First-line drugs in TB RIPE regimen are?

• A. Isoniazid, rifampin, pyrazinamide, and ethambutol
• B. Rifampin, isoniazid, ethambutol, and erythromycin
• C. Isoniazid, rifampin, rifabutin, ethambutol
• D. Isoniazid, rifampin, pyrazinamide, and streptomycin

Answer: (A)

The main idea here is recognizing the standard initial TB treatment combo, known as RIPE, which uses four drugs with complementary actions to rapidly reduce bacterial load and prevent resistance. The four drugs are isoniazid, rifampin, pyrazinamide, and ethambutol. Isoniazid blocks mycolic acid synthesis in the mycobacterial cell wall and is highly bactericidal against actively growing bacilli, but it can quickly select for resistance if used alone. Rifampin inhibits bacterial RNA synthesis by targeting RNA polymerase, providing strong bactericidal activity. Pyrazinamide works in the acidic environments inside macrophages and lesions to kill dormant, non-replicating bacilli, helping sterilize persistent organisms. Ethambutol interferes with cell wall synthesis, adding another mechanism that also helps prevent resistance when used with the others.

This combination is favored because it attacks the bacteria from multiple angles, reduces the chance of resistance developing, and is well supported by evidence for initial intensive therapy. After the two-month intensive phase, treatment typically continues with rifampin and isoniazid for several more months, depending on the clinical scenario.

The other options introduce drugs not used as part of the standard first-line four-drug regimen (for example, some are alternative rifamycins or drugs not effective against TB), so they aren’t the recommended first-line set.