Effect of aspoxicillin on anaerobic bacteria.

Aspoxicillin (ASPC), a semisynthetic penicillin has a broad spectrum of antibacterial activities against Gram-positive and Gram-negative anaerobic bacteria. Its in vitro antibacterial activity was less than those of cefoxitin against Peptostreptococcus and Veillonella, but was significantly high against Bacteroides fragilis, one of the most clinically important anaerobe. The therapeutic and/or protective effect of ASPC in experimental subcutaneous abscess or experimental intraabdominal mixed infection due to beta-lactamase producing B. fragilis and non-producing Escherichia coli were much stronger than those of ticarcillin. In order to account the superiority of ASPC in vivo, the effects of ASPC and other beta-lactams on B. fragilis were compared and the results were analyzed in relation to their in vitro bactericidal activities, stability against the beta-lactamase, binding properties with penicillin-binding proteins and pharmacokinetic properties. Interestingly, administration of ASPC did not increase the bacterial counts of Clostridium difficile in caecal contents, but piperacillin, ticalcillin, carbenicillin, ampicillin and cefotaxime increased the counts.