What is the primary risk of taking Lasix (furosemide)?

• A. Hypokalemia
• B. Hyperkalemia
• C. Hyponatremia
• D. Hypernatremia

Answer: (A)

Loop diuretics like furosemide block the Na-K-2Cl transporter in the thick ascending limb of the loop of Henle, which causes a large amount of sodium and water to be excreted. This increased delivery of sodium to the distal nephron drives more potassium out into the urine, so blood potassium levels commonly fall. That potassium loss is the primary, clinically important risk of taking Lasix, because hypokalemia can cause muscle cramps, weakness, and dangerous heart rhythm disturbances.

Hyponatremia and dehydration can occur with diuretics as well, but they are not the main or most characteristic risk. Hyperkalemia would be more typical of medications that reduce potassium excretion or increase potassium intake, not of loop diuretics. Keep an eye on potassium levels and consider supplementation or a potassium-sparing strategy if needed.