Long-term use of which of the following diuretic agent results in gynaecomastia?
**Core Concept**
Spironolactone is a potassium-sparing diuretic that acts as an antagonist at the mineralocorticoid receptor, leading to increased levels of aldosterone. One of its notable side effects is its anti-androgenic activity, which can cause gynaecomastia in long-term use.
**Why the Correct Answer is Right**
The anti-androgenic effect of spironolactone is due to its ability to bind to androgen receptors, thereby inhibiting the action of testosterone. This leads to an imbalance in sex hormones, resulting in the development of gynaecomastia. The mechanism of action involves the blockade of dihydrotestosterone (DHT) production, which is essential for normal male sexual development.
**Why Each Wrong Option is Incorrect**
* **Option A:** Hydrochlorothiazide is a thiazide diuretic that acts on the distal convoluted tubule to increase sodium and water excretion. It does not have significant anti-androgenic effects.
* **Option B:** Furosemide is a loop diuretic that acts on the ascending limb of the loop of Henle to increase sodium and water excretion. It does not have anti-androgenic effects.
* **Option C:** Triamterene is a potassium-sparing diuretic that acts as an antagonist at the epithelial sodium channel. It does not have significant anti-androgenic effects.
**Clinical Pearl / High-Yield Fact**
Spironolactone is also used off-label for the treatment of acne, hirsutism, and androgenetic alopecia due to its anti-androgenic effects.
**Correct Answer: C. Spironolactone**