Labetalol: potent antihypertensive agent that blocks both alpha- and beta-adrenergic receptors.

Labetalol was administered as the sole antihypertensive agent to 20 ambulatory patients with mild to moderate hypertension. The mean systolic and diastolic blood pressures (+/- standard error of the mean) with the patients sitting fell significantly (P < 0.001), from 145.5 +/- 3.2 and 103.7 +/- 1.6 mm Hg respectively at the start of labetalol therapy (after a period free of antihypertensive medication) to 125.7 +/- 2.0 and 87.2 +/- 1.1 mm Hg by the end of the trial. The diastolic blood pressure was well controlled (90 mm Hg or less) with labetalol therapy in 90% of the patients. The medication was well tolerated, and no orthostatic fall in the diastolic blood pressure was observed. Pharmacologically labetalol most closely resembles a combination of a nonselective beta-adrenergic blocker like propranolol and a postsynaptic alpha-adrenergic blocker like prazosin.