**Core Concept**
Hepatic adaptation or microsomal enzyme induction is a process by which the liver increases the production of certain enzymes in response to certain substances, leading to increased metabolism of these substances. This adaptation is a crucial mechanism in the pharmacokinetics of various drugs.

**Why the Correct Answer is Right**
The correct answer is Isoniazid (INH), which is an antituberculous drug known to cause hepatic adaptation by inducing the cytochrome P450 enzyme system. This induction leads to an increase in the production of certain enzymes, such as NADPH-cytochrome P450 reductase and cytochrome P450 3A4, which in turn increases the metabolism of INH and other drugs. This adaptation is a result of the binding of INH to the AhR (aryl hydrocarbon receptor) and subsequent transactivation of the CYP3A4 gene.

**Why Each Wrong Option is Incorrect**
**Option A:** Rifampicin is also an antituberculous drug that causes hepatic adaptation, but it is more potent in inducing the cytochrome P450 enzyme system than INH. INH is more commonly associated with a mild increase in liver enzymes, whereas rifampicin is associated with a more significant increase.
**Option B:** Ethambutol is an antituberculous drug that is primarily excreted unchanged in the urine and does not significantly induce the cytochrome P450 enzyme system.
**Option C:** Pyrazinamide is an antituberculous drug that can cause hepatotoxicity, but it is not primarily associated with hepatic adaptation or microsomal enzyme induction.

**Clinical Pearl / High-Yield Fact**
Isoniazid-induced liver enzyme elevation is often mild and self-limiting, but it can be exacerbated by concurrent use of other drugs that induce the cytochrome P450 enzyme system, such as rifampicin.

**Correct Answer:** I. Isoniazid.