Fluoroquinolone-containing third-line regimen against Mycobacterium tuberculosis in vivo

The objective of the present study was to compare the activities of a third-line regimen recommended by the World Health Organization (WHO) and two derivatives of that regimen with the activity of the standard combination of isoniazid, rifampin, and pyrazinamide as a positive control against Mycobacterium tuberculosis in a murine model. The WHO regimen combines ofloxacin (OFX), ethionamide, amikacin, and pyrazinamide; in the two derivatives of this regimen, OFX was replaced by levofloxacin (LVX) or moxifloxacin (MXF). The four drugs, a fluoroquinolone (either OFX, LVX, or MXF), ethionamide, pyrazinamide, and amikacin, were administered for the first 2 months (initial phase); and two drugs, a fluoroquinolone (either OFX, LVX, or MXF) and ethionamide, were administered for the following 10 months (continuation phase). After 6 months of treatment, only the spleens and lungs of mice treated with the standard regimen became culture negative. From 9 months onward, all of the organs of mice treated with the MXF-containing third-line regimen were culture negative. The majority of organs from mice treated with the OFX-containing regimen continued to be culture positive, and the mean CFU counts remained unchanged for as long as 12 months. The results for mice treated with the LVX-containing regimen fell between those for the groups receiving the MXF- and OFX-containing regimens. In conclusion, the activity of the OFX-containing third-line regimen against M. tuberculosis was rather weak in vivo, whereas when OFX was replaced by MXF, 9 months of treatment with a modified third-line regimen displayed bactericidal activity comparable to that of 6 months of treatment with the standard regimen in mice. The MXF-containing third-line regimen seems to be a powerful alternative for the treatment of tuberculosis (TB) when isoniazid and rifampin cannot be used, which is the main feature of multidrug-resistant TB.