**Core Concept**
Cystinuria is a genetic disorder characterized by the impaired reabsorption of cystine and other dibasic amino acids in the kidneys, leading to their excessive excretion in the urine. This results in the formation of cystine stones, which are difficult to treat due to their high solubility in water.

**Why the Correct Answer is Right**
The management of cystinuria involves medications that either reduce cystine excretion or increase its solubility in urine. Alpha-mercapto-propionylglycine (Alpha-MPG) is an example of a medication that reduces cystine excretion by inhibiting the transport of cystine in the kidneys. Another medication, potassium citrate, increases the solubility of cystine in urine by alkalizing the urine pH. This helps to prevent the formation of cystine stones.

**Why Each Wrong Option is Incorrect**
**Option A:** Captopril is an angiotensin-converting enzyme (ACE) inhibitor that is used to treat hypertension and heart failure. It is not indicated in the management of cystinuria.
**Option B:** Triamterene is a potassium-sparing diuretic that is used to treat edema and hypertension. It is not indicated in the management of cystinuria.
**Option C:** Allopurinol is a medication that is used to treat gout by reducing uric acid production. It is not indicated in the management of cystinuria.

**Clinical Pearl / High-Yield Fact**
In patients with cystinuria, it is essential to maintain a high fluid intake to prevent the formation of cystine stones. Additionally, medications that increase the solubility of cystine in urine, such as potassium citrate, should be used in conjunction with medications that reduce cystine excretion.

**Correct Answer:** C. Allopurinol is not indicated in the management of cystinuria.