Research shows antibiotic prophylaxis decreases surgical site infection (SSI) rates for many procedures and is a common practice in most specialties. Even so, your facility must weigh the benefits of antibiotics against a variety of factors. Here are some guidelines for deciding when to use antibiotic prophylaxis and which drugs to select.

Assess the challenge
Despite the demonstrated efficacy of antibiotic prophylaxis, it's neither cost effective nor clinically beneficial for many procedures. No single antibiotic is effective against every potential infecting organism. Just as importantly, antibiotics have risks of their own, including allergic or toxic reactions, potential adverse interactions with other drugs and antibiotic overuse promotes bacterial resistance. Many pharmacists, including myself, recommend following the guidelines found in consensus documents such as The Medical Letter and the ASHP Therapeutic Guidelines on Antimicrobial Prophylaxis in Surgery. Many recommend prophylaxis only for procedures with high infection rates, implant cases and for patients likely to suffer serious consequences from an infection.

These guidelines emphasize that not every surgical procedure requires prophylaxis. Procedures that do require prophylactic antibiotics include prosthetic-device implantation and procedures with known high infection rates or in which a post-op infection may have serious consequences. Generally speaking, the incidence of surgical infections in outpatient cases is fairly low. This makes it difficult to assess whether a change in practice affects infection rates unless you're able to analyze many patients.

Even if you adhere to accepted sterile technique and use antibiotics, bacteria are found in about 90 percent of surgical incisions. About 2 percent to 9 percent of all surgical procedures result in infection. However, risks vary widely by the type of procedure.

Clean to dirty
I recommend using the National Research Council's (NRC) four surgery classifications to help assess the need for antibiotics. The NRC divides surgery into four categories. Each category looks at incisional wounds according to the extent of microbial contamination:

• Clean. These are primarily elective procedures and typically involve no acute inflammation and no surgical entry into the gastrointestinal (GI), genitourinary (GU), oropharyngeal, biliary or tracheobronchial tracts. There's also typically no break in aseptic technique. Examples include breast biopsy, orthopedic surgeries not involving prosthetic implants and vascular surgery. Antibiotic prophylaxis for these cases is rather controversial, as the efficacy of prophylaxis isn't well established. Infection rates with or without prophylaxis are typically less than 2 percent.
• Clean-contaminated. These are also common outpatient procedures involving controlled entry into colonized, viscous tracts (GI, GU, oropharyngeal, biliary or tracheobronchial) with minimal spillage or with minor breaks in technique that are otherwise clean. Also included in this category are re-operations on clean sites within seven days and procedures after blunt trauma. Examples include head and neck surgery, urology and GYN procedures, cholecystectomy and orthopedic surgeries involving implants. You should strongly consider antibiotic prophylaxis for these procedures, as they commonly involve endogenous flora and infection rates are about 2 percent to 10 percent in general but anywhere from 5 percent to 25 percent without prophylaxis.
• Contaminated. These include clean-contaminated procedures involving gross soiling of the operative field, major breaks in technique or surgery on open traumatic wounds less than four hours old. Examples are GU surgery in the presence of infected urine and colorectal surgery with spillage. Antibiotic prophylaxis is also the standard of care for these cases, as the general infection risk is about 10 percent to 20 percent but as high as 15 percent to 40 percent without prophylaxis.
• Dirty. Once cases move to this category, physicians no longer use antibiotics for prophylaxis but for treatment. An example would be treatment of pre-op perforation of the GI, GU, biliary or tracheobronchial tracts. Post-op infection rates are over 30 percent and can exceed 40 percent.

Choosing an agent
An effective prophylactic regimen is one that physicians direct against the most likely infecting organisms (see "Knowing the Enemy"). Endogenous organisms are those common to the procedure, while exogenous organisms are those commonly introduced secondary to breaks in sterile technique. It's impossible to eradicate every potential pathogen, however. Avoid widespread use of broad-spectrum agents, as these drugs aren't cost-effective, aren't necessarily as effective against the pathogens you're likely to encounter and their overuse promotes resistance.

The April 2004 Medical Letter antimicrobial prophylaxis guidelines say that for most procedures, cefazolin (Ancef and others) is the antibiotic of choice. The drug is active against most infections caused by skin flora (staphylococci and streptococci) and has a moderately long half-life. For colorectal procedures, nonruptured appendectomy or other surgery near the bowel, second-generation cephalosporins such as cefoxitin or cefotetan are recommended due to their anaerobic coverage.

Keep in mind that consensus guidelines are just that, guidelines. For example, cefuroxime (Ceftin) is a cephalosporin antibiotic widely used therapeutically for treating lower-respiratory infections but isn't generally recommended for prophylaxis. But it's often used this way, especially in open-heart procedures, and a fair amount of literature compares it to cefazolin for these procedures.

Other factors to consider are patient allergies and resistance patterns at your own facility (particularly at hospitals combining inpatient and outpatient surgeries in the same ORs). Long hospitalizations are associated with infections from antibiotic-resistant organisms, and risks vary by facility.

The choice of antibiotic also depends on the procedure. In ophthalmology, for example, parenteral antibiotics don't sufficiently penetrate the aqueous or vitreous humor. For these cases, most guidelines recommend a variety of topical drugs - tobramycin, gentamycin, neomycin and polymixin, and others, as well as a subconjunctival dose of either gent or tobra. Coverage is needed for both gram-positive (staph) and gram-negative (pseudomonas) bacteria. Data on the effectiveness of ophthalmic prophylaxis are quite limited. But ophthalmic prophylaxis may be a case of the potential benefits outweighing the risks, because post-op endophthalmitis can be devastating. If you do procedures that may involve exposure to bowel anaerobes (such as Bacteroides fragilis), The Medical Letter recommends IV antibiotics such as cefotetan (Cefotan) or cefoxitin (Mefoxin and others).

Current guidelines generally don't recommend such broad-spectrum agents as third- or fourth-generation cephalosporins for routine prophylaxis. The reason: They're expensive, some are less active than cefazolin against staph, the spectrum of activity includes organisms rarely encountered in elective surgery, and overuse promotes resistance. Drugs in this category include cefotaxime (Claforan), ceftriaxone (Rocephin), ceftazidime (Fortaz) and cefepime (Maxipime).

Current guidelines recommend restricting vancomycin to procedures involving prosthetic material or device implantation in patients with well-documented, life-threatening, penicillin or cephalosporin allergies in facilities experiencing post-op wound infections from widespread methicillin-resistant S. aureus and S. epidermidis.

Stand up to your docs
Physician preference cards alone aren't conclusive indicators that a case indicates using prophylaxis or a specific drug. It's helpful to identify a physician to champion a review of your facility's prophylaxis regimen, including determining if prophylactic antibiotics are administered in the appropriate time frame relative to incision. If your facility is a hospital, a physician in the infectious disease department may be an ideal candidate.

If you arm yourself with knowledge by researching the current guidelines and collecting data on your facility infection rates and timing of antibiotic administration, your surgeons will have a hard time winning an argument to defend deviating from the formulary. It's tough to produce published independent studies (not literature from drug reps) to justify not following established guidelines. Moreover, your own benchmarking data is a strong indicator of where prophylaxis is necessary.