Early bactericidal activity of a moxifloxacin and isoniazid combination in smear-positive pulmonary tuberculosis

Background: In vitro and animal studies have shown that moxifloxacin-containing combinations may improve the bactericidal efficacy of antituberculosis regimens. Patients and methods: We measured the decline in the sputum viable count of 13 patients who were given a combination of moxifloxacin 400 mg daily and isoniazid 300 mg daily. Results: The time required to reduce the viable count by 50% (vt(50)) was 0.38 days (95% CI -0.03-0.78 days, SEM 0.13) and the mean early bactericidal activity (EBA) was 0.60 log(10) cfu/day (95% CI 0.23-0.97, SEM 0.14). This compares with the vt(50) calculated for isoniazid and moxifloxacin alone in the same population of 0.48 and 0.88 days, respectively. The EBA values for isoniazid and moxifloxacin alone were 0.77 and 0.53 log(10) cfu/day, respectively. Conclusions: The combination of moxifloxacin and isoniazid is not antagonistic, but the combination does not significantly enhance bactericidal activity above that of isoniazid alone.