Do I need to take a potassium supplement if I am on a diuretic?

Q. I started retaining extra fluid. My doctor just prescribed Lasix. Do I need to take extra potassium?

A. Lasix is the brand name for furosemide, It's an example of a loop diuretic. Another example of a frequently prescribed loop diuretic is torsemide (Demadex). Doctors most often prescribe this type of water pill for people who retain a lot of water. A common reason is heart failure.

Loop diuretics cause the kidneys to make more urine. But they also cause the kidneys to lose potassium along with the extra urine.

Whether you need to take extra potassium depends on how you respond to the Lasix. Some people lose very little potassium in response to loop diuretics. Others lose a lot of potassium.

Your doctor will likely want you to have a blood test to check your potassium level sometime soon. If your potassium is low, your doctor will prescribe a potassium supplement.

So, don't just start taking extra potassium. Get advice from your doctor about taking potassium pills or eating more potassium-rich foods.

There are reasons to be cautious about taking extra potassium. It can be dangerous if your kidneys don't function normally. Also, some medicines interfere with the kidneys' normal potassium excretion. If you also start a potassium supplement, it can lead to a dangerougly high potassium blood level. Examples of these drugs include:

• the potassium-sparing diuretics spironolactone (Aldactone) and eplerenone (Inspra)
• angiotensin-converting enzyme (ACE) inhibitors such as lisinopril and many others
• angiotensin receptor blockers such as losartan, valsartan, and many others.

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