INCREASED IN-VITRO ACTIVITY OF CEFTRIAXONE BY ADDITION OF TAZOBACTAM AGAINST CLINICAL ISOLATES OF ANAEROBES

A total of 461 clinical strains of anaerobes were tested using a broth microdilution test to determine the activity of the combination of ce ftriaxone and tazobactam and other antimicrobials against these isolat es. Ceftriaxone was combined with tazobactam in ratios of 1:1, 2:1, 4: 1, and 8:1 and twofold dilutions of ceftriaxone in constant concentrat ions of tazobactam of 2, 4, 8, 16, and 32 mu g/ml. Against beta-lactam ase-producing strains of the Bacteroides fragilis group, B. capillosus , and Prevotella species all combinations of ceftriaxone and tazobacta m showed enhanced in vitro activity and were eight- to 2048-fold more active than ceftriaxone atone. By comparison ceftriaxone and tazobacta m showed superior or equal activity to ampicillin and sulbactam, piper acillin and tazobactam, amoxicillin and clavulanate, ticarcillin and c lavulanate, and metronidazole against these same strains. Against beta -lactamase nonproducing strains of Porphyromonas, Fusobacterium, Clost ridium, Eubacterium, Peptostreptococcus, and Veillonella parvula the a ddition of tazobactam produced no appreciable enhanced ceftriaxone act ivity. Fixed concentrations of tazobactam at 2 and 4 mu g/ml appear to be most suitable for susceptibility testing and are within the pharma cologic profile of this inhibitor. Pharmacologic and toxicity studies will be needed to define the role of ceftriaxone and tazobactam in inf ectious diseases.