Susceptibility of multidrug-resistant strains of Mycobacterium tuberculosis to amoxycillin in combination with clavulanic acid and ethambutol.
Thirty clinical isolates of Mycobacterium tuberculosis, 20 of which were multidrug-resistant (MDR), were tested for susceptibility to different combinations of amoxycillin, clavulanic acid and subinhibitory concentrations of ethambutol. beta-Lactamase production was assessed semiquantitatively with the nitrocefin method and susceptibility testing was performed with the BACTEC method. All isolates were beta-lactamase positive and were resistant to 16 mg/L amoxycillin. The MIC of amoxycillin in combination with clavulanic acid was > or =2 mg/L for 27/30 (90%) isolates. Addition of subinhibitory concentrations of ethambutol significantly reduced the MIC of amoxycillin for all tested isolates. Twenty-nine (97%) isolates had an MIC of amoxycillin of < or =0.5 mg/L when subinhibitory concentrations of ethambutol were added; this is well below the concentrations achievable in serum and tissue.
Department of Mycobacteriology, Statens Serum Institut, Copenhagen, Denmark. hmi@ssi.dk
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D000658:Amoxicillin / Q000494:pharmacology*; D000995:Antitubercular Agents / Q000494:pharmacology*; D019818:Clavulanic Acid / Q000494:pharmacology*; D004357:Drug Synergism; D004359:Drug Therapy, Combination / Q000494:pharmacology*; D004977:Ethambutol / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000201:enzymology; D018088:Tuberculosis, Multidrug-Resistant / Q000382:microbiology; D001618:beta-Lactamases / Q000378:metabolism
D000995:Antitubercular Agents; D019818:Clavulanic Acid; D000658:Amoxicillin; D004977:Ethambutol; D001618:beta-Lactamases