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Metoprolol
Metoprolol is a 2nd-generation, β1-selective beta-blocker.
It primarily blocks cardiac β1 receptors with minimal β2 activity at usual doses.
Classification: • 2nd Generation (Cardioselective) • No intrinsic sympathomimetic activity (ISA)
Available Formulations
Metoprolol exists in TWO forms:
1. Metoprolol Tartrate (Immediate-release)
2. Metoprolol Succinate (Extended-release)
These are NOT interchangeable.
Mechanism of Action
Blocks β1 receptors:
• ↓ Heart rate • ↓ Contractility • ↓ AV nodal conduction • ↓ Renin release
Net Effects:
• ↓ Cardiac output • ↓ Blood pressure • ↓ Myocardial oxygen demand
Cardioselectivity is dose-dependent.
Indications
Hypertension
• Not first-line for uncomplicated HTN • Useful when CAD, arrhythmia, or HFrEF present
Coronary Artery Disease / Post-MI
• Reduces mortality post-MI • Decreases myocardial oxygen demand
Arrhythmias
Heart Failure (HFrEF)
ONLY: • ★ Metoprolol Succinate
has proven mortality benefit.
Metoprolol tartrate does NOT have established mortality data in HFrEF.
Tartrate vs Succinate
Metoprolol Tartrate: • Immediate-release • Usually dosed twice daily • Common in inpatient setting • Used for acute rate control
Metoprolol Succinate: • Extended-release • Once daily dosing • Mortality benefit in HFrEF • Preferred outpatient formulation
Exam Pearl: If question involves heart failure mortality → choose succinate.
Adverse Effects
• Bradycardia • AV block • Hypotension • Fatigue • Depression • Erectile dysfunction • Masked hypoglycemia
Less bronchospasm risk than nonselective agents.
Contraindications
• Severe bradycardia • High-grade AV block (without pacemaker) • Cardiogenic shock • Acute decompensated heart failure
Use caution in: • Asthma (though safer than nonselective agents) • Diabetes
Clinical Pearls
✔ Cardioselective (β1 selective) ✔ Succinate reduces mortality in HFrEF ✔ Tartrate used more for acute rate control ✔ Dose-dependent loss of selectivity ✔ Not first-line for uncomplicated hypertension
For other HF mortality agents see:
→ Carvedilol → Bisoprolol
Related:
→ Beta-Blockers Overview → Heart Failure Module → Dysrhythmias Module → Hypertension Module → Return to Cardiovascular Modules