Anaerobic infections in small animals.

Successful antimicrobial therapy for anaerobic infections is often difficult because selection of the wrong antimicrobial drug, the presence of mixed infections, the effect of environmental conditions on antimicrobial activity, and the development of bacterial resistance contribute to therapeutic failure. Drugs that are used for the treatment of anaerobic infections include the beta-lactam antibiotics (ie, penicillins, the carbampenams, and the cephalosporins), chloramphenicol, clindamycin, metronidazole, and vancomycin. The clinical pharmacology and bacterial resistance patterns of each of these drugs determines which should be used in specific clinical situations. The penicillins remain the drug of choice for most anaerobic infections. Piperacillin, cefoxitin, chloramphenicol, clindamycin, and metronidazole are the most effective antimicrobials for the treatment of resistant Bacteroides spp. Drugs that are effective against both aerobic and anaerobic organisms, and thus are indicated as sole drugs for the treatment of mixed infections, include piperacillin, imipenem, cefoxitin and in selected instances, chloramphenicol. Drugs that may need to be combined with antimicrobials effective against gram-negative aerobes are clindamycin, narrow spectrum penicillins, and metronidazole.