## **Core Concept**
The question tests knowledge of drugs used in leprosy treatment and their side effects. Icthyosis refers to dry, scaly skin, and hyperpigmentation is a condition characterized by patches of skin becoming darker than the surrounding areas. The question requires identification of a drug used in leprosy that causes these specific side effects.

## **Why the Correct Answer is Right**
The correct answer, **C. Dapsone**, is a sulfone antibiotic used in the treatment of leprosy. One of the known side effects of dapsone is skin discoloration (hyperpigmentation) and dryness (icthyosis). Dapsone works by inhibiting the synthesis of dihydrofolic acid, which is essential for the growth of certain bacteria, including *Mycobacterium leprae*, the causative agent of leprosy.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Rifampicin is a key drug in the treatment of leprosy and tuberculosis. While it can cause a range of side effects, icthyosis and hyperpigmentation are not commonly associated with rifampicin. Its major side effects include hepatotoxicity and rifampicin resistance in tuberculosis.
- **Option B:** Clofazimine is another drug used in leprosy treatment, known for causing skin discoloration. However, the combination of icthyosis and hyperpigmentation, along with its use specifically in leprosy, makes dapsone a more fitting answer.
- **Option D:** Ethambutol is primarily used in tuberculosis treatment and is known for its potential to cause optic neuritis. It is not commonly associated with icthyosis and hyperpigmentation.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that dapsone is a critical component of multidrug therapy for leprosy and that its side effects profile includes skin manifestations like hyperpigmentation and icthyosis. This makes monitoring for such side effects crucial during treatment.

## **Correct Answer:** C. Dapsone