USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

In individuals with renal failure, diuretics behave by competing for transport into the tubular lumen. This is the correct answer because diuretics work primarily in the renal tubules to inhibit sodium reabsorption, leading to increased urinary excretion of sodium and water. In individuals with renal failure, the kidneys are unable to function properly in filtering and excreting substances. Therefore, diuretics may still be used to help manage fluid overload by acting on the remaining functional nephrons in the tubular lumen.

Option A is incorrect because individuals with renal failure may have decreased urinary output and impaired renal function, resulting in a reduced ability to quickly eliminate diuretics in the urine.

Option B is incorrect because diuretics do not bind directly to the glomerulus; instead, they act predominantly in the renal tubules.

Option D is incorrect because diuretics do not have a direct impact on plasma penicillin levels.