NAPLEX (North American Pharmacist Licensure Examination) Practice Exam

Thiazide diuretics are not effective when creatinine clearance is less than?

1. 50 mL/min

2. 40 mL/min

3. 30 mL/min

4. 20 mL/min

The correct answer is: 30 mL/min

Thiazide diuretics are less effective when the creatinine clearance falls below 30 mL/min. Creatinine clearance is a measure of kidney function, indicating how well the kidneys are able to filter waste from the blood. Thiazide diuretics work primarily in the distal convoluted tubule of the nephron to promote diuresis by inhibiting sodium reabsorption. When kidney function decreases to a creatinine clearance of less than 30 mL/min, it implies significant renal impairment where the tubular function may be compromised, making thiazide diuretics less effective. Therefore, the correct answer is C (30 mL/min).