Harvard Heart Letter

Ask the doctor: Can I take a diuretic?

Ask the doctor

Can I take a diuretic?

Q. Over the past few years, I have needed to take hydrochlorothiazide and Lasix together. After I was hospitalized for a serious electrolyte imbalance, my doctors told me never to take these medications again. I recently had my aortic valve replaced, and am now retaining some water. Are there any diuretics I can safely take for this?

A. Hydrochlorothiazide and Lasix (the brand name for furosemide) are both "water pills," medicines that increase the production of urine. Water pills are helpful for high blood pressure, heart failure, kidney failure, or any situation where water builds up in the body. Although there are many kinds of water pills, hydrochlorothiazide and furosemide are two of the most commonly used. They act on the kidneys, which have the important job of filtering your entire blood fluid about 60 times per day.

These medications work on different parts of the kidney, forcing it to make a more dilute form of urine than it would otherwise produce. Doctors have known for decades that combining these two drugs dramatically accelerates water loss. When you lose water, though, you also lose sodium, potassium, magnesium, and other so-called electrolytes from the bloodstream. Altering the finely tuned balance of these electrolytes in the blood can throw off the electrical circuitry of the heart, which can lead to a serious heart rhythm problem. My guess is that you were hospitalized so your doctors could monitor and stabilize your heart rhythm.

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