Professional and Linguistic Assessments Board (PLAB) Practice Exam

Patients with nephrogenic DI may be treated with which class of medication?

1. Antidepressants

2. Thiazide diuretics

3. Potassium-sparing diuretics

4. Loop diuretics

The correct answer is: Thiazide diuretics

Nephrogenic diabetes insipidus (DI) occurs when the kidneys do not respond adequately to antidiuretic hormone (ADH), leading to excessive urination and thirst. Thiazide diuretics, despite their action of promoting diuresis, paradoxically reduce urine output in patients with nephrogenic DI. This occurs because thiazides induce a mild volume contraction, which increases proximal tubular reabsorption of sodium and water, thus leading to increased reabsorption in the nephron and a reduced volume of urine produced. This counterintuitive effect makes thiazide diuretics a useful treatment in managing nephrogenic DI. In contrast, other choices like antidepressants, potassium-sparing diuretics, and loop diuretics do not have the same beneficial effect in this context. Antidepressants are primarily used for mood disorders and carry no specific benefit for DI. Potassium-sparing diuretics and loop diuretics typically increase urine output and would not effectively reduce polyuria associated with nephrogenic DI. Therefore, thiazide diuretics are the appropriate choice for treating patients with nephrogenic DI.