Antihypertensive effect of various doses of hydrochlorothiazide and its relation to the plasma level of the drug.

Nine previously untreated hypertensive patients (WHO Stage I and II) were given hydrochlorothiazide (hct) 12.5, 25, 50 and 75 mg for two weeks after an initial four week period of placebo treatment. Blood pressure recordings were made casually and after 30 min rest in lying, sitting and standing positions. Plasma concentrations of the drug were measured by GLC. A significant decrease in BP was seen during treatment with hct 12.5 mg except in the casual standing position. Doubling of the dose twice produced very little further decrease in BP. The mean steady state concentration was 111 ng.ml-1 during treatment with hct 75 mg. A linear relationship was found between the plasma concentration of hct at 0 and 5 h and the various dose level of hct. No relation was found between plasma concentration and reduction in blood pressure.