RESUMO
OBJECTIVE: To test the MIC of ofloxacin and levofloxacin (MIC(F) and MIC(V)) in 101 strains of Mycobacterium tuberculosis (M. tb) isolated from patients with active tuberculosis and to analyze the relation between MIC and past history of fluoroquinolones (FQs) administration. And according to the analysis of the therapeutic effect of the regimen including FQs, we want to define the resistant breakpoints of OFLX and LVFX clinically. METHOD: All isolates from sputa or pus obtained from in-patients in our hospital from Jan 1999 to Sept 2000 were tested for MIC and susceptibility. 47 patients with pulmonary tuberculosis received regimens including FQs were observed consecutively. Chi-square test was applied for the statistical analysis. RESULT: (1) The MIC(V) of 96% clinical isolates tested were 2 times lower than MIC(F). (2) The MIC(F) < 8 microg/ml and MIC(V) < 4 microg/ml were found among 91% and 92% patients without previous FQs administration, while only the MIC(F) > or = 8 microg/ml and MIC(V) > or = 4 microg/ml were found among 54% and 57% for the patients with FQs administration history. (3) If MIC(F) > or = 8 microg/ml and MIC(V) > or = 4 microg/ml were defined as the clinical resistant breakpoints, in susceptible group, the sputum negative conversion rates were 54%, 75% and 82% respectively after receiving the regimens including FQs in 3, 6, and 12 months, while 16%, 32%, and 42% respectively in resistant group, (P < 0.01). Also, there were significant differences between these two groups for chest X-ray improvements after 12 months' treatment, (P < 0.01). There were significant differences for sputum conversion rates and chest X-ray improvement between MIC(V) < 4 microg/ml and MIC(V) > or = 4 microg/ml groups (P < 0.01). CONCLUSIONS: According to the evaluation for the therapeutic effects of regimens including FQs, it is suggested that MIC(F) > or = 8 microg/ml and MIC(V) > or = 4 microg/ml be defined as resistant breakpoints clinically. The emergence of resistance to FQs in patients with tuberculosis can influence the therapeutic effects.