The extent of a patient’s TB disease is important in determining appropriate regimen options, in addition to the drug susceptibility of the M. tuberculosis and other considerations mentioned above. Patients with extensive disease are not eligible for the 9-month all-oral regimen with either linezolid or ethionamide.
Patients with severe extrapulmonary MDR/RR-TB are not eligible for a 9-month regimen with either linezolid or ethionamide. The 9-month regimen may also not be adequate therapy for patients with osteoarticular or pericardial MDR/RR-TB. Poor penetration of first-line TB drugs through the pericardial tissues leads to low pericardial drug concentrations compared with plasma (44), and although definitive data are lacking, drug penetration remains a concern for second-line TB drugs also. Treatment outcomes among patients treated with longer regimens for osteoarticular MDR/RR-TB are encouraging (45), and there is evidence that linezolid penetrates bone tissue well (46). However, due to the general lack of data on the efficacy of shorter regimens for treatment of these extrapulmonary manifestations of MDR/RR-TB, it remains prudent to treat such patients with longer regimens. In children and young adolescents aged below 15 years, extrapulmonary forms of disease other than lymphadenopathy (peripheral nodes or isolated mediastinal mass without airway compression) are considered to be severe (47) and might not be adequately treated with the 9-month all-oral regimen.