Antihypertensive effectiveness of very low doses of hydrochlorothiazide: results of the PHICOG Trial.

A large, multicenter, randomized, placebo-controlled, double-blind trial was carried out to determine the effects of the lowest dose of commercially available hydrochlorothiazide. Thus, Dyazide (which contains 25 mg of hydrochlorothiazide and 50 mg of triamterene in an approximately 50% bioavailable form), one capsule, was given daily to patients with either mild or moderate hypertension (supine diastolic blood pressure of 95 to 115 mmHg) for eight weeks. At the end of this eight-week period, supine diastolic blood pressure (SDBP) fell by 11.3 +/- 6.7 mmHg (mean +/- SD) in the Dyazide-treated compared to 4.6 +/- 6.9 mmHg in the placebo-treated group (P less than 0.001). In two thirds of the patients receiving active treatment the fall in SDBP was more than 10 mmHg, and in over half SDBP was completely normalized (ie, SDBP less than 90 mmHg). Supine systolic blood pressure fell by 14.7 +/- 12.3 mmHg in the Dyazide-treated group compared to 5.3 +/- 11.6 mmHg in the placebo-treated group (P less than 0.001). Approximately 80% of the antihypertensive effect occurred within two weeks and after four weeks there was no further significant reduction. Mildly (SDBP = 95 to 104 mmHg) and moderately (SDBP = 105 to 115 mmHg) hypertensive patients responded similarly to treatment. All studied subpopulations responded to treatment with a reduction of SDBP of at least an average of 10 mmHg; the best responders were blacks, women, the elderly (greater than 65 years old), and patients weighing less than 170 lbs. Side effects were mild and infrequent. In conclusion, by examining the effects of Dyazide (one capsule/day), this investigation demonstrated the effectiveness of low-dose hydrochlorothiazide in antihypertensive therapy and quantified it both in the general population and in clinically relevant subpopulations.