Group II antiarrhythmics

Generic and Brand Names

• Propranolol — Inderal, Inderal LA

• Metoprolol — Lopressor, Toprol-XL

• Esmolol — Brevibloc

• Atenolol — Tenormin

• Nadolol — Corgard

• Bisoprolol — Zebeta

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Class

• Vaughan Williams Class II antiarrhythmics

• Beta-adrenergic receptor antagonists (beta-blockers)

• May be cardioselective (β1) or nonselective (β1 + β2)

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Mechanism of Action

• Block beta-adrenergic receptors, reducing sympathetic stimulation of the heart

• Primary cardiac effects:

  • Decrease SA node automaticity → slower heart rate

  • Slow AV node conduction → increased refractory period

  • Reduce myocardial contractility (negative inotropy)

• Reduce oxygen demand and suppress catecholamine-induced arrhythmias

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Indications

• Supraventricular arrhythmias (especially rate control in atrial fibrillation/flutter)

• Ventricular arrhythmias precipitated by catecholamines (e.g., post-MI)

• Prevention of sudden cardiac death in post-MI and heart failure patients

• Long QT syndrome (congenital) to reduce arrhythmia risk

• Rate control in inappropriate sinus tachycardia

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Dosage and Administration

Propranolol

• Oral: 10–40 mg 3–4 times daily or LA formulation 80–320 mg daily

• IV (acute arrhythmia): 1 mg over 1 min, may repeat q2min up to 5 mg

Metoprolol

• Oral: 25–100 mg 2–3 times daily (tartrate) or 50–200 mg once daily (succinate)

• IV: 2.5–5 mg q2–5min up to 15 mg total

Esmolol

• IV only: Bolus 500 mcg/kg over 1 min, then infusion 50–300 mcg/kg/min

• Ultra–short acting, ideal for acute perioperative arrhythmia control

Atenolol

• Oral: 25–100 mg once daily

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Monitoring

• Heart rate, blood pressure

• ECG (PR interval, QRS duration, rhythm)

• Signs of heart failure

• Blood glucose in diabetic patients (masking of hypoglycaemia)

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Contraindications

• Severe bradycardia

• 2nd- or 3rd-degree AV block without pacemaker

• Sick sinus syndrome without pacemaker

• Cardiogenic shock

• Uncompensated heart failure

• Severe asthma or COPD (nonselective beta-blockers)

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Precautions

• Use cardioselective agents in patients with mild-moderate reactive airway disease

• Taper gradually to avoid rebound tachycardia, hypertension, and arrhythmia

• Adjust dose in renal impairment for renally cleared agents (atenolol, nadolol)

• Use with caution in diabetes — masks hypoglycaemic symptoms

• Avoid abrupt discontinuation, especially in ischemic heart disease

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Adverse Effects

• Bradycardia, hypotension, fatigue, dizziness

• Worsening heart failure in susceptible patients

• Bronchospasm (nonselective agents)

• Depression, vivid dreams (lipophilic agents like propranolol)

• Sexual dysfunction, cold extremities

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Drug Interactions

• Calcium channel blockers (verapamil, diltiazem): Additive bradycardia, AV block, hypotension

• Other antihypertensives: Additive hypotensive effect

• Antiarrhythmics: Additive conduction suppression

• Insulin/oral hypoglycaemics: Masking of hypoglycaemia symptoms

• Clonidine: Rebound hypertension risk if clonidine withdrawn abruptly while on beta-blocker

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Overdose

• Manifestations: Severe bradycardia, hypotension, cardiogenic shock, bronchospasm, hypoglycaemia

• Management:

  • Atropine for bradycardia

  • IV fluids and vasopressors for hypotension

  • Glucagon (increases cAMP independent of beta-receptors)

  • High-dose insulin–glucose therapy for severe cardiogenic shock

  • Temporary pacing if required

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Patient Counselling

• Take medication consistently at the same time each day

• Do not stop suddenly without medical advice

• Monitor pulse — report if <50 bpm with symptoms

• In diabetes, monitor blood sugar closely — symptoms of low blood sugar may be masked

• Report signs of worsening breathing difficulty (nonselective agents)

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Comparison Table — Cardioselective vs Nonselective Beta-blockers

Feature	Cardioselective (β1) — e.g., Metoprolol, Atenolol, Bisoprolol	Nonselective (β1 + β2) — e.g., Propranolol, Nadolol
Primary Cardiac Effect	AV nodal slowing, reduced HR, ↓ contractility	Same, plus β2 blockade
Bronchospasm Risk	Lower (still possible at high doses)	Higher
Use in Asthma/COPD	Preferred (with caution)	Avoid
Lipid Solubility	Varies — metoprolol (moderate), atenolol (low)	Propranolol (high) — more CNS effects
Half-life	Atenolol, bisoprolol: long; metoprolol: intermediate	Nadolol: long; propranolol: intermediate
Extra Uses	Post-MI, heart failure, rate control	Migraine prophylaxis, essential tremor, thyrotoxicosis