Antihypertensive effect and plasma levels of labetalol. A comparison with propranolol and dihydrallazine.

Seventeen outpatients suffering from essential hypertension were treated in a double-blind cross-over study with labetalol or with a combination of propranolol and dihydrallazine. The doses were increased depending on the response during the six week treatment periods. Both treatments reduced the blood pressure significantly as compared to the placebo, and the combination more than labetalol with the doses used, apparently because of a higher degree of the beta-blockade. Positive linear correlations were found between the dose of labetalol and the concentration in plasma as well as the concentration of labetalol in plasma and the decrease of standing blood pressures.