Pyrazinamide may improve fluoroquinolone-based treatment of multidrug-resistant tuberculosis.

The role of pyrazinamide in the current treatment of multidrug-resistant (MDR) tuberculosis (TB) is uncertain. From a territory-wide registry of MDR-TB cases diagnosed between 1995 and 2009, we assembled a cohort of 194 patients with MDR pulmonary TB given fluoroquinolone-containing regimens. Stratified by pyrazinamide use and susceptibility, there were 83 users with pyrazinamide-susceptible MDR-TB (subgroup A), 24 users with pyrazinamide-resistant MDR-TB (subgroup B), 40 nonusers with pyrazinamide-susceptible MDR-TB (subgroup C), and 47 nonusers with pyrazinamide-resistant MDR-TB (subgroup D). We estimated the adjusted risk ratio (ARR) of early sputum culture conversion (ARR-culture) that occurred within 90 days posttreatment and that of cure or treatment completion (ARR-success) that occurred by 2 years posttreatment due to pyrazinamide use with susceptibility. In comparison with subgroup B, ARR-culture and ARR-success were 1.38 (95% confidence interval [CI], 0.89 to 2.12) and 1.38 (95% confidence interval [CI], 0.88 to 2.17), respectively. Corresponding findings were 0.99 (95% CI, 0.81 to 1.22) and 0.99 (95% CI, 0.78 to 1.26) in comparison with subgroup C and 1.09 (95% CI, 0.84 to 1.42) and 0.94 (95% CI, 0.74 to 1.20) in comparison with subgroup D. Early culture conversion significantly increased the incidence proportion of cure or treatment completion by 71% (95% CI, 26% to 133%). Selection bias among pyrazinamide nonusers might have underestimated the role of pyrazinamide. Comparison of pyrazinamide users showed that pyrazinamide increased the incidence proportion of early culture conversion and that of cure or treatment completion by a best estimate of 38% for both. This magnitude of change exceeded the 15 to 20% increase in the 2-month culture conversion rate of drug-susceptible TB that results from adding pyrazinamide to isoniazid and rifampin. Pyrazinamide is likely important in fluoroquinolone-based treatment of MDR-TB.