Angiotensin receptor blockers and angiotensin-converting enzyme inhibitors: challenges in comparative effectiveness using Medicare data.

An evidence gap exists in comparing the effectiveness of angiotensin receptor II blockers (ARBs) for hypertension with that of angiotensin-converting enzyme inhibitors (ACEIs). We identified elderly hypertensive patients in whom ACEI/ARB therapy had been initiated after hospitalization for coronary artery disease (CAD), heart failure (HF), or stroke and who were eligible for Medicare and state pharmacy assistance programs. Of 18,801 initiators of ACEIs and 2,641 initiators of ARBs, 2,535 died during the follow-up. We observed substantial differences in characteristics between ARB and ACEI initiators, suggesting that ARB users were more health seeking. The incidence of death and sudden cardiac death (SCD) in ACEI initiators was 77 and 22 per 1,000 person-years, respectively. The relative risk for SCD comparing ARB initiators to ACEI initiators was 0.69 (95% confidence interval (CI) 0.50-0.96); when the analysis was restricted to patients with low ejection fraction (EF), the relative risk was 1.1. The reduced risk of SCD can be explained, at least partly, by (i) residual confounding because ARB users were healthier on unobserved domains and (ii) lack of data on EF.