infectious diseases
Mixed Anaerobic Infections
Treatment of Mixed Anaerobic Infections
Drainage and debridement Antibiotic choice varying by site of infection In established infection, pus is drained, and devitalized tissue, foreign bodies, and necrotic tissue are removed. Organ perforations must be treated by closure or drainage. Whenever possible, blood supply should be reestablished. Septic thrombophlebitis may require vein ligation as well as antibiotics. Because anaerobic culture results may not be available for 3 to 5 days, antibiotics are started empirically. Antibiotics sometimes work even when some of the bacterial species in a mixed infection are resistant to the antibiotic (eg, because of loss of support from other bacterial species or the necrotic anaerobic environment), especially if surgical debridement and drainage are adequate. Antibiotics are chosen based on infection site and thus likely organisms. Oropharyngeal anaerobic infections may not respond to penicillin and thus require an antibiotic effective against penicillin-resistant anaerobes (see below). Oropharyngeal infections and lung abscesses should be treated withclindamycinor a beta-lactam/beta-lactamase inhibitor combination such asamoxicillin/clavulanate. In patients allergic to penicillin,clindamycinormetronidazole(plus an antibiotic active against aerobes and microaerophiles) is useful. GI or female pelvic anaerobic infections are likely to contain obligate anaerobic gram-negative bacilli such asB. fragilisplus facultative gram-negative bacilli such asEscherichia coli; antibiotic regimens must be active against both. Resistance ofB. fragilisand other obligate anaerobic gram-negative bacilli to penicillins and 3rd- and 4th-generation cephalosporins occurs. However, the following antibiotics have excellent in vitro activity againstB. fragilisand are effective: Metronidazole Carbapenems (eg,imipenem/cilastatin,meropenem,ertapenem,doripenem) Beta-lactam/beta-lactamase combinations (eg,piperacillin/tazobactam,ampicillin/sulbactam,amoxicillin/clavulanate) Tigecycline Moxifloxacin No single regimen appears to be superior. Antibiotics that are less predictably active in vitro againstB. fragilisincludeclindamycin,cefoxitin, andcefotetan. Metronidazoleis active againstclindamycin-resistantB. fragilis, has unique anaerobic bactericidal activity, and usually avoids the pseudomembranous colitis sometimes associated withclindamycin. Concerns aboutmetronidazole's potential mutagenicity have not been of clinical consequence. Because many regimens currently used to treat GI or female pelvic anaerobic infections (see also Treatment ) are also effective against facultative gram-negative bacilli, use of a potentially nephrotoxic aminoglycoside (to cover enteric facultative gram-negative bacilli) plus an antibiotic active against 