Generic Name

Metoprolol

Mechanism

• β1‑selective blockade of adrenergic receptors in the heart → ↓heart rate (chronotropic effect) and ↓contractility (inotropic effect).
• ↓Sympathetic drive → ↓renal renin release → reduced angiotensin‑converting‑enzyme pathway activity.
• Attenuates myocardial oxygen demand and improves myocardial perfusion in ischemic states.

Pharmacokinetics

• Absorption: Oral bioavailability ≈ 50 % (oral) – 100 % IV.
• Onset: 30–60 min PO; IV onset ≈ 5 min.
• Half‑life: 3–6 h for the immediate‑release (IR) formulation; 12–14 h for the extended‑release (ER) formulation.
• Metabolism: Primarily hepatic via CYP2D6 → 2‑O‑xenile.
• Elimination: 80–90 % renal (≥ 70 % unchanged); remainder biliary.
• Drug interactions: CYP2D6 inhibitors (e.g., fluoxetine, paroxetine) increase plasma levels; β‑blocker antagonists (e.g., propranolol) enhance effects.
• Dosage adjustments: renal/hepatic impairment may prolong action but no formal dose change is required for mild to moderate impairment.

Indications

• Hypertension
• Angina pectoris (stable, unstable, and post‑MI prophylaxis)
• Acute myocardial infarction (first‑line β‑blocker therapy)
• Heart failure (reduced ejection fraction, HF‑REF) – improves survival.
• Cardiac arrhythmias: supraventricular tachycardia, ventricular tachycardia prophylaxis.
• Preventive cardiology: post‑PCI β‑blockade to reduce restenosis risk.

Contraindications

• Absolute: Severe bradycardia, second‑ or third‑degree AV block without pacemaker, cardiogenic shock, overt heart failure (EF < 30 % without evidence of benefit), severe asthma/COPD (β1 selectivity less protective).
• Relative: Systolic hypotension (< 90 mm Hg), hypoglycemia unawareness in diabetes, significant hepatic impairment (high‑dose use), skin manifestations of drug hypersensitivity.
• Warnings: May mask hypoglycemia symptoms; caution in patients with peripheral vascular disease; risk of precipitating heart failure in previously compensated patients.

Dosing

• Immediate‑Release (IR): 2–4 times daily.
• Extended‑Release (ER): Once daily, has 3–4 × lower peak plasma levels.
• IV: 5–10 mg bolus over 5 min → 5 mg/h infusion for 24 h; monitor BP, HR.

Adverse Effects

Common
• Bradycardia, dizziness, fatigue, fatigue‑related syncope.
• Hypotension, especially in volume‑depleted patients.
• Cold extremities, bronchoconstriction (rare allergic).
• GI upset: nausea, anorexia.

Serious
• Pulmonary‑related: bronchospasm, dyspnea (particularly in asthmatics).
• Severe bradyarrhythmias or AV block.
• Heart failure exacerbation.
• Hypoglycemia masking in diabetics; consider glucose monitoring.
• Peripheral edema (rare).

Monitoring

• Vital signs: HR and BP at each visit; particularly after dose changes or new drug interactions.
• Laboratory: Basic metabolic panel, electrolytes (esp. K⁺, Mg²⁺), liver function tests if prolonged use.
• Cardiac evaluation: ECG to assess QTc, HR range; ejection fraction if HF indication.
• Blood glucose if diabetic.
• Renal function if dosing in severe CKD.

Clinical Pearls

• IR vs. ER: ER formulations achieve flatter plasma curves; use in chronic stable disease to reduce HR fluctuations; IR preferable in acute settings (post‑MI, SCC).
• Metoprolol Tartrate vs. Succinate: Tartrate has faster onset (~30 min) vs succinate (~1 hr); designations matter when titrating post‑MI or tachycardia.
• Stop‑Start Strategy: Abrupt cessation can precipitate rebound tachycardia; taper 5–7 days prior to discontinuation.
• Poly‑specific β‑blockers: Carvedilol, atenolol – choose based on comorbid asthma (carvedilol protective) or need for metabolic considerations (atenolol renally eliminated).
• CYP2D6 polymorphism: Poor metabolizers may experience higher plasma concentrations; monitor for bradycardia or hypotension.
• Combination therapy: Metoprolol + ACE inhibitor/ARB yields additive mortality benefit in HF‑REF; target heart rate 55–60 bpm.
• Education: Inform patients about reporting dizziness or orthostatic hypotension; encourage routine BP checks.
• Dose adjustment in pregnancy: Category C; use for severe hypertension or MI but monitor maternal/fetal status.

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• This drug card encapsulates the essential pharmacologic profile and clinical applications of Metoprolol, designed for quick reference by medical students and practicing clinicians alike.