Activity of Moxifloxacin Against Ofloxacin-Resistant Mycobacterium Tuberculosis: A Study of Cross-Resistance Between Ofloxacin and Moxifloxacin

Kim, Byoung Ju; Kang, Young Soo; Park, Seung Kyu

Abstract

BACKGROUND: Moxifloxacin is an 8-methoxyquinolone compound which has been shown to have the best activity of the quinolones against M. tuberculosis but there is no literature showing the rate of cross-resistance between moxifloxacin and the other quinolones such as ofloxacin. Therefore, we tested the activity of moxifloxacin against ofloxacin resistant M. tuberculosis by a study of cross-resistance.
METHODS
We tested MIC's of moxifloxacin and ofloxacin by proportion method against 34 M. tuberculosis isolates showing resistance against ofloxacin at 2.5microgram/ml concentration and 13 ofloxacin susceptible isolates from specimens submitted to clinical laboratory of National Masan Hospital from March 2003 to March 2004.
RESULTS
For ofloxacin susceptible isolates, MIC(50) and MIC(90) of ofloxacin were all 1.25 microgram/ml, and MIC(50) and MIC(90) of moxifloxacin were 0.31 microgram/ml and 0.63microgram/ml respectively. For ofloxacin resistant isolates, MIC(50) of ofloxacin was over 10microgram/ml and MIC(50) of moxifloxacin was 5microgram/ml,MIC(90) of ofloxacin and moxifloxacin were all over 10microgram/ml. The rate of cross-resistance between the two was 67.6%(23/34) at 2.5microgram/ml concentration.
CONCLUSIONS
Moxifloxacin showed activity against 82.4%(28/34) of ofloxacin resistant M. tuberculosis at 10microgram/ml, but more studies are needed so that moxifloxacin will be used for patient with multi-drug resistant tuberculosis including ofloxacin resistance.