Labetalol

Definition Labetalol is a prescription medication classified as both a non-selective beta-adrenergic blocker and a selective alpha-1 adrenergic blocker. It is primarily used to treat high blood pressure (hypertension), including severe hypertension and hypertensive emergencies. Structural Formula Labetalol.svg
Pharmacological Classification
  • Alpha-1 adrenergic blocker
  • Non-selective beta blocker (blocks both β1 and β2 receptors)
  • β: α blocking ratio: Oral: 3: 1, IV: 7: 1 → Stronger β-blockade when given IV.
 Mechanism of Action Labetalol works by:
  • Blocking β1 receptors in the heart: decreases heart rate, contractility, and cardiac output
  • Blocking β2 receptors in the lungs and blood vessels: reduces peripheral resistance.
  • Blocking α1 receptors in blood vessels: causes vasodilation, reducing blood pressure, → arterial vasodilation → ↓ systemic vascular resistance (SVR)

This combination allows labetalol to lower BP quickly without significant reflex tachycardia — a key reason it’s used in hypertensive emergencies and pregnancy-related hypertension.
Indications Hypertensive Emergency Hypertensive Urgency Acute Aortic Dissection (adjunct after esmolol) Pregnancy-related HTN (preeclampsia, eclampsia) Post-operative hypertension
Why Labetalol is Appropriate IV bolus or infusion lowers MAP rapidly → effective bedside titration Oral formulation for non-critical BP lowering Helps lower BP & HR; esmolol still preferred for rate control Safe in pregnancy; first-line with hydralazine & nifedipine Smooth control without reflex tachycardia
Dosage IV (Acute Control)  Oral
  • Bolus: 20 mg IV over 2 min → may repeat 40–80 mg q10 min (max ~300 mg total)
  • Continuous infusion: 0.5–2 mg/min; titrate to BP target
  • Initial: 100 mg PO BID
  • Maintenance: 200–400 mg BID (max up to 2,400 mg/day)
Contraindications
  • Acute decompensated HF
  • Severe asthma or bronchospasmFirst-line for rate control alone — metoprolol or esmolol preferred
  • Asthma, COPD with active bronchospasm
  • Severe bradycardia, 2nd/3rd-degree block (unless paced)
  • Cardiogenic shock / decompensated HF
  • Hypersensitivity
 Counselling
  • Take consistently (same time each day)
  • Avoid abrupt withdrawal → rebound hypertension
  • Rise slowly from sitting (orthostasis)
  • In diabetes → be aware symptoms of hypoglycemia may be masked
Adverse Drug Reaction α-blockade – emphasize slow standing β1-blockade common Rare (Uncommon)Elevated AST/ALT
Dizziness, Fatigue, Orthostatic hypotension, Bradycardia, Nausea Bradycardia Fatigue, dizziness rare; monitor liver function in chronic use
Drug – Drug Interaction Calcium channel blockers (verapamil, diltiazem) PDE-5 inhibitors Other antihypertensives Insulin/oral hypoglycemics
Additive bradycardia & AV block Severe hypotension Compounded ↓BP Masks hypoglycemia tachycardia response
Monitoring Parameters
  • Acute: BP q5–10 min when titrating, HR, respiratory status
  • Chronic: BP logs, HR, LFTs (long-term), adherence
  • Pregnancy: fetal monitoring, maternal BP goals (typically 140–155/90–105)
 Clinical Tips Labetalol is the go-to IV medication for hypertensive emergencies when rapid BP reduction is needed without tachycardia, and it is one of the safest antihypertensives for pregnancy-related hypertension.
Pharmacokinetics Route Onset Peak Duration Pharmacodynamics
  • Hepatic metabolism (glucuronidation) → adjust/caution in hepatic impairment
  • Not dialyzable
  • Minimal renal elimination → no renal dose adjustment needed
  • Crosses placenta → used intentionally in preeclampsia
IV bolus 2–5 min 5–15 min 2–6 hours
Oral 1–2 hours 1–4 hours 8–12 hours