| Drug class |
Class IC anti‑arrhythmic (sodium‑channel blocker) |
Selective β₁‑adrenergic blocker (beta‑blocker) |
| Primary mechanism |
Rapidly blocks fast inward Na⁺ currents → slows conduction, prolongs action‑potential duration, and reduces excitability of atrial and ventricular tissue. |
Blocks β₁‑adrenergic receptors → ↓ heart rate, ↓ contractility, ↓ renin release, ↓ afterload. |
| Key indications |
• Paroxysmal supraventricular tachycardia (PSVT)
• Atrial fibrillation/flutter (rate‑controlled)
• Ventricular arrhythmias (rare, in selected patients) |
• Hypertension
• Stable angina
• Heart failure (NYHA II–IV, LVEF < 40 %)
• Post‑MI prophylaxis
• Atrial fibrillation/flutter (rate control) |
| Contraindications |
• Structural heart disease (ischemic, valvular, dilated)
• Heart failure (NYHA III–IV)
• Conduction system disease (AV block)
• Pregnancy (Category C) |
• Severe bradycardia (< 50 bpm)
• Second‑ or third‑degree AV block
• Severe heart failure (NYHA III–IV) without evidence of benefit
• Severe asthma or COPD (β₂ blockade)
• Pregnancy (Category C) |
| Common side effects |
• Torsades de pointes, other ventricular arrhythmias (proarrhythmia)
• QRS widening, QT prolongation
• Headache, dizziness, nausea
• Rare: visual disturbances, tremor |
• Bradycardia, fatigue, dizziness
• Hypotension
• Bronchospasm (esp. in asthmatics)
• Sexual dysfunction, sleep disturbances |
| Drug interactions |
• Other sodium‑channel blockers (amiodarone, lidocaine) → ↑ proarrhythmia
• CYP‑dependent metabolism: inhibitors (cimetidine, fluoxetine) ↑ levels
• Avoid simultaneous use with Class III anti‑arrhythmics (e.g., sotalol) |
• CYP2D6 inhibitors (paroxetine, fluoxetine) ↑ metoprolol levels, risk of bradycardia
• Calcium‑channel blockers (verapamil, diltiazem) → additive ↓ heart rate
• Digoxin, other AV‑node blockers ↑ risk of AV block |
| Monitoring |
• Baseline & follow‑up ECG for QRS duration and QTc
• Serum flecainide level if therapeutic drug monitoring is done
• Renal function (dose adjustment) |
• Baseline & periodic BP & HR
• ECG for conduction changes
• Renal & hepatic function for dose adjustment (especially in CKD) |
| Dose (oral) |
• 100 mg PO BID (start 50 mg PO BID if > 35 kg or renal impairment)
• Titrate gradually to target QRS < 110 ms |
• 50–100 mg PO BID (or 100 mg daily)
• Titrate to HR 60–80 bpm, BP 120/80 mmHg |
| Pharmacokinetics |
• Bioavailability ≈ 70–80 %
• Hepatic metabolism (CYP3A4, CYP2D6)
• Half‑life 20–30 h (steady‑state 3–5 days)
• 70 % renal excretion |
• Bioavailability 25–30 % (poor oral absorption)
• CYP2D6 metabolism
• Half‑life 3–4 h (steady‑state 10–12 h)
• 25 % renal, 75 % hepatic |