Comparative in vitro activity of fluoroquinolones against Mycobacterium tuberculosis

Sixty clinical isolates of M. tuberculosis, 24 susceptible and 36 resistant to conventional primary antituberculous drugs, were tested against four fluoroquinolones (ciprofloxacin, ofloxacin, pefloxacin and norfloxacin). Ofloxacin and ciprofloxacin were found to be the most active, with minimum inhibitory concentration (MIC) of 0.6 mg/l or less to all strains tested. Strains resistant to isoniazid and other antitubercular drugs also showed more or less equal MICs for these two drugs. Mycobacterium tuberculosis H37 Rv showed MIC < 0.6 mg/l on each occasion. Other agents viz., norfloxacin and pefloxacin showed lesser activity against all these strains tested in comparison to ciprofloxacin and ofloxacin.