This proposed pilot study will test methods and feasibility for a large pragmatic clinical trial comparing two inexpensive, first-line drugs for treating high blood pressure to determine if one is superior in preventing serious cardiovascular events and death. It will develop and test novel approaches to conducting trials that will be faster, less expensive, and more realistic by being embedded in a typical practice setting and using advanced health information technology.

For several decades, U.S. hypertension treatment guidelines have recommended a low-dose diuretic such as hydrochlorothiazide (HCTZ) or chlorthalidone (CTD) as initial monotherapy in a stepped-care approach or as part of an initial two-drug combination. In numerous large clinical trials, CTD-based regimens have significantly reduced rates of cardiovascular events such as stroke, heart failure, and cardiovascular mortality compared with placebo, usual care, or active comparators. In contrast, few outcome studies have compared HCTZ-based regimens with other treatments, and they have generally found HCTZ to be less effective than non-thiazide comparators in preventing cardiovascular events. The two drugs have never been compared directly in a large trial. Despite the empirical evidence favoring CTD, HCTZ is much more widely used in clinical practice. The proposed R34 is a pilot study conducted in two large integrated health systems to test methods and feasibility for an eventual pragmatic randomized trial comparing the effectiveness of HCTZ and CTD for preventing cardiovascular events and mortality. Using a cluster-randomized design, investigators will allocate 40 primary care physicians and their adult hypertensive patients who currently use HCTZ (N=2,000) to either convert HCTZ users to CTD (intervention group) or to continue HCTZ (usual care group). The pilot study and planned full-scale trial will use existing health care infrastructure and electronic health records to identify eligible study subjects, distribute study medication, and collect operational and outcomes data. For this pilot study, Aim 1 will document that the intervention is delivered as intended. Aim 2 will compare safety in intervention and usual care patients. Aim 3 will refine the pilot study design and identify critical factors for intervention success using a mixed-methods approach. Aim 4 will refine estimates of sample size. Finally, Aim 5 will determine the costs of ascertaining outcomes and estimate per-participant costs for the full-scale trial. The pilot study will produce data that are necessary and sufficient to inform the planning of a full-scale trial comparing CTD and CTZ and will advance the development of methods for pragmatic trials.

Inclusion Criteria:

• Adults 18 years and older
• Hypertension diagnosis (ICD-9 401.x)
• Current prescription for hydrochlorothiazide (HCTZ), 12.5-50 mg/day as a single-agent (not part of a fixed-dose combination drug)
• No history of intolerance to chlorthalidone (CTD)
• No known low levels of sodium (<135 mEg/L (milliequivalents per liter)) or potassium (<3.5 mEg/L)
• English speaking

Exclusion Criteria:

• Physician deems patient inappropriate for switching HCTZ to CTD
• Patient refuses the switch prior to intervention