Which drug is used in the initial 2-month TB treatment phase along with rifampin and pyrazinamide?

• A. Rifampin
• B. INH
• C. Pyrazinamide
• D. Ethambutol

Answer: (B)

In drug-susceptible tuberculosis, the initial two-month intensive phase uses a four-drug combination to rapidly kill bacilli and prevent resistance. That classic quartet is rifampin, isoniazid, pyrazinamide, and ethambutol.

Isoniazid is the key partner to rifampin and pyrazinamide in this phase because it is a fast-acting, bactericidal drug that specifically blocks mycolic acid synthesis in the mycobacterial cell wall. This makes it highly effective against actively dividing bacilli and helps drive down the bacterial load quickly when used together with the other agents. Ethambutol also contributes to preventing resistance and is part of the standard intensive regimen, but isoniazid is the drug most typically highlighted as the essential companion to rifampin and pyrazinamide in this context.