Choosing an Antibiotic

An antimicrobial used in surgical prophylaxis should meet certain criteria. Selecting an antimicrobial with a spectrum that covers expected pathogens is crucial. The antimicrobial should be inexpensive, available in a parenteral formulation, and easy to use. Adverse-event potential should be minimal. Choosing an agent with a longer halflife reduces the likely need to redose unless the surgical procedure is prolonged.

Table 85-2 Major Pathogens in Surgical Wound Infections

Percentage

Pathogen

of Infections-

Siaphylococcus aureus

20

Coagulase negative stäphylococci

U

En terato cd

12

Escherichia coli

8

Pseudomonas aeruginosa

s

ir.';i•:<</,biÄ-. ia'

7

Proteus mirabiiis

3

Klebsiella pneumoniae

3

üther Sr&ptococais spp.

Candida albicans

Group 0 Streptococci

2

Other gram-positive aerobes

2

Bacreroides fragilis

2

43Data reported by the MNIS fronrr 1990 to 1996, adapted from National Academy of the 5cienc:e$ National Research Council-Postoperative wound infections: The influence of ultraviolet irradiation of the operating room and of various other factors. Ann Surg 1984; 160:3?-135.

hrom Kanji Devlin JW. Antimicrobial prophylaxis in surgery. In: DiPira JT, Talbert RL, Yee GC, et a I., (eds.) Pharmacotherapy: A Pathophysiologic Approach. 6th ed, Mew York: McGraw Hill; 2005: 2219. with permission.

Operations can be separated into two basic categories: extra-abdominal and intraabdominal. SSIs resulting from extra-abdominal operations are frequently caused by gram-positive aerobes. Thus, an antimicrobial with strong gram-positive coverage is useful. Cefazolin benefits from a benign adverse-event profile, simple dosing, and low cost. These aspects have made cefazolin the mainstay for surgical prophylaxis of extra-abdominal procedures. For patients with a P-lactam allergy, clindamycin or vancomycin can be used as an alternative.

Intra-abdominal operations necessitate broad-spectrum coverage of gram-negative organisms and anaerobes. Antianaerobic cephalosporins, cefoxitin and cefotetan, are widely used. Fluoroquinolones or aminoglycosides, paired with clindamycin or metronidazole, should provide adequate coverage for intra-abdominal operations; these regimens are recommended as appropriate regimens for use in patients with P-lactam allergies.

The Hospital Infection Control Practices Advisory Committee allows for the use of vancomycin for surgical prophylaxis when methicillin-resistant Staphylococcus aureus (MRSA) rates at an institution are "high."1 Unfortunately, a "high" rate of MRSA has not been standardized. Additionally, vancomycin use in institutions where MRSA rates are "high" may not translate into a lower incidence of SSI. Finkelstein and associates found that the incidence of SSI for patients on cefazolin or vancomycin did not differ despite a high MRSA rate at the study institution. However, patients who received cefazolin were more likely to develop an SSI due to MRSA.10 The increasing prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in patients admitted to the hospital creates an added concern, although this pathogen is often sensitive to clindamycin. Vancomycin should be considered appropriate surgical prophylaxis for those patients identified as being colonized with MRSA (prior to or at admission).1

Due to antimicrobial shortages of the recommended antimicrobials and development of newer antimicrobials (e.g., carbapenems, third and fourth generation cephalosporins, and antipseudomonal penicillins), some interest has been generated in the use of these newer antimicrobials for surgical prophylaxis. Recently, ertapenem was determined to be superior to standard cefotetan in the prevention of SSIs after elective colorectal surgery.11 However, the ertapenem treatment group had a larger proportion of Clostridium difficile infections than those in the cefotetan treatment group. Ertapenem has been included as an approved antibiotic for colon surgery by some agencies.12 At this time, it is not considered appropriate to use these newer antimicrobials for surgical prophylaxis; overuse of these antimicrobials may contribute to collateral damage and the development of bacterial resistance. Further research is needed before any of these newer agents are routinely used for surgical prophylaxis. New guidelines are likely to be published soon and may offer guidance on the use of newer antimicrobials.

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