February 2011

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IDSA Releases First Guidelines On MRSA

By Brian McCurdy, Senior Editor

Recognizing the rise of methicillin resistant Staphylococcus aureus (MRSA) and its role in infections acquired in the hospital and community, the Infectious Diseases Society of America (IDSA) has released its first guidelines on treating MRSA.

   The IDSA recommends that for hospitalized patients with complicated skin and soft tissue infections (cSSTI), along with surgical debridement and broad-spectrum antibiotics, one should consider empirical therapy for MRSA. Warren Joseph, DPM, notes this is a major point as the IDSA recommends that “pretty much all” patients with cSSTIs should begin anti-MRSA treatment. He says the guidelines do not give any leeway for local or regional variations in MRSA incidence.

    “Frankly, in the past six months to a year, most of our admitted patients are not growing MRSA at this point,” says Dr. Joseph, who is affiliated with the Roxborough Memorial Hospital in Philadelphia. “I have actually started going back to escalation (no MRSA empiric coverage) therapy in some cases.”

   Noting MRSA’s high prevalence, Mark Kosinski, DPM, says it is prudent to use an MRSA active agent as part of empiric therapy for severe infections. He notes that based on the culture results and clinical response, one can decide to continue or discontinue use of the antibiotic.

   “Those first few days, when you are waiting for the culture and sensitivity report to come back, can be the most critical,” says Dr. Kosinski, a Fellow of the IDSA. “Time can’t be wasted giving the wrong antibiotic. Failure to cover MRSA in a serious infection could lead to worsening of the infection and result in loss of life or limb.”

What The Guidelines Say About Vancomycin Dosing

For patients with normal renal function, the IDSA recommends IV vancomycin 15 to 20 mg/kg (actual body weight) every eight to 12 hours, and not to exceed 2 g per dose. For seriously ill patients with suspected MRSA, the guidelines call for a loading dose of 25 to 30 mg/kg (actual body weight).

   In addition, the IDSA notes trough vancomycin concentrations are the most accurate and practical method to guide vancomycin dosing. One should obtain serum trough concentrations after achieving steady state conditions, prior to the fourth or fifth dose, according to the guidelines, which do not recommend monitoring of peak vancomycin concentrations. The guidelines suggest vancomycin trough concentrations of 15 to 20 µg/mL for serious infections, such as bacteremia, infective endocarditis, osteomyelitis, meningitis, pneumonia and severe SSTI like necrotizing fasciitis due to MRSA.

    “There is essentially no good evidence to support bumping vancomycin dose/levels that high in lower extremity infections,” says Dr. Joseph, a Fellow of the IDSA.

   Dr. Joseph has a concern that many practitioners are significantly increasing vancomycin doses and maintaining troughs of 15 of 20 µg/mL despite little evidence of increased efficacy and good evidence of increased renal toxicity. He supports troughs between 10 and 15 µg/mL.

   Similarly, Dr. Kosinski questions whether vancomycin trough dosing at 15 to 20 µg/mL will cause an increase in adverse events, most notably nephrotoxicity. “This in itself may be sufficient reason to start using the host of other MRSA active agents available,” he says. “It’s time to be iconoclastic and disrupt the vancomycin gold standard status quo.”

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