Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the treatment for nephrogenic diabetes insipidus (DI)?

1. Amiloride

2. Desmopressin

3. Chlothiazide

4. Hydrochlorothiazide

The correct answer is: Chlothiazide

Nephrogenic diabetes insipidus (DI) occurs when the kidneys do not respond adequately to antidiuretic hormone (ADH), leading to significant water loss and increased urine output. The treatment goal is to manage symptoms by promoting water reabsorption. The use of thiazide diuretics, such as chlorthalidone and hydrochlorothiazide, despite their classification as diuretics, is effective in lowering urine output in patients with nephrogenic DI. This paradoxical effect occurs because thiazide diuretics induce a mild state of volume depletion, which can enhance proximal tubular reabsorption of water, thus reducing urine volume. This makes them a suitable treatment option as they encourage the kidneys to retain more water, counteracting the effects of nephrogenic DI. While desmopressin is effective for central DI, where there is a deficiency in ADH production, it does not work in nephrogenic DI because the kidneys lack the necessary receptors for ADH. Amiloride has been studied but primarily helps in cases of lithium-induced nephrogenic DI and is not universally effective for all cases of nephrogenic DI. Thus, thiazide diuretics remain the most effective and commonly recommended