## **Core Concept**
The question tests the knowledge of side effects of antitubercular drugs, specifically their impact on thyroid function. Certain antitubercular drugs are known to interfere with thyroid function, leading to hypothyroidism.

## **Why the Correct Answer is Right**
The correct answer, , is associated with the antitubercular drug Ethionamide. Ethionamide is known to cause gastrointestinal disturbances, hepatotoxicity, and endocrine disorders, including hypothyroidism. It interferes with thyroid hormone synthesis, leading to decreased levels of T3 and T4, and can cause hypothyroidism in some patients.

## **Why Each Wrong Option is Incorrect**
* **Option A:** - This option is incorrect because while Rifampicin is known to induce the cytochrome P450 enzyme system, which can affect the metabolism of thyroid hormones, it more commonly causes hyperthyroidism or changes in thyroid function tests rather than directly causing hypothyroidism.
* **Option B:** - This option is incorrect because Isoniazid can cause pyridoxine deficiency and neuropathy but is not commonly associated with causing hypothyroidism directly.
* **Option D:** - This option is incorrect because Pyrazinamide's primary side effects include hepatotoxicity and hyperuricemia, and it is not commonly associated with thyroid dysfunction leading to hypothyroidism.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Ethionamide is one of the antitubercular drugs that can cause hypothyroidism as a side effect. Monitoring of thyroid function is recommended in patients on long-term Ethionamide therapy.

## **Correct Answer:** . Ethionamide