Which anti tubercular drug crosses the blood brain barrier (BBB)?

 # Which anti tubercular drug crosses the blood brain barrier (BBB)?

A. INH

B. Rifampicin

C. Ethambutol

D. Streptomycin

The correct answer is A. INH (Isoniazid).

Explanation:

INH (Isoniazid): 

- Crosses the blood-brain barrier (BBB) effectively, even in the absence of inflammation. 

- First-line drug for tuberculous meningitis due to excellent CSF penetration.

- Critical for treating CNS tuberculosis.

Other Options:

B. Rifampicin: Penetrates the BBB only when meninges are inflamed (e.g., in active meningitis). Not as reliable as INH under normal conditions.

C. Ethambutol and D. Streptomycin: Poor BBB penetration, making them unsuitable for CNS tuberculosis.

Key Takeaway:

INH is the most reliable anti-tubercular drug for crossing the BBB, especially in latent or early CNS infections. Rifampicin’s efficacy depends on meningeal inflammation.