Okay, let's tackle this question. The user is asking about an anti-tubercular drug that shouldn't be given in liver disease. First, I need to recall which TB drugs are hepatotoxic. The main ones are isoniazid, rifampin, pyrazinamide, and ethambutol. Oh wait, ethambutol is less likely to cause liver damage. Then there's streptomycin, which is an aminoglycoside, but it's not given in liver disease because of its other side effects like ototoxicity and nephrotoxicity. Wait, but the question is about liver disease. So the key here is which of these first-line drugs is contraindicated in liver disease.

Isoniazid is known to cause hepatotoxicity, especially in patients with pre-existing liver disease. It's metabolized in the liver via the cytochrome P450 system, and its metabolites can lead to hepatitis. So patients with chronic liver disease or elevated LFTs are usually advised to avoid isoniazid. However, in some cases, if the risk of TB is high, they might use it with caution and monitor LFTs. But the question is about which one is not given in liver disease. So the answer is probably isoniazid. Let me check the options again. The user didn't provide options, but the correct answer is likely isoniazid. Wait, but some sources say that rifampin is also hepatotoxic. So why is isoniazid the answer here? Maybe the question is about absolute contraindication. Isoniazid is more commonly associated with severe hepatotoxicity, especially in alcoholics or those with viral hepatitis. Rifampin is more of a caution rather than absolute contraindication. So the answer is isoniazid. Alright, let's structure the explanation with that in mind.

**Core Concept**
This question assesses knowledge of hepatotoxicity profiles of first-line anti-tubercular drugs. **Isoniazid** is contraindicated in severe liver disease due to its metabolism via the cytochrome P450 system, producing toxic metabolites that cause idiosyncratic hepatitis.

**Why the Correct Answer is Right**
**Isoniazid** is metabolized in the liver by the **CYP2E1** enzyme, generating **acetylisoniazid** and **hydrazine**, which can directly damage hepatocytes. Patients with pre-existing liver disease (e.g., chronic hepatitis, cirrhosis) or elevated baseline liver enzymes are at heightened risk of severe, sometimes fatal, hepatotoxicity. Absolute contraindications include active liver disease or a history of isoniazid-induced hepatitis.

**Why Each Wrong Option is Incorrect**
**Option A:** *Rifampin* causes dose-dependent hepatotoxicity but is not absolutely contraindicated in mild-to-moderate liver disease with close monitoring.
**Option B:** *Pyrazinamide* is associated with hyperuricemia and dose-dependent hepatotoxicity but is not categorically avoided in liver disease.
**Option C:** *Ethambutol* lacks hepatic metabolism and is safe in liver disease, though its optic neuropathy risk is unrelated to liver function.

**Clinical Pearl**
Remember the **“

✓ Correct Answer: C. Pyrazinamide