Evidence suggests that chlorthalidone may be superior to hydrochlorothiazide (HCTZ) for treating hypertension, but new findings show that chlorthalidone use in older adults is associated with a greater incidence of electrolyte abnormalities, especially hypokalemia, compared with HCTZ, according to a report in Annals of Internal Medicine (2013;158:447-455).

Both drugs were associated with similar incidences of adverse cardiovascular events or deaths over up to five years of follow-up.

In an observational cohort study, Irfan A. Dhalla, MD, MSc, of St. Michael’s Hospital in Toronto, and colleagues included 29,873 hypertensive patients aged 66 years or older who were not hospitalized for heart failure, stroke, or myocardial infarction (MI) in the previous year. They matched 10,384 chlorthalidone recipients to 19,489 HCTZ recipients on the basis of age, gender, year of treatment initiation, and propensity score.

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The primary outcome—a composite of death or hospitalization for heart failure, stroke, or MI—occurred at a rate of 3.2 events per 100 person-years of follow-up in the chlorthalidone arm and 3.4 events per 100 person-years of follow-up in the hydrochlorothiazide arm. Compared with the HCTZ group, however, chlorthalidone recipients had a 3.06 times and 1.68 times greater likelihood of being hospitalized for hypokalemia and hyponatremia, respectively.