New York—Even though current treatment guidelines recommend chlorthalidone over hydrochlorothiazide when a diuretic is required to treat hypertension, a new study cautions about increased serious side effects with the preferred medication.

The report in JAMA Internal Medicine details how patients prescribed chlorthalidone had nearly three times the risk of developing dangerously low levels of potassium and a greater risk of other electrolyte imbalances and kidney problems, as opposed to those taking hydrochlorothiazide.

Columbia University Irving Medical Center–led researchers report that, based on their database study, 6.3% of patients treated with chlorthalidone experienced hypokalemia, compared with 1.9% of patients treated with hydrochlorothiazide. Furthermore, they point out, hypokalemia rates remained elevated for patients on chlorthalidone even when the dosage was lower than hydrochlorothiazide.

“Doctors prescribing chlorthalidone should monitor for certain side effects in their patients,” recommended lead author George Hripcsak, MD, MS, chair and Vivian Beaumont Allen Professor of Biomedical Informatics at Columbia University Vagelos College of Physicians and Surgeons.

The authors describe how chlorthalidone is currently recommended as the preferred thiazide diuretic to treat hypertension, but no trials have directly compared risks and benefits. In response, they sought to compare the effectiveness and safety of chlorthalidone and hydrochlorothiazide as first-line therapies for hypertension in real-world practice.

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