Effects of alpha- and beta-receptor blockade on systolic time intervals

Differential cardiovascular effects of propranolol, atenolol, and pindolol measured by impedance cardiography

We have evaluated Sramek's method of impedance cardiography as a non-invasive way of detecting the cardiovascular effects of drugs. We made cardiovascular measurements using the method during passive tilting and exercise 2 h after the oral administration of atenolol (50 and 100 mg), propranolol (40 and 80 mg), pindolol (5 and 10 mg), and placebo in seven separate studies involving eight healthy male volunteers. Equivalent doses of the pure antagonists atenolol (beta 1) and propranolol (beta 1, beta 2) produced similar reductions in heart rate, systolic blood pressure, and cardiac index, and increases in stroke volume and total peripheral resistance, particularly during exercise. In contrast the partial agonist pindolol produced increases in heart rate and cardiac index, and reductions in peripheral resistance at rest. During passive tilting and exercise pindolol reduced heart rate, but cardiac output and total peripheral resistance were unchanged except at the highest levels of exercise. The similar cardiovascular effects of atenolol and propranolol, but differing effects of pindolol, are consistent with reports using other methods of measurement. This suggests that impedance cardiography may have a place in the non-invasive assessment of the cardiovascular effects of drugs.

Systolic time intervals: a review of the method in the non-invasive investigation of cardiac function in health, disease and clinical pharmacology

Measurement of systolic time intervals is a valuable, non-invasive procedure to assess left ventricular performance, particularly when influenced by drugs. In this review, we discuss various factors affecting systolic time intervals, the therapeutic implications of the technique and its place among other non-invasive tests of cardiac function.

Cardiac effects of tricyclic antidepressant medication. A preliminary study of nortriptyline

Systolic time intervals and drug plasma concentrations have been measured in a group of patients receiving repeated treatment with nortriptyline. Significant positive correlations between plasma nortriptyline levels and prolongation of pre-ejection phase (P less than 0.005)) and increase in the ratio pre-ejection phase, left ventricular ejection time (P less than 0.05) were obtained. A deterioration in cardiac function, with increase in heart rate, resulting in a negative inotropic effect has been shown to occur with therapeutic doses of nortriptyline. The potential dangers of tricyclic antidepressant drugs on the heart in patients whose myocardium is already compromised or those who accumulate high plasma concentrations are emphasised.

Estimation of the plasma concentration and course of action of phentolamine based on its inhibitory effect on adrenaline-induced platelet aggregation

1 Orally administered phentolamine retards the first phase of adrenaline-induced platelet aggregation. The extent to which aggregation was inhibited was compared in blood samples from six healthy volunteers treated with phentolamine and samples to which various concentrations of the drug were added in vitro.

2 These experiments permitted conclusions to be drawn concerning the magnitude and time-course of the plasma concentrations reached after the administration of phentolamine. A dose of 40 mg of the standard formulation (SF) produced a maximum effect after 30 min corresponding to that of a phentolamine concentration of approximately 12 × 10^-8 M (≈34 ng/ml). After 3 h about one-third of the maximum effect persisted, and after 6 h only a slight degree of activity was still detectable. The slow-release formulation (SR) (100 and 200 mg) had a rapid onset of action (1 h); the maximum effect was observed after 4 h, corresponding to an estimated plasma concentration of phentolamine of 11 and 42 ng/ml respectively, and the duration of action was well in excess of 12 h.

3 The time-course of the increase in heart rate and the increase in myocardial contractility (as determined from the pre-ejection period) was largely consistent with the calculated time-course of the plasma concentrations: A dose of 40 mg SF produced its maximum effect after 30-60 min and had a duration of action of 3 h. The maximum effect of the SR formulation was reached after 4 h, and the duration of action was more than 10 h.

Hydrallazine or phentolamine as adjuncts to beta-adrenoceptor blockade/thiazide therapy in hypertension

Ten patients not maximally controlled on an oxprenolo/cyclopenthiazide regimen for moderately severe hypertension were treated in a double blind crossover trial with either hydrallazine (75-150 mg/day) or phentolamine (60-120 mg/day) or placebo in addition to their other therapy. Additional phentolamine therapy did not lower blood pressure significantly when compared with placebo. Additional hydrallazine (75-150 mg/day) produced an approximate 10 mm, Hg fall in diastolic blood pressure, but no significant fall in systolic blood pressure. Pulse rates did not alter with the addition of hydrallazine or phentolamine. In patients who fail to attain optimal blood pressure response to beta-adrenoceptor blocking drugs it is suggested that the addition of hydrallazine is a useful measure.

Probenecid and rifampicin serum levels

Serum-levels of rifampicin were investigated in patients receiving rifampicin alone or with other antituberculosis drugs. 2 g of probenecid given 30 min before 300 mg of rifampicin did not result in raising serum levels to more than half those achieved with the standard 600 mg dose of rifampicin. Hence probenecid should not be used to reduce rifampicin dosage in antituberculosis therapy.

Relation between plasma concentrations and cardiovascular effects of oral oxprenolol in man

Oxprenolol, 40, 80 and 160 mg, was administered orally to seven healthy volunteers. Over the following eight hours repeated measurements were made of the plasma concentrations and effects on heart rate, myocardial contractility (PEPc) and systolic and diastolic blood pressure in recumbency, in the upright position and during physical effort at a work load of 120 watts on a bicycle ergometer. The maximum plasma levels and the area beneath the plasma concentration curves increased roughly in proportion to the dosage increment. No evidence of first-pass inactivation in the liver was found. The half-life of the drug in plasma was approximately 80 minutes, irrespective of the dose administered. Oxprenolol slowed heart rate, prolonged PEPc and lowered systolic blood pressure, by comparison with values recorded after a placebo. The effects were generally least marked in the recumbent position and most marked during effort, when a clear-cut dose-response relation was found. The pharmacodynamic effects of oxprenolol were compared with its concentration in plasma. Marked beta-receptor blockade still persisted eight hours after dosing, although at this time, after doses of 40 and 80 mg, the drug could not be detected in plasma.