Antihypertensive effect and tolerability of metoprolol during long-term treatment: a multicentre study

A comparison of 100 mg atenolol and 100 mg metoprolol once a day at rest and during exercise in hypertensives

The effects of once daily dosage of the two cardioselective beta-adrenoceptor blocking agents, atenolol and metoprolol, were studied in 26 patients with primary hypertension. The study was a randomized double-blind cross-over trial with placebo run-in and wash-out. Assessment of effect was performed about 1 and 25 hours after dosing. At rest, both atenolol and metoprolol lowered the blood pressure (BP) and heart rate (HR) compared to placebo. Atenolol induced a more effective BP reduction than metoprolol, especially 25 hours after drug intake. During exercise 1 hour after dosing both drugs reduced BP and HR to a similar extent, whereas 25 hours after dosing atenolol gave a more efficient BP and HR reduction than metoprolol. Our data show that both 100 mg atenolol and 100 mg metoprolol are effective antihypertensive beta-blockers at rest and during exercise, 1 hour after intake. Metoprolol was less effective than atenolol 25 hours after dosing probably due to its shorter plasma half-life, thus implying a twice daily regimen for metoprolol in standard preparation.

Obesity and beta-blockers: influence of body fat on their kinetics and cardiovascular effects

Beta-blockers are among the most widely used antihypertensive drugs. They differ from each other in regard to several factors such as: beta-agonist activity, beta 1-selectivity and solubility. Aim of this work was to evaluate the influence of obesity on the kinetics and the antihypertensive effect of two Beta-blockers with different solubility such as: the water-soluble, atenolol and the liposoluble, metoprolol. The study was carried out according to an open randomized cross-over design. Eight obese hypertensive patients, after a two week washout period, were randomly allocated to a four week treatment. After a two week intermediate washout period, each patient switched to the other treatment for an additional four week period. On the first and the last day of each treatment the subjects were hospitalized to collect blood samples for the assay of the two drugs and to measure cardiovascular parameters. Obesity does not exert any effect on the kinetics of the water-soluble beta-blocker, atenolol, while markedly interferes with that of the liposoluble, without any apparent influence on its anti-hypertensive effect. These findings extend to obese hypertensives the concept that the plasma concentrations of beta-blocking agents are not reliable predictors of their therapeutic effect.

Relation of cardiovascular response to the hypotensive effect of metoprolol

The influence of cardioselective beta blockade on systemic hemodynamics and cardiac performance was assessed in 17 essential hypertensive patients treated with metoprolol (50 to 100 mg twice daily) for 1 month. Eleven patients had a significant reduction of mean arterial pressure (less than 10 mm Hg); the other six patients did not show significant blood pressure change. There was no difference in response of heart rate or cardiac output between the two groups [-14 +/- 1.6 (SE) vs. -9.5 +/- 2.08 bpm, NS, and -0.55 +/- 0.39 vs. 0.80 +/- 0.35 L/min, NS, respectively]. Mean transit time was significantly prolonged in both groups (1.9 +/- 0.56 vs. 1 +/- 0.53 seconds, NS), and changes in ejection fraction in the two groups were not significant. The only significant difference between the two groups was in the response of total peripheral resistance (-1.4 +/- 3.04 vs. +10.2 +/- 3.77 U . m2, p less than 0.05). The reduction in heart rate correlated significantly with control heart rate (r = -0.71, p less than 0.001) and the decreased in cardiac output correlated significantly (r = -0.77, p less than 0.001) and the decrease in cardiac output correlated significantly (r = -0.77, p less than 0.001) with the initial cardiac output. The changes in mean arterial pressure did not correlate with changes in cardiac output (r = 0.116). On the other hand, there was a significant correlation of 0.68 (p less than 0.01) between the changes in mean arterial pressure and the changes in total peripheral resistance. Changes in plasma renin activity (PRA) were not significant in the nonresponders (1.8 +/- 0.9 to 0.6 +/- 0.2 ng/ml, NS), and the reduction of plasma renin activity was significant in the group of responders (5.5 +/- 2.4 to 1.7 +/- 0.8 ng/ml, p less than 0.05). However, there was no correlation between the changes of mean arterial pressure and either initial PRA or the change in PRA. As regards plasma catecholamines (measured in nine patients), there was a tendency to reduction in both responders and nonresponders (411 +/- 84 to 319 +/- 67 ng/L and 562 +/- 141 to 388 +/- 166, respectively); but changes did not reach statistical significance in both groups. It was concluded that metoprolol reduces cardiac output by slowing heart rate; this reduction of cardiac output was not related to decreased cardiac performance. The mechanism of blood pressure reduction seems to be related to the response of systemic resistance to the diminution in cardiac output and not to the decrease in cardiac output per se, inasmuch as the latter occurred in both responders and nonresponders.

Metoprolol overdose

We report the first two documented cases of the deliberate metoprolol overdose occurring in the United States, one of which eventually proved fatal. The potentially lethal cardiotoxic effects of this drug are illustrated and correlated with the blood and tissue levels of metoprolol. We emphasize the often sudden and rapid clinical deterioration which excessive ingestion of this drug may produce, and the need for close, careful supervision and monitoring of these patients.

Results from a multicentre trial of metoprolol and a study of hypertensive patients with chronic obstructive lung disease

Ninety-nine patients took part in a multicentre, long-term study of metoprolol in the treatment of hypertension. Significant reductions in blood pressure and heart rate were achieved by the use of metoprolol alone, or in combination with other antihypertensive agents. Side effects were similar to those seen with other beta-adrenergic blocking agents, except that bronchospasm and cold extremities were rarely encountered. Results of monitoring for the abnormal eye symptoms and antinuclear factor titre are discussed. In a second study, 14 hypertensive patients with asthma (11 patients) or history thereof (three patients), received metoprolol for their hypertension. In general, no significant change in forced expiratory volume in one second (FEV1) was found, despite significant reduction in blood pressure and heart rate. The concomitant use of a beta2-agonist is discussed.