Labetalol- α- β-adrenergic blocking drug

Labetalol

PHARMACODYNAMICS

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.

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.

PROTEIN BINDING

50%

SIDE EFFECTS

A light-headed feeling, like you might pass out;

slow heart rate, weak pulse, fainting, slow breathing (breathing may stop);

shortness of breath (even with mild exertion), swelling, rapid weight gain;

METABOLISM

Primarily hepatic, undergoes significant first pass metabolism

ROUTE OF ADMINISTRATION

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

HALF LIFE

6-8 hours

DRUG DRUG INTERACTION

Acepromazine + Labetalol = Acepromazine may increase the hypotensive activities of Labetalol.

Acetaminophen + Labetalol =The risk or severity of adverse effects can be increased when Labetalol is combined with Acetaminophen.

Acetylcholine + Labetalol =The risk or severity of adverse effects can be increased when Labetalol is combined with Acetylcholine.

Acetylsalicylic acid + Labetalol =The risk or severity of adverse effects can be increased when Labetalol is combined with Acetylsalicylic acid.

Aldesleukin + Labetalol = The risk or severity of adverse effects can be increased when Aldesleukin is combined with Labetalol.

USES

Labetalol is a beta-blocker that affects the heart and circulation (blood flow through arteries and veins).

Labetalol is used to treat hypertension (high blood pressure).

Reference- Tripathi KD "Essential of medical pharmacology" 7th edition, page no- 144,148,151,564,573