Per-Protocol Analysis of Chlorthalidone Versus Hydrochlorothiazide for Cardiovascular Event Prevention—Diuretic Comparison Project

BACKGROUND: The DCP (Diuretic Comparison Project), a pragmatic trial, evaluated whether chlorthalidone compared with hydrochlorothiazide would reduce the risk of nonfatal cardiovascular disease or noncancer-related death. The intent-to-treat analysis found no difference in such comparison (hazard ratio, 1.04 [95% CI, 0.94–1.16]). The objective of the current study is to estimate the per-protocol effect of chlorthalidone (12.5/25 mg daily) compared with hydrochlorothiazide (25/50 mg daily) in preventing major adverse cardiovascular events among older patients with hypertension. METHODS: The effect of adhering to treatment strategies was assessed by censoring at first instance of nonadherence, defined as a gap (>90-day gap in drug coverage), switch (switching between study medications), and discontinuation (stop taking chlorthalidone/hydrochlorothiazide altogether for >90 days before the end of the study). The primary outcome was a composite of nonfatal myocardial infarction, stroke, heart failure resulting in hospitalization, urgent coronary revascularization for unstable angina, and noncancer-related death. Using inverse probability weighting, we evaluated the per-protocol effect of chlorthalidone and hydrochlorothiazide using DCP trial data. RESULTS: Nonadherence was found in 5476 (40%) participants; among 8047 (60%) adherents, 3905 (49%) were randomized to chlorthalidone and 4142 (51%) to hydrochlorothiazide. After censoring time when participants deviated from the assigned treatments, the estimated 5-year risk ratio of the composite primary outcome of nonfatal cardiovascular disease and noncancer-related death was 1.36 (95% CI, 0.96–2.12) in chlorthalidone compared with hydrochlorothiazide. CONCLUSIONS: The per-protocol analysis indicated a lower risk with hydrochlorothiazide compared with chlorthalidone in preventing nonfatal cardiovascular disease and noncancer-related death; however, this difference was not statistically significant using dispensation data to identify adherence.