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Debunking 6 Antibiotic Prescribing Myths
Find out how to better protect your patients against bacterial infection.
Dianne Taylor
Publish Date: June 9, 2008   |  Tags:   Infection Prevention
Research shows that as many as two-thirds of surgical patients receive ?inappropriate' antibiotic prophylaxis, which can increase the probability of surgical wound infection nearly 2.5-fold over ?appropriate' prophylaxis and promote antimicrobial resistance. This comes as no surprise to infectious disease experts, who say misconceptions about how to prescribe antibiotics are rampant. In this article, two experts tackle the top antibiotic prophylaxis prescribing misconceptions and explain how to better protect your patients against bacterial infection.

Misconception #1
Clean Procedures Don't Need Prophylaxis
Many practitioners believe that the majority of ?clean' procedures - that is, those that do not involve trauma or inflammation or enter the respiratory, alimentary, genital or urinary tract - do not warrant prophylaxis. This is because current prescribing guidelines focus on procedure type as the primary criterion for prophylaxis, and they indicate prophylaxis for only a few clean procedures. According to the Centers for Disease Control, for example, the two established indications for prophylaxis during clean procedures are those involving a prosthetic material (such as ACL and hernia repairs) and those in which a surgical site infection (SSI) would pose "catastrophic risk" (cardiac operations, for example).

The problem with this paradigm, advises infectious disease expert Robert Condon, MS, MD, FACS, is that patient factors also increase the risk of SSI. To truly minimize the risk of infection, he says, surgeons should also consider patient risk factors as indications for prophylaxis. They include: Longer procedures, older age, obesity and systemic disease. Any American Society of Anesthesiologists' (ASA) rating greater than II increases the risk of SSI; this includes any patient with mild systemic disease, such as controlled hypertension.

Misconception #2
Administer Prophylaxis Any Time Perioperatively
Although it seems reasonable to administer prophylaxis any time during the perioperative period, it is not, according to infectious disease experts. Proper timing of administration is critical, and research shows that many clinicians administer antibiotics too early or too late to be effective. The period of risk for SSI begins with the incision, and the goal of prophylaxis is to achieve and maintain a maximum inhibitory concentration in serum (MIC 90) just prior to the incision and throughout the period of operative manipulation, says Samuel E. Wilson, MD, Professor and Chair of the Department of Surgery at the University of California, Irvine. Although the exact time needed for an antibiotic to reach an effective tissue concentration depends on its pharmacokinetic profile and route of administration, the rule of thumb for most outpatient procedures is to administer antibiotics intravenously within 30 minutes of induction of anesthesia. For antibiotics that move rapidly through tissues - like beta-lactams (including cephalosporins) and the broad-spectrum quinolones - administration should occur later rather than sooner, preferably right along with induction, says Dr. Condon. "You don't want to give the dose too early and have the serum level dissipate before the patient gets to the OR," adds Dr. Wilson.

Antimicrobial Resistance: What it Means to You



Misconception #3
Continue Coverage After Wound Closure
One of the most widespread prescribing misconceptions is the belief that the longer the antibiotic coverage, the better. To the contrary, studies consistently show that there is no clinical benefit to extending prophylactic antibiotic coverage beyond the point of wound closure - even in trauma patients with contaminated wounds. The postoperative inflammatory process, says Dr. Condon, effectively ?walls off' the wound to antibiotic penetration. Therefore, a single, well-timed preoperative dose almost always offers the best protection against infection in the outpatient setting. Typically, this is all that is needed to keep the pathogenic microbial load in check, explains Dr. Condon, since prophylaxis is not an attempt to sterilize tissues but is intended to reduce the microbial burden of intraoperative contamination to a level that cannot overwhelm host defenses. A second intraoperative dose may be warranted only when using a short-acting antibiotic like ampicillin-sul-bactam and the procedure runs longer than 2 or 3 hours.

