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When used for intra-abdominal infection, aminoglycosides should be combined with agents that are effective against the majority of B. fragilis. Clindamycin or metronidazole is the agent of first choice, but others, such as antianaerobic cephalosporins (e.g., cefoxitin, cefotetan, or ceftizoxime), piperacillin, mezlocillin, and combinations of extended-spectrum penicillins with ^-lactamase inhibitors, would be suitable alternatives. Patients receiving multiple broad-spectrum antimicrobial agents who are im-munocompromised should receive an oral antifungal agent (nystatin) for prevention of fungal overgrowth in the mouth and GI tract. The benefits of systemic antifungal prophylaxis (with fluconazole) have not been established for intra-abdominal infection and should not be used routinely.

In immunocompromised patients or patients with valvular heart disease or a prosthetic heart valve, there is justification to provide specific antimicrobial activity against enterococci. Ampicillin or other penicillins that are active against enterococci (e.g., penicillin, piperacillin, and mezlocillin) should be used in patients at high-risk, patients with persistent or recurrent intra-abdominal infection, or patients who are im-munosuppressed, such as after organ transplantation. Ampicillin remains the drug of choice for this indication because it is most active in vitro against enterococci and is relatively inexpensive. Vancomycin is active against most enterococci; however, resistance is increasing, and this agent should be reserved for established infections when first-line therapies cannot be used.

IP administration of antibiotics is preferred over IV therapy in the treatment of peritonitis that occurs in patients undergoing CAPD.20 The International Society of Peritoneal Dialysis (ISPD) revised its guidelines for the diagnosis and pharmacotherapy of PD-associated infections.21 The guidelines provide dosing recommendations for intermittent and continuous therapy based on the modality of dialysis (CAPD or automated peritoneal dialysis [APD]) and the extent of the patient's residual renal function.

Antimicrobial agents effective against both gram-positive and gram-negative organisms should be used for initial IP empirical therapy for peritonitis in PD patients. The most important factors to take into consideration for initial antimicrobial selection are the dialysis center's and the patient's history of infecting organisms and their sensitivities. The use of cefazolin (loading dose [LD] 500 mg/L, maintenance dose [MD] 125 mg/L) plus ceftazidime (LD 500 mg/L, MD 125 mg/L) or cefepime (LD 500 mg/L, MD 125 mg/L) or an aminoglycoside (gentamicin-tobra-mycin LD 8 mg/L, MD 4 mg/L) is suitable for initial empirical therapy; if patients are allergic to cephalosporin antibiotics, vancomycin (LD 1,000 mg/L, MD 25 mg/ L) or an aminoglycoside should be substituted. Another option is monotherapy with imipenem-cilastin (LD 500 mg/L, MD 200 mg/L) or cefepime. Antimicrobial doses should be increased empirically by 25% in patients with residual renal function (more than 100 mL/day urine output).2 Antimicrobial therapy should be continued for at least 1 week after the dialysate fluid is clear and for a total of at least 14 days. The

reader is referred to these guidelines for additional information.

After acute bacterial contamination, such as with abdominal trauma where GI contents spill into the peritoneum, combination antimicrobial regimens are not required. If the patient is seen soon after injury (within 2 hours) and surgical measures are instituted promptly, antianaerobic cephalosporins (such as cefoxitin or cefotetan) or extended-spectrum penicillins are effective in preventing most infectious complica-

tions. Antimicrobials should be administered as soon as possible after injury.

For appendicitis, the antimicrobial regimen used should depend on the appearance of the appendix at the time of operation, which may be normal, inflamed, gangrenous, or perforated. Because the condition of the appendix is unknown preoperatively, it is advisable to begin antimicrobial agents before the appendectomy is performed. Reasonable regimens would be antianaerobic cephalosporins or, if the patient is ser iously ill, a carbapenem or ^-lactam-^-lactamase-inhibitor combination. If, at operation, the appendix were normal or inflamed, postoperative antimicrobials would not be required. If the appendix is gangrenous or perforated, a treatment course of 5 to 7 days with the agents listed in Table 77-2 is appropriate.

® Acute intra-abdominal contamination, such as after a traumatic injury, may be treated with a short course (24 hours) of antimicrobials. For established infections (i.e., peritonitis or intra-abdominal abscess), an antimicrobial course limited to 5 to 7 days is justified. Under certain conditions, therapy for longer than 7 days would be justified, for example, if the patient remains febrile or is in poor general condition, when relatively resistant bacteria are isolated, or when a focus of infection in the abdomen still may be present. For some abscesses, such as pyogenic liver abscess, antimicrobials may be required for a month or longer.

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