## **Core Concept**
The question tests knowledge of side effects associated with anti-tubercular drugs, specifically identifying which drug causes a flu-like syndrome. This requires understanding the pharmacological profiles of various anti-tubercular medications.

## **Why the Correct Answer is Right**
Pyrazinamide is known to cause a flu-like syndrome as one of its side effects. This condition can manifest with symptoms such as fever, chills, and muscle pains, resembling influenza. Pyrazinamide acts by inhibiting fatty acid synthase I, which is essential for the synthesis of mycolic acid, a critical component of the Mycobacterium tuberculosis cell wall.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Isoniazid primarily causes peripheral neuropathy, hepatotoxicity, and optic neuritis as side effects, not a flu-like syndrome.
* **Option B:** Rifampicin is associated with hepatotoxicity, gastrointestinal disturbances, and induction of various cytochrome P450 enzymes but not typically a flu-like syndrome.
* **Option D:** Ethambutol can cause optic neuritis leading to visual disturbances but is not commonly associated with a flu-like syndrome.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Pyrazinamide is one of the first-line anti-tubercular drugs and its use can be limited by side effects such as hepatotoxicity and arthralgias, in addition to the flu-like syndrome.

## **Correct Answer:** . Pyrazinamide