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Drugs, Supplies and Delivery
Labetalol
Labetalol is a unique dual-action beta-blocker that also exhibits alpha-1 adrenergic blocking activity, making it effective in managing hypertension, particularly in emergencies like hypertensive crises. Its combined effects on heart rate and vascular resistance provide rapid blood pressure control with fewer reflex side effects. This article synthesizes evidence from the British National Formulary (BNF), Lippincott Textbook of Pharmacology, and Lange Basic & Clinical Pharmacology to detail its pharmacology, clinical applications, and safety profile.
Labetalol blocks beta-1, beta-2, and alpha-1 adrenergic receptors, leading to:
- Beta-1 Blockade: Reduces heart rate and myocardial contractility, lowering cardiac output.
- Alpha-1 Blockade: Causes peripheral vasodilation, decreasing systemic vascular resistance.
- Beta-2 Blockade: Mildly inhibits bronchial and vascular beta-2 receptors, though less pronounced than non-selective beta-blockers (Lippincott Textbook of Pharmacology).
This dual mechanism allows labetalol to lower blood pressure without significantly reducing heart rate or causing reflex tachycardia (Lange Basic & Clinical Pharmacology).
- Hypertensive Emergencies:
- Intravenous (IV) labetalol is used for rapid blood pressure control in conditions like hypertensive encephalopathy or aortic dissection (BNF).
- Chronic Hypertension:
- Oral labetalol is used for long-term management, particularly in pregnancy-induced hypertension.
- Off-Label:
- Perioperative hypertension, pheochromocytoma (with alpha-blockers).
- Hypertensive Emergencies (IV):
- Adults: 20 mg IV over 2 minutes, followed by 40–80 mg every 10 minutes (max 300 mg).
- Continuous infusion: 1–2 mg/min, titrated to response.
- Chronic Hypertension (Oral):
- Adults: 100 mg twice daily, increased to 200–400 mg twice daily (max 2.4 g/day).
- Pregnancy: Start at 100 mg twice daily, titrated as needed (BNF).
- Renal/Hepatic Impairment:
- Renal: No dose adjustment unless severe (eGFR <30 mL/min).
Hepatic: Reduce dose by 50% in cirrhosis
- Cardiovascular: Postural hypotension, bradycardia, flushing.
- CNS: Dizziness, fatigue, headache.
- Gastrointestinal: Nausea, vomiting.
Serious (Rare):
- Bronchospasm: Risk in asthma/COPD (less common than non-selective beta-blockers).
- Liver Dysfunction: Elevated liver enzymes (monitor LFTs).
- Heart Failure Exacerbation: Avoid in decompensated heart failure (Lange Basic & Clinical Pharmacology).
- Severe bradycardia, second-/third-degree heart block, cardiogenic shock.
- Asthma, severe hepatic impairment.
- Monitoring:
- Blood pressure, heart rate, and signs of fluid retention.
- Liver function tests (baseline and periodically).
- Pregnancy/Lactation:
- Pregnancy: Category C (safe in pregnancy-induced hypertension).
- Lactation: Excreted in breast milk; monitor infant for bradycardia (BNF).
- Calcium Channel Blockers (e.g., verapamil): Additive bradycardia and hypotension.
- Cimetidine: Increases labetalol levels (reduce dose).
- Insulin/Sulfonylureas: Masks hypoglycemia symptoms (e.g., tremor, tachycardia).
- Tricyclic Antidepressants: May antagonize antihypertensive effects (Lippincott Textbook of Pharmacology).
- Generic: Labetalol hydrochloride.
- Brand Names: Trandate® (UK), Normodyne® (US).
- Formulations: Tablets (100 mg, 200 mg, 400 mg), IV solution (5 mg/mL).
