Factors affecting the choice of antibiotics in mixed infections.

Mixed infections can occur anywhere in the body and, on the basis of the location of the infection, involve predictable species of anaerobic bacteria. Most of our knowledge of anaerobic mixed infection has come from the study of intra-abdominal infections. The mortality associated with intra-abdominal abscesses in a recent study was lower than in earlier studies, perhaps because of improvements in radiographic techniques for better localization of abscess and early drainage, improved management of nutrition, and the selection of appropriate antimicrobial agents. The efficacy of an antimicrobial agent depends on its ability to penetrate into an abscess and function under conditions of low pH, low Eh and in the presence of beta-lactamases. Some effective antibiotics include clindamycin/gentamicin, metronidazole/gentamicin, latamoxef, cefoxitin, piperacillin and imipenem.