Hepatotoxic drug used in tuberculosis is ?
**Core Concept**
Isoniazid is a first-line antitubercular agent, and hepatotoxicity is a well-documented side effect. This question tests the student's knowledge of the pharmacological properties of isoniazid and its potential to cause liver damage.
**Why the Correct Answer is Right**
Isoniazid is hepatotoxic due to its ability to induce the metabolism of acetyl-CoA by inhibiting the enzyme pyridoxal kinase. This leads to the formation of acetyl-CoA, which is then converted to acetylated isoniazid, a reactive metabolite that depletes glutathione levels in the liver. The resulting oxidative stress and depletion of glutathione levels cause liver damage, leading to hepatotoxicity. This mechanism is also related to the role of the cytochrome P450 enzyme system and the involvement of the NADPH-dependent cytochrome P450 reductase.
**Why Each Wrong Option is Incorrect**
* **Option A:** Rifampicin is another antitubercular agent but is not primarily known for its hepatotoxicity. While rifampicin can cause liver enzyme elevations, it is not typically associated with severe hepatotoxicity like isoniazid.
* **Option B:** Ethambutol is an antitubercular agent that is primarily associated with optic neuritis as a side effect, not hepatotoxicity.
* **Option C:** Pyrazinamide is another first-line antitubercular agent, but while it can cause liver enzyme elevations, it is not as strongly associated with hepatotoxicity as isoniazid.
**Clinical Pearl / High-Yield Fact**
When using isoniazid for the treatment of tuberculosis, it is essential to monitor liver enzyme levels regularly, especially in patients with pre-existing liver disease or those taking other hepatotoxic medications.
**Correct Answer:** C. Isoniazid