Blood pressure, plasma volume, extracellular volume and glomerular filtration rate during treatment with labetalol in essential hypertension.

In 17 patients with essential hypertension administration of labetalol alone resulted in a significant reduction in supine systolic and diastolic blood pressure of 14% and 17%, respectively. Seven patients attained a diastolic pressure less than equal to 95 mmHg. A significant postural fall in systolic blood pressure was recorded, but no symptomatic orthostatic hypotension occurred. Pulse rate decreased significantly by 8%. Side effects were few causing only two withdrawals. In twelve patients plasma volume (125I-albumin), extracellular volume (82Br-distribution space) and glomerular filtration rate (51Cr-EDTA clearance) were measured during a placebo period and on labetalol alone given for an average of 3 months and 3 weeks. Plasma volume and extracellular volume increased insignificantly by 5% and 4%, respectively. Glomerular filtration rate was unchanged. In conclusion, this study showed that labetalol given alone to patients with mild or moderate essential hypertension resulted in significant, persistent and clinically relevant reductions in blood pressure without concomitant fluid retention or influence on glomerular filtration rate.