Over 1 million Veterans are prescribed a thiazide-type diuretic each year; over 95% receive hydrochlorothiazide, and fewer than 2.5% receive chlorthalidone. Both medications are thiazide-type diuretics that have been used for more than 50 years and are considered first-line treatment for hypertension. Indirect evidence has been accumulating, however, that chlorthalidone may be more effective than hydrochlorothiazide at preventing cardiovascular events. This will be the first randomized head-to-head comparison of the effectiveness of these two drugs. The study plans to enroll 13,500 Veterans over 3 years and follow them on average for 3 years, resulting in a total study duration of 4.5 years. Patients currently prescribed hydrochlorothiazide will be randomized to either continue taking hydrochlorothiazide or to receive an equivalent dose of chlorthalidone. The unique 'point of care' or 'clinically integrated' study design will identify, enroll and follow subjects using the electronic medical record system and national VA and non-VA databases. The primary outcome is an event composite consisting of: stroke, myocardial infarction, non-cancer death, urgent revascularization, and hospitalization for acute congestive heart failure. All patient care, including the study drug, will continue to be managed by the primary care provider.~Primary Care Providers will also be included as participants in this research study. Adding providers as subjects will allow us to study the implementation of the point of care protocol design in addition to the original research question. The study team will collect data on diuretic management within the study and may contact providers by phone or email to learn reasons for declining a particular patient or discontinuing a new chlorthalidone order or an ongoing diuretic prescription.~If cardiovascular events are reduced by even a small amount by chlorthalidone, the public health effect will be considerable because of the large number of patients who take diuretics. A randomized trial, now feasible due to the investigators' efficient and inexpensive design, will provide evidence needed to better inform practice throughout the VA.
The purpose of this study is to determine whether chlorthalidone is more effective than hydrochlorothiazide at preventing cardiovascular outcomes in Veterans over age 65 with hypertension. Both medications are thiazide-type diuretics that have been used for more than 50 years and are considered first-line treatment for hypertension. Patients currently prescribed hydrochlorothiazide will be randomized to either continue taking hydrochlorothiazide or to receive chlorthalidone, and followed for major cardiovascular events, such as myocardial infarction (MI) and stroke. The study will use a new, efficient and less expensive study design termed 'point of care', in which study operations will be conducted centrally and patient data will be collected passively through the electronic medical record.