Metoprolol types
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Types and Effects of Metoprolol: A Comprehensive Overview
Introduction to Metoprolol
Metoprolol is a beta1-selective adrenergic receptor blocker widely used in the management of various cardiovascular conditions, including hypertension, angina pectoris, and chronic heart failure. It is available in different formulations, primarily immediate-release (IR) and controlled-release/extended-release (CR/XL) forms, each with distinct pharmacokinetic properties and clinical applications.
Immediate-Release Metoprolol
Pharmacokinetics and Metabolism
Immediate-release metoprolol is rapidly absorbed and metabolized primarily by the cytochrome P450 2D6 (CYP2D6) enzyme. Genetic polymorphisms in CYP2D6 significantly affect the drug's pharmacokinetics. Poor metabolizers (PM) exhibit higher plasma concentrations and prolonged half-life of metoprolol compared to extensive metabolizers (EM) and ultrarapid metabolizers (UM)2 5. This variability can lead to differences in clinical response and adverse effects, such as a higher risk of bradycardia in PMs2.
Clinical Applications
Immediate-release metoprolol is often used in acute settings, such as after myocardial infarction (MI). Studies have shown that metoprolol reduces the incidence of nonfatal reinfarction and sudden death in post-MI patients1 6. Additionally, it has been observed to decrease the need for pain-relieving treatments and the incidence of supraventricular tachyarrhythmias in these patients6.
Controlled-Release/Extended-Release Metoprolol (CR/XL)
Benefits in Chronic Heart Failure
Metoprolol CR/XL has been extensively studied in patients with chronic heart failure. The MERIT-HF trial demonstrated that metoprolol CR/XL significantly reduces all-cause mortality, sudden death, and deaths due to progressive heart failure in patients with NYHA class II-IV heart failure3 9. The drug improves left ventricular function and reduces neurohumoral activation, contributing to better clinical outcomes7 9.
Hemodynamic and Energetic Improvements
In patients with nonischemic dilated cardiomyopathy, metoprolol CR/XL has been shown to improve myocardial performance and efficiency without increasing myocardial oxygen consumption. This suggests enhanced myocardial energetics and a shift towards more efficient substrate utilization10.
Metoprolol in Special Populations
COPD Patients
The use of metoprolol in patients with chronic obstructive pulmonary disease (COPD) has been controversial. A randomized trial found no significant difference in the time to first COPD exacerbation between metoprolol and placebo groups. However, metoprolol was associated with a higher risk of exacerbations leading to hospitalization, raising concerns about its safety in this population4.
CNS-Related Symptoms
Metoprolol and atenolol, another beta1-adrenoceptor antagonist, have been compared for their effects on CNS-related subjective symptoms. Both drugs were found to negatively affect vitality and contentment shortly after administration, but these effects diminished over time. Metoprolol had a milder impact on sleep compared to atenolol8.
Conclusion
Metoprolol, available in immediate-release and controlled-release/extended-release formulations, plays a crucial role in managing various cardiovascular conditions. Its pharmacokinetics are significantly influenced by CYP2D6 genetic polymorphisms, affecting clinical outcomes and adverse effects. While metoprolol CR/XL has proven benefits in chronic heart failure, its use in COPD patients requires caution due to potential risks. Understanding the different types and effects of metoprolol can help optimize its therapeutic use and improve patient outcomes.
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Most relevant research papers on this topic
Long-term treatment with metoprolol after myocardial infarction: effect on 3 year mortality and morbidity.
Metoprolol treatment after myocardial infarction significantly reduces nonfatal reinfarction and sudden death in all patients, and cardiac death in those with a large infarct.
RCT
Large Human Trial
Highly CitedCYP2D6 polymorphism and its impact on the clinical response to metoprolol: A systematic review and meta-analysis.
CYP2D6 poor metabolizers may experience greater heart rate reduction and higher risk of bradycardia during metoprolol treatment compared to active CYP2D6 phenotypes.
Meta-Analysis
Very Rigorous JournalEffect of metoprolol CR/XL in chronic heart failure: Metoprolol CR/XL Randomised Intervention Trial in-Congestive Heart Failure (MERIT-HF)
Metoprolol CR/XL once daily in addition to standard therapy improved survival in chronic heart failure patients with decreased ejection fraction and symptoms, and was well-tolerated.
RCTLarge Human TrialHighly CitedMetoprolol for the Prevention of Acute Exacerbations of COPD.
Metoprolol treatment for moderate or severe COPD patients without established indications showed similar time to first exacerbation but more hospitalization for exacerbation.
RCTLarge Human Trial
Rigorous JournalHighly CitedMETA-ANALYSIS OF CYP2D6 METABOLIZER PHENOTYPE AND METOPROLOL PHARMACOKINETICS
CYP2D6 metabolizer phenotype significantly influences metoprolol pharmacokinetics and enantiomer-specific metabolism, with ultrarapid and extensive metabolizers showing greater R metabolism than poor metabolizers.
Meta-AnalysisRigorous JournalHighly CitedMetoprolol in acute myocardial infarction (MIAMI). A randomised placebo-controlled international trial. The MIAMI Trial Research Group.
Metoprolol may reduce mortality in high-risk acute myocardial infarction patients, but its effect on overall mortality and morbidity remains unclear.
RCTLarge Human TrialHighly CitedEffects of metoprolol CR in patients with ischemic and dilated cardiomyopathy : the randomized evaluation of strategies for left ventricular dysfunction pilot study.
Metoprolol CR improves left ventricular function, reduces renin-angiotensin system activation, and leads to fewer deaths in patients with symptomatic congestive heart failure.
RCTLarge Human TrialHighly CitedCNS-related subjective symptoms during treatment with beta 1-adrenoceptor antagonists (atenolol, metoprolol): two double-blind placebo controlled studies.
Both metoprolol and atenolol cause mild subjective symptoms, with atenolol showing a significant adverse effect on sleep, but no significant differences in Type A behavior.
RCTMetoprolol
Metoprolol CR/XL effectively decreases mortality and improves clinical status in patients with stable mild to moderate chronic heart failure due to left ventricular systolic dysfunction, and is effective in patients with ischaemic or dilated cardiomyopathy.
RCTEffect of metoprolol on myocardial function and energetics in patients with nonischemic dilated cardiomyopathy: a randomized, double-blind, placebo-controlled study.
Metoprolol treatment improves myocardial performance and energetics, and favorably alters substrate utilization in patients with nonischemic dilated cardiomyopathy.
RCTHighly Cited