One widely used diuretic may reduce potassium more than another

People who began taking the blood pressure medicine chlorthalidone were more likely to develop low potassium than those who started hydrochlorothiazide in a large analysis of U.S. health records. The comparison also raised concerns about kidney effects, though a later randomized study was more reassuring on that issue.

Both drugs are diuretics, often known as water pills. They lower blood pressure partly by helping the kidneys remove salt and water, which can also alter mineral levels in the blood.

In a study led by Columbia University and published in JAMA Internal Medicine, researchers used three databases covering more than 730,000 people who started one of the two medicines as their first blood pressure treatment.

The investigators looked at heart attack, stroke and hospitalization for heart failure. After adjusting for measurable differences between patients, they found no clear difference between the two groups in the combined rate of major cardiovascular events.

The potassium findings were more striking. In one database, about 6.3% of chlorthalidone users had documented low potassium, compared with 1.9% of hydrochlorothiazide users. Across the databases, the adjusted rate was about 2.7 times higher with chlorthalidone.

Potassium supports nerve and muscle function and helps maintain a regular heart rhythm. A drop may be detected on a blood test, and larger decreases can be especially important for people with existing heart rhythm problems.

Along with blood tests, follow-up care can include home blood pressure checks to help lower stroke risk.

The same study associated chlorthalidone with more cases of low sodium, sudden kidney problems and chronic kidney disease. Because doctors selected the treatment, differences in why one drug was prescribed instead of the other could have affected those comparisons.

A later analysis of a randomized Veterans Affairs trial also found more low potassium with chlorthalidone. However, it did not find a clear difference in worsening kidney disease or in hospitalizations for acute kidney injury.

The two studies involved different patient groups. The health records analysis followed people starting either drug, while the trial assigned older patients already taking hydrochlorothiazide to continue it or switch. That difference helps explain why the results do not match exactly in every detail.

Taken together, the studies provide stronger evidence about potassium than about whether one drug is more likely than the other to harm the kidneys over time. How important those findings are depends on a patient’s other conditions, medicines and blood test results.

For patients prescribed a diuretic, the results help explain why clinicians may check potassium and kidney function after starting treatment or changing a dose. Those tests guide care alongside the patient’s blood pressure response.

If you are interested in this topic, please read articles about Eating More Potassium Rich Foods May Help Lower Blood Pressure Better Than Cutting Salt Alone, and How High Blood Pressure Can Damage Your Kidneys and Heart Without Warning.

For more information, please see articles about Can Common Blood Pressure Drugs Prevent Second Heart Attack, and How Common Blood Pressure Drugs Affect Sleep and Mental Health.

Source: Columbia University Irving Medical Center.