Besides lack of efficacy, antimicrobial resistance is another good reason to avoid prolonged prophylaxis. After approximately 24 hours, antibiotics kill off enough of the normal flora and susceptible pathogenic bacteria in the patient to allow room for any antibiotic-resistant bacteria to survive and multiply, explains Dr. Wilson. According to Dr. Condon, this ?selective antibiotic pressure' allows the resistant bacteria to divert enzyme systems otherwise used as a defense against competing bacterial colonies and use them to destroy antibiotics. However, once the antibiotic leaves the body and the normal flora return, the resistant bacteria no longer have the upper hand. In fact, they are disabled in the face of these competitive bugs because their usual enzyme systems are no longer intact. The fact that single-dose prophylaxis does not induce selective pressure in the first place explains why it is safe and does not increase the risk of antimicrobial resistance in patients. "It is important to understand," says Dr. Condon, "that resistant bugs require antibiotic pressure to persist."

Misconception #4
Newer Antibiotics Are Better Than Older Ones
Because cefazolin isn't always effective for treating established infection, many assume it's ineffective as prophylaxis. Not so, says Dr. Condon. Prophylaxis and treatment are two very different animals. Since the pathogenic bacterial load is typically much lower during the course of a clean operation than it is in an established infection, older antibiotics like cefazolin typically do a sufficient job of controlling the pathogenic bacterial load during clean outpatient procedures.

Although it may be tempting to use a newer antibiotic to ensure efficacy, Dr. Condon advises against it. For all clean procedures in which Staphylococcus aureus is the likely pathogen, first-generation cephalosporins like cefazolin should be standard prophylaxis. Whenever anaerobes are also likely pathogens, as in the case of intra-abdominal surgery, Dr. Condon recommends adding metronidazole to the prophylactic regimen. For patients undergoing elective colorectal procedures, preoperative oral bowel preparation is also necessary. "Both cefazolin and metronidazole carry infinitesimally small risks," adds Dr. Condon. The only time a different agent may be warranted is when the surgeon is treating a known carrier of resistant bacteria.

Outpatient Cephalosporin Prophylaxis: The Preponderance of Evidence



Misconception #5
Orthopedic Procedures Warrant Vancomycin
Because orthopedic procedures often involve prostheses, orthopedic surgeons are among the most frequent users of prophylactic antibiotics. These surgeons typically used methicillin for routine prophylaxis, but a sharp rise in the number of methicillin-resistant S. aureus (MRSA) infections led many to switch to vancomycin. But prolonged vancomycin prescribing has caused a rapid rise in vancomycin-resistant enterococci, and this is of particular concern to infectious disease specialists because enterococci can transfer their ability to resist vancomycin to other bacterial species, including S. aureus. In fact, some strains of S. aureus already appear to be at least partially resistant to vancomycin, which has been the last remaining line of defense against MRSA bacteria.

For this reason, the American Association of Orthopedic Surgeons recommends reserving vancomycin prophylaxis for patients undergoing joint replacement at institutions with a high prevalence (10 to 20 percent, for example) of methicillin-resistant S. aureus and S. epidermidis, and limiting this prophylactic regimen to two doses. For the outpatient facility, Dr. Condon recommends against third-generation cephalosporin prophylaxis altogether. When used improperly or filtered into the environment, these antibiotics can worsen the problem of resistance, he notes. Experts agree that the presence of a prosthesis does not in itself justify prophylaxis with a third-generation cephalosporin. "First-generation cephalosporins are still the lynchpin for prophylaxis in clean surgery where there is a prosthetic implant," notes Dr. Wilson.

Misconception #6
Cultures Are Unnecessary
Although not all surgeons think it's necessary, they should perform a culture whenever an SSI occurs, advises Dr. Wilson.

Experts agree this is the best way to keep tabs on the health of your facility's environment. "It's likely that the ?common' infecting organisms will change from time to time, and the best way to know what you're dealing with is to take a culture," says Dr. Wilson.

A safer future
With the rise of antimicrobial resistance, confusion has infused the practice of antibiotic prescribing. By differentiating between prophylaxis and treatment, gaining a basic understanding of the issue of resistance and knowing the risk factors for SSI, however, you can safely and effectively protect your patients against infection.

Contact Dianne Taylor at [email protected].

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