Labetalol. Current research and therapeutic status.

Labetalol hydrochloride is the prototype drug of a new class of antihypertensive agents that competitively and peripherally blocks both beta- and alpha-adrenergic receptors. It possesses approximately one fourth of the beta-blocking activity of propranolol hydrochloride and one half of the alpha-blocking activity of phentolamine. In humans, the effective beta- to alpha-blocking activity is approximately 7:1. It has been used successfully in oral form to treat patients with mild, moderate, and severe hypertension and in intravenous form to manage hypertensive emergencies. Prominent side effects include orthostatic hypotension and gastrointestinal disturbances. Overall, the drug appears to offer several advantages over pure beta-blocking drugs in some patients and should expand the armamentarium of the practicing physician in the management of the difficult hypertensive patient.