**Core Concept**
Rifampicin is a key component of the Revised National Tuberculosis Control Programme (RNTCP) in India, used to treat tuberculosis (TB). The correct dose of rifampicin is essential for effective treatment and to prevent resistance.

**Why the Correct Answer is Right**
The RNTCP guidelines recommend a dose of 450 mg rifampicin twice a week, given in combination with isoniazid, pyrazinamide, and ethambutol. This dosing regimen is based on the principle of intermittent dosing, which helps maintain therapeutic levels of the drug in the body while minimizing side effects. The 450 mg dose is specifically chosen to balance efficacy and safety, allowing for effective TB treatment while minimizing the risk of adverse effects.

**Why Each Wrong Option is Incorrect**
**Option A:** 600 mg is an excessive dose, which could increase the risk of adverse effects such as hepatotoxicity, gastrointestinal upset, and flu-like symptoms. Higher doses of rifampicin are not recommended in the RNTCP guidelines.
**Option C:** 300 mg is a suboptimal dose, which may not provide sufficient bactericidal activity against Mycobacterium tuberculosis. Lower doses may lead to treatment failure or the development of resistance.
**Option D:** 100 mg is an extremely low dose, which is unlikely to achieve therapeutic levels of rifampicin in the body. This dose would be ineffective in treating TB.

**Clinical Pearl / High-Yield Fact**
To remember the correct dose of rifampicin in RNTCP, recall the "2-4-6" rule: 2 times a week, 450 mg (4.5 times the standard adult dose), and 6 months of treatment duration.

**✓ Correct Answer: B. 450 mg**