Bacteriostatic anti – TB drug is
**Core Concept**
Bacteriostatic agents are compounds that inhibit the growth and multiplication of microorganisms, but do not necessarily kill them. In the context of tuberculosis (TB), bacteriostatic drugs can slow down the growth of Mycobacterium tuberculosis, but the bacteria may remain viable and resume growth when the drug is discontinued.
**Why the Correct Answer is Right**
The correct answer is **Ethionamide**. Ethionamide is a second-line anti-TB medication that works by inhibiting the synthesis of mycolic acid, a critical component of the mycobacterial cell wall. By disrupting mycolic acid production, ethionamide prevents the bacteria from forming a stable cell wall, ultimately leading to a bacteriostatic effect. Ethionamide is often used in combination with other anti-TB drugs to treat drug-resistant TB cases.
**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid is a bactericidal agent that directly kills Mycobacterium tuberculosis by inhibiting the synthesis of mycolic acid.
**Option B:** Rifampicin is also a bactericidal agent that works by inhibiting RNA synthesis in mycobacteria.
**Option C:** Streptomycin is an aminoglycoside antibiotic that is bactericidal against Mycobacterium tuberculosis, but its use is limited due to the risk of ototoxicity and nephrotoxicity.
**Clinical Pearl / High-Yield Fact**
When choosing an anti-TB regimen, it's essential to consider the patient's previous treatment history, drug resistance patterns, and potential side effects of the medications. Ethionamide is often used in combination with other second-line drugs, such as para-aminosalicylic acid (PAS) and cycloserine, to treat complex TB cases.
**Correct Answer: D. Ethionamide**