Antibiotic treatment is usually administered after cultures have been taken but before any results are available. The choice should be reviewed when culture results have been obtained, and an agent with the narrowest effective spectrum should be selected to reduce the pressure for emergence of resistance ( Table..!.). Unfortunately, the pathogen causing the infection may not be demonstrated or the cultures may be mixed or negative. The treatment should be continuously reviewed to continue, stop, or modify coverage for the most likely pathogens.
Table 1 Recommended antibiotic treatment for patients in the ICU
The presence of pulmonary consolidation or an abdominal collection of purulent material will often direct treatment of bacteremia. Without an obvious focus, a parenteral cephalosporin (cefuroxime, cefotaxime, or ceftriaxone) will be effective against the majority of likely causes unless the patient has had a prolonged hospital stay or previous antibiotics. Alternatively, amoxicillin-clavulanate (co-amoxiclav) or penicillin plus an aminoglycoside could be used. If the patient is hypotensive, the addition of an aminoglycoside, usually gentamicin, will improve the bactericidal activity of therapy but will not alter the antibacterial spectrum. If anaerobes are suspected, metronidazole or clindamycin should be added. Neither cephalosporins nor aminoglycosides are active against streptococci or enterococci, and a glycopeptide may be required in hospitals where methicillin-resistant Staph. aureus is common. Each microbiology laboratory should maintain lists of blood culture isolates so that the most likely species and recent sensitivity patterns are available to guide treatment ( Fig 1).
Fig. 1 Causative organisms in 300 surgical patients with septic shock. (Data from Shoemakerefa/ (1,993).)
Patients with sepsis following abdominal or pelvic surgery may suffer a polymicrobial bacteremia and will require a broad-spectrum regimen such as cefuroxime and metronidazole either with or without gentamicin. An alternative is clindamycin plus gentamicin.
Patients developing a febrile episode during neutropenia or immune suppression are likely to have pseudomonal infection and should be treated without awaiting cultures. Ceftazidime, ciprofloxacin, or piptazobactam are common choices. Imipenem or meropenem have a wide spectrum of activity and are better reserved as second-line therapy. Gram-positive bacteremia is common, and is usually caused by coagulase-negative staphylococci seeded from long-term central venous catheters. These organisms are usually susceptible only to glycopeptides, and some argue that vancomycin or teicoplanin should form part of the initial regimen. However, Gram-positive bacteremia in these patients is rarely fatal, and outcome is similar if a glycopeptide is not started for 48 h when the effects of the initial antibiotic should be apparent. If there are signs of inflammation at the exit site, glycopeptides should be given immediately. Failure to respond to initial therapy, particularly in the presence of infiltrates on the chest radiograph, should prompt the addition of amphotericin B because of the likelihood of infection with Aspergillus or Candida species. Conventional formulations should be used unless the patient has previously experienced adverse effects with the agent or is developing renal failure.
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