Abrupt propranolol withdrawal and myocardial contractility. A study of effects in normal man.

Acute coronary artery syndromes, including unstable angina and myocardial infarction, have been desribed after the abrupt withdrawal of beta-adrenergic blocking agents. One possible mechanism is a hyperinotropic state resulting from a rebound hypersensitivity to endogenous catecholamines. Propranolol hydrochloride was administered to 21 healthy subjects for 15 days. Systolic time intervals and 24-hour urinary excretion of vanillylmandelic acid (VMA) were measured serially before, during, and after administration. Serial serum propranolol levels were measured during and after administration. Inhibition of exercise-induced tachycardia by propranolol was established before and during drug administration.