Duration of cardiac effects of timolol and propranolol

The duration of the cardiac effects of single intravenous doses of the beta-antagonists, timolol and propranolol, was compared in 6 healthy male subjects. Timolol and propranolol were given in doses of 1 mg and 10 mg, respectively, and at specified times after their administration, beta-blockade was assessed by the reduction of maximal exercise-induced tachycardia and by the inhibition of the chronotropic and inotropic effects of isoproterenol. Inotropic effects were measured by changes in the pre-ejection period of left ventricular systole obtained from systolic time intervals. There was no statistically significant difference in the timolol and propranolol time-courses of beta-blockade. The change in exercise-tachycardia was maximal 5 min after beta-antagonist infusion but dissipated rapidly so that no statistically significant change was observed 9 hr later. The chronotropic and inotropic effects of isoproterenol were almost completely antagonized for 11/2 hr after beta-antagonist infusion, and significant beta-blockade could be demonstrated 9 hr later. There was no difference in the time-course of the negative chronotropic and inotropic effects of either beta-antagonist.