Beta-blocker · Alpha blocker · Antihypertensive
Labetalol
Indications
- Severe hypertension and hypertensive emergency
- Preeclampsia, eclampsia and postpartum hypertension: first-line per ACOG
- Acute ischemic stroke around reperfusion, and intracerebral hemorrhage
- Aortic dissection, slowing the heart and lowering BP with one drug
- Perioperative and postoperative hypertension
- Oral: chronic hypertension, including in pregnancy
Dosing
Infusion start: 0.5–2 mg/min, or 20 mg IV push then 20–80 mg every 10 minutes. Titration: By blood pressure.
| Where | Dose |
|---|---|
| Blood pressure boluses | Labetalol: 10–20 mg IV over 2 min; 20–80 mg every 10 min to 300 mg |
On the quick cards
Mechanism of action
Labetalol competitively blocks α1 receptors and both β1 and β2 receptors, with partial β2 agonism. α1 blockade stops norepinephrine from raising IP3 and calcium in arteriolar smooth muscle, so SVR falls, while β1 blockade prevents the reflex rise in heart rate and contractility. The β effect dominates, with an α:β ratio of about 1:3 by mouth and 1:7 IV, so BP falls with a small drop in heart rate and little change in cardiac output.
Pharmacology
- Cardiovascular: BP falls without reflex tachycardia; resting heart rate dips slightly and cardiac output changes little
- Cardiovascular: postural hypotension from α1 blockade; bradycardia, heart block and worse heart failure from β blockade
- Respiratory: β2 blockade can trigger bronchospasm
- Metabolic: hides the warning signs of hypoglycemia
- Other: crosses the placenta; newborns of treated mothers can have bradycardia, hypotension, hypoglycemia or respiratory depression
Pharmacokinetics
| Onset | IV: maximal effect within 5 min of each injection |
|---|---|
| Duration | Long: after IV dosing stops, BP takes an average of 16–18 h to return to baseline |
| Half-life | About 5.5 h IV; 6–8 h oral |
| Distribution | Large Vd, 200–800 L (McNeil 1984); crosses the placenta; little enters the brain or breast milk |
| Protein binding | About 50% |
| Metabolism | Mainly hepatic glucuronidation, with a large first-pass effect by mouth |
| Elimination | 55–60% in urine within 24 h, mostly as conjugates; the rest in bile |
| Bioavailability | About 25% orally, higher with food or liver disease |
| Dialysis | Not meaningfully removed (under 1%) |
Chemistry
- A salicylamide with an ethanolamine side chain carrying a phenylbutyl group
- Two chiral centers give four stereoisomers in equal parts: R,R (dilevalol, 25%) gives β-blockade with partial β2 agonism, S,R gives α1 blockade, and S,S and R,S are nearly inactive
- pKa 9.3 (amine): mostly ionized at pH 7.4; moderately lipophilic (log P about 3.1)
- Injection 5 mg/mL with dextrose, EDTA and methyl- and propylparaben, pH 3–4.5; protect from light and freezing
- Precipitates with 5% sodium bicarbonate
Adverse effects and cautions
In the one-pagers
- Pharmacology by Class and SuffixTraps and look-alikes: -alol (labetalol) and carvedilol block α and β.
- Obstetric EmergenciesPreeclampsia and eclampsia: Labetalol IV: 20 mg over 2 min: 40 mg, then 80 mg every 10 min; max 300 mg
- Peripheral Vascular EmergenciesCarotid endarterectomy and stenting in depth: Hyperperfusion syndrome: after a tight stenosis is opened, flow can exceed what the brain's autoregulation can handle. Signs are a severe headache on the operated side, eye or facial pain, seizures, focal deficits and confusion, usually with high blood pressure; intracerebral hemorrhage is the feared result. In the review by Zhou et al., pooled inciden
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Sources
- FDA label: labetalol HCl injection, Hospira (2023)
- McNeil 1984 (labetalol kinetics)
- ACOG Practice Bulletin 222 (2020)
- PubChem: labetalol
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow the order, the label and your institution's protocols.