Background: Although resistance to isoniazid (INH) is the most common form of drug resistance seen among Mycobacterium tuberculosis isolates, there have been few studies on the efficacy and optimal duration of treatment for patients with INH-resistant tuberculosis (TB).
Methods: We evaluated retrospectively the treatment outcomes of 39 patients who were treated for INH-resistant pulmonary TB. The treatment regimens consisted of a 12-month regimen of rifampin (RIF) and ethambutol (EMB), with pyrazinamide (PZA) given during the first 2 months (2HREZ/10RE) (n = 21), a 9-month regimen of RIF and EMB with PZA during the first 2 months (2HREZ/7RE) (n = 5), and a 6-month regimen of RIF, EMB, and PZA (2HREZ/4REZ) (n = 13). After drug susceptibility testing confirmed the INH-resistance of the isolated M. tuberculosis strains, INH was discontinued for all the patients.
Results: Among the 39 patients, treatment was successfully completed by 36 patients (92%). However, treatment failure occurred, and acquired resistance to other first-line drugs, such as RIF, developed in three patients (8%). Cavitary and bilateral extensive lesions were commonly found in the chest radiographs of the patients who exhibited treatment failure.
Conclusion: These findings underline the seriousness of concerns regarding treatment failure and the development of multidrug-resistant TB in patients with INH-resistant TB following treatment with recommended regimens.