indication

For the management of hypertension (alone or in combination with other classes of antihypertensive agents), as well as chronic stable angina pectoris and sympathetic overactivity syndrome associated with severe tetanus. Labetalol is used parenterally for immediate reduction in blood pressure in severe hypertension or in hypertensive crises when considered an emergency, for the control of blood pressure in patients with pheochromocytoma and pregnant women with preeclampsia, and to produce controlled hypotension during anesthesia to reduce bleeding resulting from surgical procedures.

pharmacology

Labetalol is an selective alpha-1 and non-selective beta adrenergic blocker used to treat high blood pressure. It works by blocking these adrenergic receptors, which slows sinus heart rate, decreases peripheral vascular resistance, and decreases cardiac output. Labetalol has two asymmetric centers and therefore, exists as a molecular complex of two diastereoisomeric pairs. Dilevalol, the R,R' stereoisomer, makes up 25% of racemic labetalol.

mechanism of action

Labetalol HCl combines both selective, competitive, alpha-1-adrenergic blocking and nonselective, competitive, beta-adrenergic blocking activity in a single substance. In man, the ratios of alpha- to beta- blockade have been estimated to be approximately 1:3 and 1:7 following oral and intravenous (IV) administration, respectively. The principal physiologic action of labetalol is to competitively block adrenergic stimulation of β-receptors within the myocardium (β1-receptors) and within bronchial and vascular smooth muscle (β2-receptors), and α1-receptors within vascular smooth muscle. This causes a decrease in systemic arterial blood pressure and systemic vascular resistance without a substantial reduction in resting heart rate, cardiac output, or stroke volume, apparently because of its combined α- and β-adrenergic blocking activity.

toxicity

LD₅₀ = 66 mg/kg (Rat, IV). Side effects or adverse reactions include dizziness when standing up, very low blood pressure, severely slow heartbeat, weakness, diminished sexual function, fatigue

biotransformation

Primarily hepatic, undergoes significant first pass metabolism

absorption

Completely absorbed (100%) from the gastrointestinal tract with peak plasma levels occurring 1 to 2 hours after oral administration. The absolute bioavailability of labetalol is increased when administered with food.

half life

6-8 hours

route of elimination

These metabolites are present in plasma and are excreted in the urine, and via the bile, into the feces.

drug interactions

Acetohexamide: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Chlorpropamide: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Cimetidine: Cimetidine may increase the serum concentration of labetolol by decreasing its metabolism.

Clonidine: Increased hypertension when clonidine stopped

Dihydroergotamine: Ischemia with risk of gangrene

Dihydroergotoxine: Ischemia with risk of gangrene

Disopyramide: The beta-blocker, labetolol, may increase the toxicity of disopyramide.

Enflurane: Monitor arterial pressure closely

Epinephrine: Hypertension, then bradycardia

Ergonovine: Ischemia with risk of gangrene

Ergotamine: Ischemia with risk of gangrene

Fenoterol: Antagonism

Formoterol: Antagonism

Gliclazide: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Glipizide: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Glisoxepide: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Glyburide: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Glycodiazine: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Halothane: Monitor arterial pressure closely

Ibuprofen: Risk of inhibition of renal prostaglandins

Indomethacin: Risk of inhibition of renal prostaglandins

Insulin Glargine: The beta-blocker, labetolol, may decrease symptoms of hypoglycemia.

Isoflurane: Monitor arterial pressure closely

Isoproterenol: Antagonism

Lidocaine: The beta-blocker, labetalol, may increase the effect and toxicity of lidocaine.

Methysergide: Ischemia with risk of gangrene

Orciprenaline: Antagonism

Pipobroman: Antagonism

Pirbuterol: Antagonism

Piroxicam: Risk of inhibition of renal prostaglandins

Prazosin: Risk of hypotension at the beginning of therapy

Procaterol: Antagonism

Repaglinide: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Salbutamol: Antagonism

Salmeterol: Antagonism

Terazosin: Increased risk of hypotension. Initiate concomitant therapy cautiously.

Terbutaline: Antagonism

Tolazamide: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Tolbutamide: The beta-blocker, labetalol, may decrease symptoms of hypoglycemia.

Treprostinil: Additive hypotensive effect. Monitor antihypertensive therapy during concomitant use.

Verapamil: Increased effect of both drugs