Treatment outcome of patients with isoniazid mono-resistant tuberculosis

Isoniazid mono-resistance is the most common first-line drug resistance in tuberculosis (TB), but its treatment outcome remains unclear. From January 2004 to October 2011, 425 (5.1%) of 8414 patients with culture-confirmed pulmonary TB from four hospitals in Taiwan were identified as having isoniazid mono-resistant TB. Among them, 395 (92.9%) were included and followed up for 2 years after complete treatment. Although 328 (83.0%) patients were successfully treated, 67 (17.0%) had unfavourable outcomes, including death in 56 (14.2%) and treatment failure in 11 (2.8%). The treatment success rate was similar in patients with high-level and low-level isoniazid-resistant TB (82.2% versus 83.4%, p 0.785) and among those taking anti-TB treatment with and without isoniazid (83.1% versus 83.0%, p 1.000). Patients without rifampicin interruption had lower risk of unfavourable outcome (14.3% versus 37.0%, p <0.001), especially those with low-level isoniazid resistance (11.5% versus 56.5%, p <0.001). Supplementation with a new-generation fluoroquinolone improved treatment success (60.0% versus 12.5%, p 0.003). The presence of cavitary lesions was significantly associated with a higher relapse rate (4.1% versus 0.0%, p 0.006) and extended treatment of 7–9, 10–12 and >12 months had less relapse than 6-month treatment (3.2%, 0%, 3.7% and 25.0%, respectively, p 0.037). Multivariate Cox proportional hazards analysis revealed that co-morbidity with cancer (hazard ratio, 2.43) and rifampicin interruption (hazard ratio 1.91) were independent factors associated with unfavourable outcomes. Treatment throughout with rifampicin and extended treatment for cavitary disease are crucial for improving outcomes in patients with isoniazid mono-resistant TB.