Why does furosemide contribute to hyponatremia?

• A. They decrease absorption of sodium
• B. They do not affect electrolyte balance
• C. They only affect potassium
• D. They increase excretion of both sodium and water

Answer: (D)

Furosemide works by blocking the Na-K-2Cl transporter in the thick ascending limb of the loop of Henle, which causes increased excretion of sodium, chloride, potassium, and water. This natriuresis together with diuresis reduces the amount of solute and water in the body. In volume-depleted states, ADH release promotes water reabsorption in the collecting ducts, which can dilute the remaining circulating sodium and lead to hyponatremia. So, the diuretic’s effect of increasing excretion of both sodium and water can lower serum sodium under the right conditions, contributing to hyponatremia.