THE EFFECTS OF PROPRANOLOL, PRACTOLOL AND METOPROLOL ON EXERCISE‐INDUCED TACHYCARDIA IN RELATION TO PLASMA LEVELS IN MAN

Abstract

1. The effects of single oral doses of propranolol, practolol and a new cardio‐selective β‐adrenoceptor blocking drug, metoprolol, on exercise‐induced tachycardia in relation to plasma levels were studied in six normal volunteers. 2. Exercise undertaken on treadmill was submaximal which, under control conditions, increased the heart rate from 74·3 (s.e.m. = 6·8) to 153·8 (s.e.m. = 9·8) beats/min. 3. Plasma concentrations of propranolol and practolol were assayed fluoro‐metrically and of metoprolol by electron‐capture gas liquid chromatography, the details of which are described. 4. Between 1·5 and 2 h after drug ingestion 80 mg of propranolol associated with plasma level of 50–60 ng/ml (half‐life 2·75 h), reduced the exercise‐induced tachycardia by 27%, 250 mg of practolol with plasma levels of 1050–1100 ng/ml reduced it by 28% and 100 mg of metoprolol with plasma concentrations of 140–150 ng/ml (half‐life 1·7 h), reduced it by 30%. 5. The resting heart rates were reduced significantly by propranolol and metoprolol but not by practolol. 6. Metoprolol is a potent short‐acting β‐adrenoceptor antagonist; its advantages as a cardioselective agent over practolol in therapeutic use are discussed. Copyright © 1976, Wiley Blackwell. All rights reserved