This was created by substituting the isopropyl group in the standard beta-blocker structure with an aralkyl group, including a carboxamide group on the meta position, and by adding a hydroxyl group on the para position.Labetalol has two chiral carbons and consequently exists as four stereoisomers. Two of these isomers, the (S,S)- and (R,S)- forms are inactive. The third, the (S,R)-isomer, is a powerful α1 blocker. The fourth isomer, the (R,R)-isomer which is also known as dilevalol, is a mixed nonselective β blocker and selective α1 blocker. Labetalol is typically given as a racemic mixture to achieve both alpha and beta receptor blocking activity. Labetalol acts by blocking alpha and beta adrenergic receptors, resulting in decreased peripheral vascular resistance without significant alteration of heart rate or cardiac output. The β:α antagonism of labetalol is approximately 3:1.It is chemically designated in International Union of Pure and Applied Chemistry (IUPAC) nomenclature as 2-hydroxy-5-[1-hydroxy-2-[(1-methyl-3-phenylpropyl)amino]ethyl]benzamide monohydrochloride. Pharmacology
Mechanism of action
Labetalols dual alpha and beta adrenergic antagonism has different physiological effects in short- and long-term situations. In short-term, acute situations, labetalol decreases blood pressure by decreasing systemic vascular resistance with little effect on stroke volume, heart rate and cardiac output. During long-term use, labetalol can reduce heart rate during exercise while maintaining cardiac output by an increase in stroke volume.Labetalol is a dual alpha (α1) and beta (β1/β2) adrenergic receptor blocker and competes with other Catecholamines for binding to these sites. Its action on these receptors are potent and reversible. Labetalol is highly selective for postsynaptic alpha1- adrenergic, and non-selective for beta-adrenergic receptors.
Labetalol is a medication used to treat high blood pressure and in long term management of angina. This includes essential hypertension, hypertensive emergencies, and hypertension of pregnancy. In essential hypertension it is generally less preferred than a number of other blood pressure medications. It can be given by mouth or by injection into a vein.Common side effects include low blood pressure with standing, dizziness, feeling tired, and nausea. Serious side effects may include low blood pressure, liver problems, heart failure, and bronchospasm. Use appears safe in the latter part of pregnancy and it is not expected to cause problems during breastfeeding. It works by blocking the activation of β-receptors and α-receptors.Labetalol was patented in 1966 and came into medical use in 1977. It is available as a generic medication. In 2019, it was the 198th most commonly prescribed medication in the United States, with more than 2 million prescriptions. Medical uses
Labetalol is effective in the management of hypertensive emergencies, postoperative hypertension, pheochromocytoma-associated hypertension, and rebound hypertension from beta blocker withdrawal.It has a particular indication in the treatment of pregnancy-induced hypertension which is commonly associated with pre-eclampsia.It is also used as an alternative in the treatment of severe hypertension. Special populations
Pregnancy: studies in lab animals showed no harm to the baby. However, a comparable well-controlled study has not been performed in pregnant women.Nursing: breast milk has been shown to contain small amounts of labetalol (0.004% original dose).