Comparison of cardiac effects of timolol and propranolol

The cardiac effects of the β‐adrenergic blocking agent, timolol, were compared to those of propranolol after intravenous administration in 6 healthy male subjects. The effects of timolol and propranolol on maximal exercise‐induced tachycardia were measured. Timolol was about ten times as potent as propranolol in antagonizing exercise‐induced tachycardia. Dose‐response curves to intravenous infusions of isoproterenol were obtained after three doses of each β‐antagonist. Changes in myocardial contractility were assessed by cardiac systolic time intervals and were compared to the simultaneous changes in heart rate elicited by isoproterenol. For the 6 subjects, the mean potency ratios of timolol to propranolol as an antagonist of the chronotropic and inotropic effects of isoproterenol were 13.8 (±0.8) and 12.7 (±1.0), respectively. Neither timolol nor propranolol acted more selectively on β‐receptors affecting heart rate than on those influencing contractility.

Comparison of cardiac effects of timolol and propranolol Journal Articles