Reproducibility of blood pressure response to hydrochlorothiazide

Few studies have investigated the reproducibility of responses to antihypertensive therapies. The purpose of this study was to assess the reproducibility of the blood pressure response to a thiazide diuretic, a preferred initial treatment for hypertension. Twenty-two subjects who underwent monotherapy with hydrochlorothiazide as part of a study to identify predictors of blood pressure response agreed to undergo the same protocol a second time, 26.6±11.8 (range, 4-52) months after their first participation. The mean systolic and diastolic blood pressure responses to hydrochlorothiazide did not differ significantly between the first and second participation (systolic response, -14.2±l6.4 mm Hg vs. -16.0±16.5 mm Hg; diastolic response, -7.±11.8 mm Hg vs. -6.6±8.6 mm Hg), and these responses were significantly correlated between the two trials (systolic response, r=0.61 and p<0.01; diastolic response, r=0.64 and p<0.01). However, both the direction and magnitude of responses for individual subjects varied considerably, with the limits of agreement between the first and second participations (i.e., 2 standard deviations above and below the mean difference between responses) ranging from 27.4 mm Hg to -23.8 mm Hg for systolic blood pressure response and from 17.4 mm Hg to -18.4 mm Hg for diastolic blood pressure response. These results show that the average systolic and diastolic blood pressure responses to hydrochlorothiazide for a group of subjects are reproducible; however, the responses for individual subjects are unpredictable.