Metoprolol

Overview

Selective beta-1 adrenergic receptor blocker. Reduces heart rate, myocardial contractility, and cardiac output, lowering blood pressure and myocardial oxygen demand.

Indications

Hypertension
Angina pectoris
Heart failure (succinate form)
Acute myocardial infarction
Atrial fibrillation/flutter rate control
Migraine prophylaxis

Contraindications

Sinus bradycardia (<45 bpm)
Heart block greater than first degree
Cardiogenic shock
Decompensated heart failure
Sick sinus syndrome without pacemaker

Classification

Cardiovascular Agents Beta Blockers Cardiovascular System

Mechanism of Action

Selective beta-1 adrenergic receptor blocker. Reduces heart rate, myocardial contractility, and cardiac output, lowering blood pressure and myocardial oxygen demand.

Pharmacodynamics

Cardioselective beta-blocker at therapeutic doses. Reduces resting and exercise heart rate. Decreases renin secretion.

Pharmacokinetics

Absorption: Rapid and complete oral absorption. Significant first-pass metabolism.
Distribution: Widely distributed. Crosses blood-brain barrier and placenta.
Metabolism: Extensive hepatic via CYP2D6. Polymorphic metabolism (poor vs extensive metabolizers).
Excretion: Renal (95% as metabolites, <5% unchanged).
Half-life: 3-7 hours (tartrate); 12-20 hours (succinate ER)
Bioavailability: 40-50%
Protein Binding: 12%

Dosage

Typical dosage: IR: 25-100mg twice daily. ER: 25-200mg once daily.

Available Forms

Tablet (immediate release)
Tablet (extended release)
IV injection

Side Effects

Common

Fatigue
Dizziness
Bradycardia
Hypotension
Depression

Serious

Severe bradycardia
Heart failure exacerbation
Bronchospasm

Rare

Psoriasiform rash
Raynaud phenomenon
Retroperitoneal fibrosis

Drug Interactions

major

Combined use may cause severe bradycardia, heart block, and hypotension. Avoid concurrent IV administration.

moderate

Discontinuation of clonidine while on beta-blocker may cause rebound hypertension. Discontinue beta-blocker several days before tapering clonidine.

Warnings

⚠️BLACK BOX WARNING

Do not abruptly discontinue. Gradually reduce dose over 1-2 weeks to avoid exacerbation of angina, myocardial infarction, and ventricular arrhythmias.

Pregnancy

Category C

Toxicity

LD50 ~2-3 g/kg (oral, rat)

Overdose

Symptoms: severe bradycardia, hypotension, bronchospasm, heart failure, cardiogenic shock. Treatment: atropine, glucagon, vasopressors, temporary pacing.

References

PMC3821578

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