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©2013 UpToDate ® Print Email Activity of antimicrobiol agents against anaerobes Agent Comments Nearly always active Metronidazole Inactive versus microaerophilic streptococci (eg, S.milleri), Propionibacterium, and Actinomyces species; bactericidal versus most gram-negative anaerobic strains Carbapenems Resistant to most Bacteroides β-lactamases, although a novel β-lactamase that cleaves carbapenems was found in rare B. fragilis strains* β-Lactam plus β-lactamase inhibitors The addition of a β-lactamase inhibitor to a β-lactam dramatically increases activity against anaerobes that produce a β-lactamase Chloramphenicol Good activity versus virtually all clinically significant anaerobes• Usually active Clindamycin B. fragilis group: 10 to 20 percent of strains resistant; some Clostridia other than C. perfringens are resistant Cefamycins B. fragilis group: 5 to 15 percent of strains resistant with considerable institutional variation at least partly reflecting use patterns; poor activity versus Clostridia Antipseudomonal Relatively resistant to β-lactamases of Bacteroides spp; penicillins large doses usually employed Variable activity Penicillin Inactive versus some or most penicillinase-producing anaerobes, including most of the B. fragilis group and many strains of Prevotella melaninogenica, P. intermedia, P. bivia, P. disiens, and some Clostridia Cephalosporins Less activity in vitro than penicillin G versus most anaerobes and limited other than cefamycins published clinical experience to document efficacy Tetracycline Inactive versus many anaerobes and most strains of B.fragilis; doxycycline and minocycline are somewhat more active than tetracycline Vancomycin Active against Gram positive anaerobes; inactive versus gram-negative anaerobes Macrolides Inactive versus many Fusobacterium spp. and some B. fragilis spp.; ketolides also show reduced activity versus Fusobacteria Fluoroquinolones Moxifloxacin is the best in this class for anaerobic infections, but the B. fragilis group shows increasing resistance and is no longer recommended in the IDSA guidelines for intra-abdominal sepsis. Tigecycline Active against nearly all anaerobes including strains of B. fragilis that are resistant to beta-lactams, clindamycin and quinolones. MICs are somewhat higher for Clostridia.Δ Poor activity Aminoglycosides Trimethoprim-sulfamethoxazole Monobactams (aztreonam)

Moxifloxacin is the best in this class for anaerobic infections, but the B. fragilis group shows increasing resistance and is no longer recommended in the IDSA guidelines for intra-abdominal sepsis. Tigecycline Active against nearly all anaerobes including strains of B. fragilis that are resistant to beta-lactams, clindamycin and quinolones. MICs are somewhat higher for Clostridia.Δ Poor activity Aminoglycosides Trimethoprim-sulfamethoxazole Monobactams (aztreonam) * Edwards, R, et al. J Antimicrob Chemother 1999; 43:273. • While in vitro activity is excellent, clinical failures with chloramphenicol have been documented, rendering this drug less preferable than other active agents for the treatment of anaerobic infections. Δ Snydman, DR, etal. J Antimcrob Chemother 2005; 55:10124.