PubMed1983
Long-term therapy with oral labetalol, an alpha- and beta-blocking agent, has been shown to effectively lower blood pressure and heart rate without decreasing cardiac output. We examined the hemodynamic effects of the acute intravenous administration of labetalol in nine hypertensive patients. Labetalol (0.6 +/- 0.1 mg/kg) promptly reduced arterial pressure, heart rate, and systemic vascular resistance without change in stroke volume. Heart rate responses to passive tilt and the Valsalva maneuver were significantly blunted. With isometric exercise, heart rate and mean arterial pressure increased significantly during labetalol therapy but less than in the pre-labetalol phase. In eight patients oral labetalol therapy was continued for six weeks (mean dose 1,050 +/- 105 mg/day), and hemodynamic evaluation was repeated. During oral labetalol therapy, decreases in arterial pressure and heart rate were sustained. Systemic vascular resistance was reduced in five of the eight patients. Hemodynamic responses to tilt, Valsalva maneuver, and handgrip were similar to those during intravenous administration. Coronary blood flow decreased, but coronary as well as pulmonary vascular resistances were unchanged. These data show the efficacy of intravenously administered labetalol in lowering blood pressure and systemic vascular resistance promptly. With long-term oral therapy, decreases in blood pressure are sustained. Labetalol does not appear to have significant effects on pulmonary or coronary vascular resistances.