Choice Of Antimicrobial Agents

The suggested choice of the different antimicrobials according to the bacteria or infection site and the susceptibility of the predominant anaerobes at the suggested dose are summarized in Tables 4-7. Prophylactic therapy before surgery is generally administered when the area of surgery is expected to be contaminated by the normal mucous membrane at the operated site. Cefazolin, a first-generation cephalosporin, that has poor activity against anaerobes is generally effective in surgical prophylaxis in sites distant from the oral or rectal areas. Cefoxitin is the drug of choice in surgical prophylaxis in procedures that involve the mucous surfaces (oral, rectal, or vulvovaginal) because of its efficacy against the aerobic and anaerobic flora that reside on most mucous surfaces. The parenteral antimicrobials that can be used in most infectious sites are clindamycin, metronidazole, chloramphenicol, cefoxitin, a penicillin (i.e., ticarcillin, ampicillin) and a beta-lactamase inhibitor (i.e., clavulanic acid sulbactam), and a carbapenem (e.g., imipenem, meropenem, ertapenem). Aminoglycosides are generally added to clindamycin, metronidazole, and, occasionally, cefoxitin when treating intra-abdominal infections to provide coverage for enteric bacteria. Failure of therapy in intra-abdominal infections has been noticed more often with chloramphenicol (47), and therefore, this drug is not recommended for these infections. Penicillin is added to metronidazole in the therapy of intracranial and dental infections to cover for microaerophilic streptococci, Actinomyces spp., and Arachnia spp. A macrolide (i.e., erythromycin) is added to metronidazole in upper respiratory infections to treat S. aureus and aerobic streptococci. Penicillin is added to clindamycin to supplement its coverage against Peptostreptococcus spp. and other gram-positive anaerobic organisms.

Doxycycline is added to most regimens in the treatment of pelvic infections to provide therapy for chlamydia and mycoplasma. Penicillin is still the drug of choice for bacteremia caused by non-beta-lactamase-producing bacteria. However, other agents should be used for the therapy of bacteremia caused by beta-lactamase-producing bacteria.

Because the duration of therapy for strict anaerobic infections, which are often chronic, is generally longer than for infections due to aerobic and facultative anaerobes, oral therapy is often substituted for parenteral therapy. The agents available for oral therapy are limited and include clindamycin, amoxicillin plus clavulanic acid, chloramphenicol, and metronidazole.

Clinical judgment, personal experience with the antimicrobial agents, safety and patient compliance should direct the physician in the choice of the appropriate antimicrobial agents. The recommended antimicrobials for specific infections are discussed in each of the book's chapters.

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