Comparing clinical effectiveness and drug toxicity with hydrochlorothiazide and chlorthalidone using two potency ratios in a managed care population.

This study compared the clinical effectiveness and drug toxicity of chlorthalidone and hydrochlorothiazide. Electronic health records and claims data were used to identify patients initially prescribed chlorthalidone or hydrochlorothiazide. A total of 214 patients prescribed chlorthalidone 25 mg were matched with 428 patients prescribed hydrochlorothiazide 25 mg (1:1 potency ratio) and 214 patients prescribed hydrochlorothiazide 50 mg (1:2 potency ratio). Mean systolic blood pressure/diastolic blood pressure values at least 30 days after initial prescription were lower with chlorthalidone (132.2/74 mm Hg) compared with hydrochlorothiazide 25 mg (137.0/77.5 mm Hg) and hydrochlorothiazide 50 mg (138.6/78.5 mm Hg) (P<.05 for all comparisons). Goal systolic blood pressure/diastolic blood pressure values were achieved in a higher percentage of patients prescribed chlorthalidone (45.0%/78.3%) than with either hydrochlorothiazide 25 mg (32.1%/63.9%) or hydrochlorothiazide 50 mg (32.8%/68.9%) (P<.05 for all comparisons). Mean serum potassium was 3.94 mEq/L with chlorthalidone 25 mg, 4.13 mEq/L with hydrochlorothiazide 25 mg (P<.01 vs chlorthalidone), and 3.96 mEq/L with hydrochlorothiazide 50 mg. These findings indicate that chlorthalidone 25 mg is associated with a better antihypertensive response than hydrochlorothiazide 25 mg or 50 mg, without clinically significant differences in serum potassium.