In vitro activity of azlocillin, metronidazole and its hydroxy metabolite against anaerobes. Bacteriostatic synergism studies.

H Werner, G Schädler, C Krasemann

Index: Arzneimittelforschung 33(4) , 574-7, (1983)

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Abstract

The in vitro inhibitory activity of azlocillin (Securopen), metronidazole (Cloni) and its hydroxy metabolite was determined against 27 gram-negative and 13 gram-positive species of anaerobes by means of agar dilution tests. The 63 anaerobic strains were also tested against the pairs azlocillin-metronidazole and azlocillin-hydroxy metabolite by means of agar dilution tests. Gram-negative species (Bacteroides spp., Fusobacterium spp. etc.) were inhibited by 0.125-256 micrograms/ml azlocillin, 0.01-4 micrograms/ml metronidazole and 0.01-4 micrograms/ml hydroxy metabolite. With gram-positive anaerobes (Clostridium spp., Peptococcaceae etc.) the MIC ranges were 0.125-4 micrograms/ml for azlocillin, 0.03-1 micrograms/ml for metronidazole and 0.125-2 micrograms/ml for the hydroxy metabolite. A synergistic effect was observed exclusively with gram-negative anaerobes (Bacteroides fragilis, B. thetaiotaomicron, B. disiens etc.). There were few instances of antagonism, likewise with gram-negative species. The preponderant combination effect against gram-positive anaerobes was addition. In view of the broad antiaerobic spectrum of azlocillin, the present in vitro findings do not preclude combined therapy with metronidazole in cases of anaerobic-aerobic poly-bacterial infections.