Labetalol: a review of its pharmacology and therapeutic use in hypertension

Labetalol is an orally active adrenoceptor blocking drug which is a competitive antagonist at both alpha- and beta-adrenoceptor sites. Its beta-blocking effects resemble those of propranolol, but its overall haemodynamic effects are akin to those of a comination of propranolol and an alpha-adrenoceptor blocking drugs such as phenoxybenzamine. Unlike with conventional beta-adrenoceptor blocking drugs, acute administration of labetalol reduces peripheral vascular resistance and blood pressure and has little effect on cardiac output. Theoretically, labetalol has advantages over beta-adrenoceptor blocking drugs alone in the treatment of hypertension, but any real advantage, particulary in mild or moderate hypertension, has yet to be conclusively demonstrated in therapeutic trials. Labetalol may be particularly useful in some patients whose blood pressure is not adequately controlled by beta-adrenoceptor blocking drugs alone or combined with a diuretic, but possibly at the expense of a postural hypotensive effect. Postural hypotension is the most troublesome side-effect, occasionally necessitating withdrawal of therapy, but severe side-effects such as are seen with effective antihypertensive dosages of phenoxybenzamine do not occur with labetalol.