USMLE Step 1 Question 319

Question:

A patient with newly diagnosed hypertension is treated with a medication that prevents concentration of the urine by abolishing the hypertonicity of the medulla. What area of the kidney is most likely to be affected as an adverse effect of the drug?

Correct Answer: B.  Interstitium

The medication described in the question is a loop diuretic, such as furosemide. In toxic levels, this drug can cause interstitial nephritis.

The collecting ducts and collecting tubules is the location of action for the K+-sparing diuretics and not a site of furosemide toxicity.

The action of loop diuretics occurs distal to the glomerulus and afferent arterioles and these areas are not affected by furosemide toxicity.