Which medication is not part of the initial three-drug regimen described for active TB?

Which medication is not part of the initial three-drug regimen described for active TB?

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

Answer: (D)

The key idea is that initial therapy for active, drug-susceptible TB starts with a core three-drug combination, with one drug added only as a safeguard until drug-susceptibility results come back. The three essential partners are isoniazid, rifampin, and pyrazinamide. Ethambutol is included only when there’s uncertainty about resistance (until susceptibility results are known) to provide extra coverage. Once tests show the strain is susceptible to isoniazid and rifampin, Ethambutol can be dropped and the regimen continues with the three core drugs. So Ethambutol is not part of the initial three-drug regimen described.

The key idea is that initial therapy for active, drug-susceptible TB starts with a core three-drug combination, with one drug added only as a safeguard until drug-susceptibility results come back. The three essential partners are isoniazid, rifampin, and pyrazinamide. Ethambutol is included only when there’s uncertainty about resistance (until susceptibility results are known) to provide extra coverage. Once tests show the strain is susceptible to isoniazid and rifampin, Ethambutol can be dropped and the regimen continues with the three core drugs. So Ethambutol is not part of the initial three-drug regimen described.