Vascular effects of chlorthalidone in mild hypertensives

In a randomized trial with chlorthalidone, 30 hypertensive outpatients of both genders, aged 50.4 +/- 8.6 years, having diastolic blood pressure between 95 and 110 mm HG were divided into 2 groups of 15, after a two-week placebo period. The A group received chlorthalidone in a single dose of 23 mg for one month, and the next month was given a 12.5 mg alternative dose, whereas the B group was given 12.5 mg in the first month and 25 mg in the second. Changes in vascular reactivity were measured by occlusive plethysmography (mercury strain-gauge) at the ends of the placebo period, the first and the second month of therapy. All the observed parameters, i.e. rest flow, peak flow, venous capacity, and maximal venous outflow, were found to have increased with 25 mg chlorthalidone, and similar findings were registered when 12.5 mg of the drug were given. Venous capacity increased significantly in both groups (from 2.6 to 3.2 and from 3.0 to 3.4 ml/100 ml). The peak-flow values augmented significantly only in the group where 25 mg of chlorthalidone were given first (from 18.6 to 23.9 ml/100 ml/min). Both doses had a similar antihypertensive effect, decreasing the mean arterial pressure by some 8% in the upright, sitting, and supine position. It is concluded that the antihypertensive effect of chlorthalidone is, at least partly, due to changes in vascular reactivity; vasodilation is more prominent on the venous side of the circulation. Low-dose chlorthalidone is equipotent as antihypertensive, its side-effects are rare, and the cost of such a therapy is by far the lowest.