A fourth drug such as ethambutol 20 to 25 mg / kg orally once a day, ethionamide 7.5 to 10 mg / kg orally 2 times a day (or 5 to 6.67 mg / kg orally 3 times a day), or an aminoglycoside should be added if drug resistance or tuberculous meningitis is suspected or the child lives in an area where HIV prevalence among TB patients is ≥ 5%.