**Core Concept**
The underlying principle being tested is the prevention of tuberculosis (TB) in a high-risk neonate. **Isoniazid** is commonly used for chemoprophylaxis in individuals exposed to TB, especially in children.

**Why the Correct Answer is Right**
Isoniazid is the preferred choice for chemoprophylaxis in this scenario due to its efficacy in preventing the development of active TB. The **American Academy of Pediatrics** recommends isoniazid for at least 6 months for infants exposed to TB.

**Why Each Wrong Option is Incorrect**
**Option A:** Not provided, assuming it's not isoniazid.
**Option B:** Not provided, assuming it's not isoniazid.
**Option D:** Not provided, assuming it's not isoniazid.

**Clinical Pearl / High-Yield Fact**
It's crucial to initiate chemoprophylaxis as soon as possible in high-risk individuals, especially in neonates, to prevent the development of active TB.

**Correct Answer:** D. Isoniazid.