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 cardioselective beta-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 fluorometrically 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 beta-adrenoceptor antagonist; its advantages as a cardioselective agent over practolol in therapeutic use are discussed.

Effects of cardioselective beta adrenoceptor blockade on specific airways resistance in normal subjects and in patients with bronchial asthma

“…The details of these methods have been presented elsewhere. 28 Samples for the measurement of plasma tolamolol concentration taken and deep-frozen for dispatch for analysis at Pfizer Research Laboratories were unfortunately lost in transit.…”

Plasma Catecholamines and Cardiovascular Responses to Hypoglycemia in Hyperthyroidism before and during Treatment with Metoprolol or Propranolol*

“…On the other hand, another explanation could be that the amounts of metoprolol and propranolol used are not equipotent in the degree of /?-adrenergic blockade. This interpretation seems less probable, since we used doses of the two /?-adrenergic antagonists which are considered equipotent in reducing exercise-induced tachycardia (31). Another factor which supports the equipotency of the doses used is the similar reduction of basal HRs in both treatment groups.…”

A Salute to Our Founding Editor-in-Chief Bramah N. Singh, MD, DPhil, DSc, FRCP

“…Although Dr Singh is well known for his major impact on defining the pharmacologic properties of antiarrhythmic agents, he has also published extensive works in the field of cardioprotection, [10][11][12][13][14][15] including studies on the effects of calcium channel blockers 14,15 and b blockers 11,13 on myocardial ischemia and myocardial infarction. Dr Singh has carried out numerous studies that have helped define the current pharmacologic therapy for angina pectoris and silent ischemia [16][17][18][19][20] -including studies on calcium blockers. 19 21 '' he described the revolution in synthesis and characterization of new pharmacologic agents that were made available in the second half of the 1900s, the advances being made in biotechnology using recombinant DNA techniques, and the birth of gene therapy.…”