Synergic activity of teicoplanin and ethambutol against Mycobacterium tuberculosis

We have tested the in-vitro activity of teicoplanin both alone and in combination with ethambutol against clinical isolates of M. tuberculosis. The MIC was defined as the lowest concentration of antibiotic which inhibited visible growth after 21 days incubation at 37 degree C. The Fractional Inhibitory Concentration (FIC) Index was calculated from the results to determine whether the combined effect of the two drugs was synergic. On the basis of FIC Index values, ethambutol and teicoplanin clearly acted in synergy against eight of the nine strains of M. tuberculosis tested. MIC values for teicoplanin were between eight and 256 times lower when tested in the presence of ethambutol than when tested alone. Similarly, MICs for ethambutol in combination with teicoplanin were two to eight times lower than when ethambutol was used alone.