**Core Concept**
Ethambutol, a first-line anti-tubercular medication, is associated with optic neuritis and peripheral neuropathy. However, another anti-tubercular drug can cause transient memory loss due to its effects on the central nervous system.

**Why the Correct Answer is Right**
Pyrazinamide, a key component of the standard anti-tubercular regimen, has been linked to the development of transient memory loss and liver enzyme elevations. This is thought to occur due to its ability to induce the synthesis of new liver enzymes, leading to an increase in liver function tests and potentially causing transient cognitive impairment. The exact mechanism is not fully understood but may involve the inhibition of mitochondrial function.

**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid is primarily associated with peripheral neuropathy due to pyridoxine deficiency, not transient memory loss.
**Option B:** Rifampicin is known for its effects on the liver, but it is not typically linked to transient memory loss.
**Option C:** Ethambutol can cause optic neuritis and peripheral neuropathy, but it is not the primary cause of transient memory loss.

**Clinical Pearl / High-Yield Fact**
Pyrazinamide-induced liver enzyme elevations can be mitigated by monitoring liver function tests and adjusting the dose as needed. Additionally, patients should be counseled on the importance of adhering to the prescribed regimen to minimize the risk of treatment failure.

**Correct Answer:** D. Pyrazinamide