## **Core Concept**
Isoniazid is a first-line antitubercular medication used in the treatment of tuberculosis. It works by inhibiting the synthesis of mycolic acid, a critical component of the Mycobacterium tuberculosis cell wall. Like all medications, isoniazid can cause several side effects.

## **Why the Correct Answer is Right**
The correct answer, , implies that we are looking for a side effect that is NOT commonly associated with isoniazid. Isoniazid is known to cause peripheral neuropathy, hepatotoxicity, rash, and optic neuritis among other side effects.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Peripheral neuropathy is a known side effect of isoniazid, particularly due to its interference with pyridoxine (Vitamin B6) metabolism, leading to a deficiency if not supplemented.
- **Option B:** Hepatotoxicity is a significant side effect of isoniazid, and monitoring of liver function tests is recommended during treatment.
- **Option C:** Optic neuritis leading to visual disturbances is another recognized side effect of isoniazid.
- **Option D:** **Hypocalcemia** is not typically listed among the common side effects of isoniazid. Isoniazid can affect vitamin D metabolism indirectly but is more commonly associated with issues related to vitamin B6.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that isoniazid can cause peripheral neuropathy, which can be prevented by administering pyridoxine (Vitamin B6) alongside isoniazid, especially in high-risk patients. This is a high-yield fact because it directly impacts patient care and management.

## **Correct Answer:** D. Hypocalcemia