Time to Sputum Culture Conversion and Treatment Outcomes among Patients with Isoniazid-Resistant Tuberculosis in Atlanta, Georgia

Abstract

Background Although isoniazid-resistant tuberculosis is more common than multidrug-resistant tuberculosis, it has been much less studied. We examined the impact of isoniazid resistance and treatment regimen, including use of a fluoroquinolone, on clinical outcomes. Methods A retrospective cohort study among patients with sputum culture-positive tuberculosis was performed. Early fluoroquinolone (FQ) use was defined as receiving ≥5 doses during the first month of treatment. The primary outcome was time to sputum culture conversion (tSCC). A multivariate proportional hazards model was used to determine the association of isoniazid resistance with tSCC. Results Among 236 patients with pulmonary tuberculosis, 59 (25%) had isoniazid resistance. The median tSCC was similar for isoniazid-resistant and -susceptible cases (35 vs 29 days; P =.39), and isoniazid resistance was not associated with tSCC in multivariate analysis (adjusted hazard ratio = 0.83; 95% confidence interval [CI],.59-1.17). Early FQ use was higher in isoniazid-resistant than -susceptible cases (20% vs 10%; P =.05); however, it was not significantly associated with tSCC in univariate analysis (hazard ratio = 1.48; 95% CI,.95-2.28). Patients with isoniazid-resistant tuberculosis were treated with regimens containing rifampin, pyrazinamide, and ethambutol + a FQ for a median of 9.7 months. Overall, 191 (83%) patients were cured. There was no difference in initial treatment outcomes; however, all cases of acquired-drug resistance (n = 1) and recurrence (n = 3) occurred among patients with isoniazid-resistant tuberculosis. Conclusions There was no significant association with isoniazid resistance and tSCC or initial treatment outcomes. Although patients with isoniazid-resistant tuberculosis had a high cure rate, the cases of recurrence and acquired drug resistance are concerning and highlight the need for longer-term follow-up studies.