison of duration of action in acute and sustained oral therapy.

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Abstract
The duration of action of single oral doses of 80 and 160 mg of propranolol during acute and sustained therapy was studied in 9 patients with stable, exercise-induced angina pectoris. Plasma propranolol levels peaked 2 h after both doses during acute and sustained therapy, but there were wide variations between individuals in plasma concentration with both dosage schedules. Plasma half-lives after 80 and 160 mg were 3.99 and 4.65 h during acute therapy and 3.46 and 6.35 h during sustained therapy. Despite a 2-fold increase in plasma levels during sustained therapy, the increase in walking time to angina was similar to that seen with acute therapy. After acute administration of 80 and 160 mg propranolol, walking time to angina increased significantly compared with the values after placebo. This improvement in exercise tolerance was similar after the 2 doses of propranolol; it appeared within 1 h and persisted for 12 h after both doses. Improvement in exercise tolerance was maintained over 12 h during sustained therapy 2 .times. daily with 80 mg propranolol. When the dose of propranolol was increased to 160 mg 2 .times. daily, no further improvement in exercise tolerance was observed. During both modes of therapy, the improvement in exercise tolerance was associated with significant reduction in ECG ST-segment depression. At both rest and exercise, the heart rate, systolic blood pressure and rate-pressure product decreased at 1 h and the effects persisted for 12 h during acute therapy and for 24 h during sustained therapy. The circulatory effects were more marked during sustained therapy. Therapy 2 .times. daily with 80 mg propranolol should be adequate for treating patients with angina pectoris due to coronary artery disease. The improvement in exercise tolerance to be expected during sustained therapy can be assessed from the exercise studies carried out within 1-2 h after the oral administration of single dose of 80 or 160 mg propranolol.