## **Core Concept**
Bacteriostatic antitubercular drugs inhibit the growth and multiplication of *Mycobacterium tuberculosis* without killing the bacteria directly. These drugs are crucial in treating tuberculosis (TB) as part of combination therapy.

## **Why the Correct Answer is Right**
Ethionamide works by inhibiting the synthesis of mycolic acid, an essential component of the mycobacterial cell wall. This action is bacteriostatic, meaning it stops the growth of the bacteria rather than killing them outright. Ethionamide is used in combination with other drugs for the treatment of tuberculosis.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Isoniazid is a bactericidal drug, not bacteriostatic. It works by inhibiting the synthesis of mycolic acid, leading to the disruption of the bacterial cell wall and ultimately killing the bacteria.
* **Option B:** Rifampicin is also a bactericidal drug. It inhibits RNA synthesis by binding to the beta-subunit of RNA polymerase in the bacteria, which leads to the death of the bacteria.
* **Option D:** Streptomycin is an aminoglycoside antibiotic that is bactericidal against *M. tuberculosis*. It works by inhibiting protein synthesis through binding to the bacterial ribosome.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that bacteriostatic drugs like Ethionamide require a combination of drugs for TB treatment to prevent the development of drug resistance. Ethionamide can cause gastrointestinal side effects and hepatotoxicity, similar to other antitubercular drugs.

## **Correct Answer:** C. Ethionamide