Okay, let's tackle this question. The user is asking about an anti-TB drug that's not toxic to the liver. First, I need to recall which TB drugs are known for hepatotoxicity. The main ones are isoniazid, rifampin, pyrazinamide, and sometimes ethambutol. Then there's streptomycin, which is injectable and maybe less hepatotoxic.

So the core concept here is hepatotoxicity of first-line anti-TB drugs. The question is testing knowledge on which drugs are safe regarding liver function. The correct answer would be a drug that's not associated with liver damage. Let me think—streptomycin is an aminoglycoside, right? It's used in TB treatment, especially in multidrug-resistant cases. Since it's given by injection, it doesn't go through the liver as much, so it's less likely to cause hepatotoxicity.

Now, the other options: Isoniazid is definitely a big one for causing liver damage. Rifampin induces liver enzymes and can lead to hepatitis. Pyrazinamide is also known for hepatotoxicity, especially in patients with alcohol use or existing liver issues. Ethambutol is more about optic neuritis than liver issues, but I think it's still generally less hepatotoxic compared to the others. Wait, but is ethambutol completely safe? Maybe not, but compared to the others, it's a minor player. However, the question is looking for the one that's "not toxic to liver". If streptomycin is an option, then it's the correct answer.

The clinical pearl here is to remember the mnemonic RIFEP for the main hepatotoxic drugs: Rifampin, Isoniazid, Ethambutol (though less), Pyrazinamide. Wait, but ethambutol isn't as commonly associated. Maybe the mnemonic is R-I-P, then? Or maybe the key is that the injectables like streptomycin are safer. So the high-yield fact is that streptomycin and other aminoglycosides are less likely to cause liver toxicity compared to the oral first-line drugs.

So putting it all together: The correct answer is streptomycin. The options A, B, C, D would need to be filled in with the drugs. Let's say the options are isoniazid, rifampin, streptomycin, ethambutol. Then the correct answer is streptomycin. Each wrong option is incorrect because they are known to cause liver damage. The clinical pearl is to remember that injectables like streptomycin have different toxicity profiles, mainly ototoxicity and nephrotoxicity, not hepatotoxicity.

**Core Concept**
Hepatotoxicity is a significant adverse effect of first-line antitubercular drugs. The question tests knowledge of drugs in the TB regimen and their organ-specific toxicity profiles, particularly focusing on liver safety.

**Why the Correct Answer is Right**
**Streptomycin**, an aminoglycoside antibiotic, is administered parenterally and is not metabolized by the liver. It bypasses hepatic metabolism entirely, making it non-hepatotoxic. Its primary toxicities are ototoxicity and nephrotoxicity, not liver injury. This distinguishes it from other first-line TB drugs like isoniaz

✓ Correct Answer: D. Streptomycin