Due to AstraZeneca’s marketing exclusivity rights, this generic drug product is not labeled for pediatric use. Pharmacokinetic information for pediatric patients 6 to 17 years of age is approved for AstraZeneca’s metoprolol succinate extended-release tablets.
The mechanism of the antihypertensive effects of beta-blocking agents has not been elucidated. However, several possible mechanisms have been proposed: (1) competitive antagonism of catecholamines at peripheral (especially cardiac) adrenergic neuron sites, leading to decreased cardiac output; (2) a central effect leading to reduced sympathetic outflow to the periphery; and (3) suppression of renin activity.
In a double-blind study, 1092 patients with mild-to-moderate hypertension were randomized to once daily metoprolol succinate extended-release tablets (25, 100, or 400 mg), felodipine extended-release tablets, the combination, or placebo. After 9 weeks, metoprolol succinate extended-release tablets alone decreased sitting blood pressure by 6-8/4-7 mmHg (placebo-corrected change from baseline) at 24 hours post-dose. The combination of metoprolol succinate extended-release tablets with felodipine extended-release tablets has greater effects on blood pressure.
In controlled clinical studies, an immediate-release dosage form of metoprolol was an effective antihypertensive agent when used alone or as concomitant therapy with thiazide-type diuretics at dosages of 100 to 450 mg daily. Metoprolol succinate extended-release tablets, in dosages of 100 to 400 mg once daily, produces similar beta1 -blockade as conventional metoprolol tablets administered two to four times daily. In addition, metoprolol succinate extended-release tablets administered at a dose of 50 mg once daily lowered blood pressure 24 hours post-dosing in placebo-controlled studies. In controlled, comparative, clinical studies, immediate-release metoprolol appeared comparable as an antihypertensive agent to propranolol, methyldopa, and thiazide-type diuretics, and affected both supine and standing blood pressure. Because of variable plasma levels attained with a given dose and lack of a consistent relationship of antihypertensive activity to drug plasma concentration, selection of proper dosage requires individual titration.
By blocking catecholamine-induced increases in heart rate, in velocity and extent of myocardial contraction, and in blood pressure, metoprolol reduces the oxygen requirements of the heart at any given level of effort, thus making it useful in the long- term management of angina pectoris.
In controlled clinical trials, an immediate-release formulation of metoprolol has been shown to be an effective antianginal agent, reducing the number of angina attacks and increasing exercise tolerance. The dosage used in these studies ranged from 100 to 400 mg daily. Metoprolol succinate extended-release tablets, in dosages of 100 to 400 mg once daily, has been shown to possess beta-blockade similar to conventional metoprolol tablets administered two to four times daily.
The precise mechanism for the beneficial effects of beta-blockers in heart failure has not been elucidated.
MERIT-HF was a double-blind, placebo-controlled study of metoprolol succinate extended-release tablets conducted in 14 countries including the U.S. It randomized 3991 patients (1990 to metoprolol succinate extended-release tablets) with ejection fraction ≤0.40 and NYHA Class II-IV heart failure attributable to ischemia, hypertension, or cardiomyopathy. The protocol excluded patients with contraindications to beta-blocker use, those expected to undergo heart surgery, and those within 28 days of myocardial infarction or unstable angina. The primary endpoints of the trial were (1) all-cause mortality plus all-cause hospitalization (time to first event) and (2) all-cause mortality. Patients were stabilized on optimal concomitant therapy for heart failure, including diuretics, ACE inhibitors, cardiac glycosides, and nitrates. At randomization, 41% of patients were NYHA Class II, 55% NYHA Class III; 65% of patients had heart failure attributed to ischemic heart disease; 44% had a history of hypertension; 25% had diabetes mellitus; 48% had a history of myocardial infarction. Among patients in the trial, 90% were on diuretics, 89% were on ACE inhibitors, 64% were on digitalis, 27% were on a lipid-lowering agent, 37% were on an oral anticoagulant, and the mean ejection fraction was 0.28. The mean duration of follow-up was one year. At the end of the study, the mean daily dose of metoprolol succinate extended-release tablets was 159 mg.
The trial was terminated early for a statistically significant reduction in all-cause mortality (34%, nominal p=0.00009). The risk of all-cause mortality plus all-cause hospitalization was reduced by 19% (p=0.00012). The trial also showed improvements in heart failure-related mortality and heart failure-related hospitalizations, and NYHA functional class.
The table below shows the principal results for the overall study population. The figure below illustrates principal results for a wide variety of subgroup comparisons, including U.S. vs. non-U.S. populations (the latter of which was not pre-specified). The combined endpoints of all-cause mortality plus all-cause hospitalization and of mortality plus heart failure hospitalization showed consistent effects in the overall study population and the subgroups, including women and the U.S. population. However, in the U.S. subgroup (n=1071) and women (n=898), overall mortality and cardiovascular mortality appeared less affected. Analyses of female and U.S. patients were carried out because they each represented about 25% of the overall population. Nonetheless, subgroup analyses can be difficult to interpret and it is not known whether these represent true differences or chance effects.
† Time to first event
‡ Comparison of treatment groups examines the number of hospitalizations (Wilcoxon test); relative risk and risk reduction are not applicable.
|Clinical Endpoint||Number of Patients||RelativeRisk(95% CI)||Risk ReductionwithMetoprolol Succinate Extended-release tablets||NominalP-value|
|Placebon=2001||Metoprolol Succinate Extended-release tabletsn=1990|
|All-cause mortality plus all-cause hospitalization†||767||641||0.81(0.73-0.90)||19%||0.00012|
|All-cause mortality plus heart failure hospitalization†||439||311||0.69(0.60-0.80)||31%||0.0000008|
|Death due to worsening heart failure||58||30||0.51(0.33-0.79)||49%||0.0023|
|Hospitalizations due to worsening heart failure‡||451||317||N/A||N/A||0.0000076|
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