Acute hemodynamic effects of labetalol in severe hypertension.

Intravenous injection of labetalol induced an immediate fall (-22.4%) in blood pressure (BP) in 11 patients with severe hypertension. Hypotensive episodes were avoided by repeated injections of 0.2-0.8 mg/kg. The pressure reduction was associated with a mean fall in total peripheral resistance of 13.6%. Cardiac output fell 10.1% owing to a fall in heart rate of 10.8%, while stroke volume remained virtually unchanged. Despite excellent acute control of BP by intravenous injection, oral labetalol alone or in combination with hydrochlorothiazide was not effective in long-term treatment of these patients with severe hypertension. After 1 week, mean arterial pressure was still 10.4% below the pretreatment level, but after 4 months BP was back to pretreatment level in all except one patient whose BP is still well controlled after more than 2 years on labetalol.