What does Metoprolol (beta-blocker) do?

What Does Metoprolol Do?

Metoprolol is a beta-1 selective adrenergic receptor blocker (beta-blocker) that reduces heart rate, blood pressure, and myocardial contractility, making it effective for treating hypertension, angina, heart failure, and post-myocardial infarction patients. 1

Mechanism of Action

Metoprolol works through:

• Beta-1 selectivity: Primarily blocks beta-1 adrenergic receptors located in the myocardium 2, 1
• Cardiovascular effects:
  • Reduces heart rate at rest and during exercise
  • Decreases myocardial contractility
  • Reduces systolic blood pressure
  • Slows AV nodal conduction velocity
  • Decreases cardiac output 1

This cardioselectivity means metoprolol has less effect on beta-2 receptors (found in bronchial and vascular smooth muscle) compared to non-selective beta-blockers, though this selectivity is not absolute at higher doses 1.

Clinical Applications

1. Hypertension

Metoprolol reduces blood pressure through:

• Competitive antagonism of catecholamines at cardiac sites
• Decreased cardiac output
• Possible central effects reducing sympathetic outflow
• Suppression of renin activity 1

2. Angina Pectoris

Metoprolol helps manage angina by:

• Blocking catecholamine-induced increases in heart rate
• Reducing myocardial contractility
• Lowering blood pressure
• Decreasing oxygen requirements of the heart at any given level of effort 1, 2

3. Heart Failure

In heart failure patients, metoprolol CR/XL:

• Reduces mortality by approximately 34% 2, 3
• Decreases sudden death and death due to progressive heart failure
• Improves NYHA functional class and exercise capacity 3

4. Post-Myocardial Infarction

Metoprolol reduces mortality when administered after myocardial infarction 2.

Dosing Information

Typical dosing for angina:

• 50 to 200 mg twice daily 2

For heart failure:

• Starting dose: 12.5-25 mg once daily
• Target dose: Up to 200 mg once daily (gradually uptitrated) 2, 3

Important Clinical Considerations

Advantages of Metoprolol

• Beta-1 selectivity: May be safer in patients with asthma or COPD compared to non-selective beta-blockers, though caution is still needed 2
• Formulations: Available in immediate-release and controlled-release/extended-release (CR/XL) forms 3

Contraindications and Cautions

• Avoid in:

  • Marked first-degree AV block (PR interval >0.24s)
  • Second or third-degree AV block without pacemaker
  • Severe left ventricular dysfunction or heart failure (initially)
  • Patients at high risk for cardiogenic shock 2
  • Significant hypotension (systolic BP <90 mmHg)
  • Significant bradycardia (heart rate <50 bpm) 2

• Use with caution in:

  • Patients with asthma or COPD (start with low doses of beta-1 selective agent) 2
  • Diabetics (may mask hypoglycemia symptoms)

Common Side Effects

• Fatigue
• Dizziness
• Bradycardia
• Cold extremities 2

Monitoring During Treatment

• Heart rate and blood pressure
• ECG monitoring (especially during IV administration)
• Signs of bronchospasm in susceptible patients
• Signs of worsening heart failure 2

When initiating metoprolol in heart failure patients, start with a low dose and gradually increase at 1-2 week intervals to minimize side effects and optimize tolerability 3.

Metoprolol's effectiveness in reducing mortality and cardiovascular events has been demonstrated in multiple large clinical trials, making it a cornerstone therapy for several cardiovascular conditions 2, 3.