Meta-Analysis of Dose-Response Characteristics of Hydrochlorothiazide and Chlorthalidone: Effects on Systolic Blood Pressure and Potassium

BACKGROUND Evidence supporting the benefit of low-dose thiazide-based regimens to reduce cardiovascular events is primarily derived from studies using chlorthalidone, yet low-dose hydrochlorothiazide (HCTZ) (12.5-25 mg) remains more widely prescribed. We sought to describe their comparative dose-response relationships for changes in systolic blood pressure (SBP) and potassium. METHODS PubMed from 1948 to July 2008 was systematically searched to identify clinical trials using either HCTZ or chlorthalidone monotherapies. A total of 108 clinical trials with HCTZ and 29 with chlorthalidone were analyzed. Data were pooled to evaluate the effects on SBP and potassium of both drugs throughout their respective dose-response curves. Equivalence analysis was performed for the clinically recommended low-dose range of 12.5-25 mg, grouped by study duration, using the two one-sided tests procedure described by Schuirmann. RESULTS When evaluated on a milligram-per-milligram basis using pooled data, chlorthalidone generally produces slightly greater reductions in SBP and potassium than HCTZ. In the low-dose range of 12.5-25 mg, equivalence analysis reveals that the reductions in SBP are not equivalent between the two drugs, using upper and lower equivalence bounds of 4 mm Hg. Within the same dosing range, the mean changes in potassium were determined to be equivalent when upper and lower equivalence bounds of 0.29 mEq/l are used. CONCLUSIONS Equivalence analysis using data from several studies suggests that the SBP reductions achieved with HCTZ and chlorthalidone cannot be considered equivalent within the low-dose range currently recommended. However, within this dosing range, reductions in potassium can be considered equivalent.