labetalol
alpha/beta adrenoceptor antagonist· Brands: Trandate, NormodyneIVPO
Mechanism of action
Labetalol is a competitive antagonist at both alpha-1 and beta-1/beta-2 adrenergic receptors. Blockade of alpha-1 receptors causes vasodilation and reduces peripheral vascular resistance, while beta-blockade reduces heart rate and cardiac output. The combined action lowers blood pressure without the reflex tachycardia seen with pure alpha-blockers.
Pharmacokinetics
Labetalol is well absorbed orally but undergoes significant first-pass metabolism, resulting in a bioavailability of approximately 25%. It is metabolized in the liver, primarily by glucuronidation, and has a plasma half-life of about 6 to 8 hours. The drug is eliminated mainly in the urine and faeces, with less than 5% excreted unchanged.
Indications & dosing
Hypertension (oral)
Initial dose 100 mg twice daily; titrate to response. Usual maintenance 200-400 mg twice daily.
- adult · PO: 100–400 mg twice daily · Initial dose 100 mg twice daily; titrate to response. Usual maintenance 200-400 mg twice daily.
Hypertensive emergency (IV bolus)
Give initial 20 mg over 2 min; repeat 40-80 mg every 10 min as needed. Cumulative maximum 300 mg.
- adult · IV: 20–80 mg every 10 min PRN · Give initial 20 mg over 2 min; repeat 40-80 mg every 10 min as needed. Cumulative maximum 300 mg.
Hypertensive emergency (IV infusion)
Alternatively, infuse at 0.5-2 mg/min, titrating to blood pressure. Total dose should be limited.
- adult · IV: 0.5–2 mg/min continuous infusion · Alternatively, infuse at 0.5-2 mg/min, titrating to blood pressure. Total dose should be limited.
Hypertension in pregnancy (oral)
Used for severe hypertension in pregnancy. Titrate to response; maximum 2400 mg/day.
- adult · PO: 100–400 mg twice daily · Used for severe hypertension in pregnancy. Titrate to response; maximum 2400 mg/day.
Contraindications & precautions
- Bronchial asthma or history of bronchospasm · Can precipitate acute bronchoconstriction, even though labetalol has some alpha-blocking vasodilator activity.
- Second- or third-degree atrioventricular block · Without a pacemaker, may cause severe bradycardia or cardiac arrest.
- Cardiogenic shock · Labetalol reduces cardiac output and can worsen shock.
- Severe bradycardia · Risk of symptomatic bradycardia and conduction disturbances.
- Decompensated heart failure · Negative inotropic effect may worsen heart failure.
- Do not discontinue labetalol abruptly; taper the dose to avoid rebound hypertension or tachycardia.
- Monitor blood pressure and heart rate regularly, especially after initiating therapy or changing dose.
- Use with caution in diabetes mellitus; labetalol may mask hypoglycaemia symptoms such as tachycardia.
- Use with caution in patients with peripheral vascular disease (e.g., Raynaud's phenomenon) as beta-blockade may worsen symptoms.
- Monitor liver function tests, as labetalol can rarely cause hepatotoxicity; discontinue if liver injury is suspected.
- Use with caution in patients with hepatic impairment, as labetalol is predominantly metabolised in the liver; dose adjustment may be needed.
Adverse effects
- Dizziness
- Headache
- Fatigue
- Postural hypotensionserious
- Scalp tingling
- Nausea
- Bronchospasmserious
- Bradycardiaserious
- Heart blockserious
- Hepatotoxicityserious
Renal & hepatic adjustment
- eGFR 0+: No dose adjustment usually necessary.
- Hepatic impairment (mild): No dosage adjustment usually necessary; monitor for adverse effects.
- Hepatic impairment (moderate): Reduce initial dose and titrate slowly; monitor hepatic function.
- Hepatic impairment (severe): Avoid use; labetalol is contraindicated in severe hepatic impairment. (avoid)
Monitoring, pregnancy & toxicity
- Blood pressure · Before starting, during titration, and regularly during maintenance.
- Heart rate · Before starting and during titration.
- Liver function tests · Baseline and periodically during treatment.
- Signs of bronchospasm · At baseline and if patient reports respiratory symptoms.
- Blood glucose · In diabetic patients, regularly.
- Pregnancy: Labetalol is a preferred agent for treating hypertension in pregnancy, including pre-eclampsia. It is generally considered safe and effective.
- Toxicity: Bradycardia · Supportive management; if symptomatic, give IV atropine. For refractory bradycardia, consider glucagon.
- Toxicity: Hypotension · IV fluids and vasopressors as needed. Monitor blood pressure closely.
- Toxicity: Bronchospasm · Administer inhaled beta-2 agonists (e.g., salbutamol). Consider intravenous aminophylline if severe.
- Toxicity: Hypoglycaemia · Monitor blood glucose and administer IV glucose if needed.
Antidotes & reversal
- Glucagon · Combined alpha/beta blockade; glucagon plus vasopressor support for significant overdose.
Clinical notes
Labetalol is used for the treatment of hypertension, including hypertensive emergencies, and is particularly favoured in pregnancy-induced hypertension. It may be given intravenously in severe hypertension. Side effects include postural hypotension, dizziness, and fatigue. It should be used with caution in patients with asthma, heart failure, or bradycardia, and is contraindicated in patients with heart block or severe asthma.
Log in to read the full labetalol monograph
A free account unlocks the complete drug reference, the interaction checker, prescription practice and every other learning tool.
BNF; local formulary