title: The standard one gram dose of vancomycin is not adequate prophylaxis for MRSA.
abstract: BACKGROUND
  The indications for vancomycin prophylaxis to prevent Methicillin-resistant Staphylococcus aureus (MRSA) surgical site infections are increasing. The recommended dose of vancomycin has traditionally been 1 gram intravenous. However, the increasing prevalence of obesity in our population coupled with increasing resistance of MRSA to vancomycin has resulted in recent recommendations for weight-based dosing of vancomycin at 15 mg/kg. We hypothesize that the standard one gram dose of vancomycin is inadequate to meet the recently recommended dosage of 15 mg/kg.
  
  
  METHODS
  We performed a retrospective chart review on 216 patients who were screened positive for MRSA prior to undergoing elective total joint or spine surgeries between January 2009 to January 2012. All patients were given 1 gram of vancomycin within an hour prior to surgical incision as prophylaxis. Using the revised dosing protocol of 15 mg/kg of body weight for vancomycin, proper dosage was calculated for each patient. These values were then compared to the 1 gram dose given to the patients at time of surgery. Patients were assessed as either underdosed (a calculated weight-based dose >1 gram) or overdosed (a calculated weight-based dose <1 gram). Additionally, we used actual case times and pharmacokinetic equations to determine the vancomycin (VAN) levels at the end of the procedures.
  
  
  RESULTS
  Out of 216 patients who tested positive for MRSA, 149 patients (69%) were determined to be underdosed and 22 patients (10%) patients were determined to be overdosed. The predicted VAN level at the end of procedure was <15 mg/L in 60% of patients with 1 gram dose compared to 12% (p=0.0005) with weight base dose. Six patients developed post-operative MRSA surgical site infections (SSI). Of these six patients; four had strains of MRSA with vancomycin minimum inhibitory concentration of >1.0 mg/L. Based on 1 g dosing, 5/6 patients with MRSA positive SSIs had wound closure levels of <15 mg/L and all six were <20 mg/L.
  
  
  CONCLUSIONS
  In settings such as hospitals, where the risk for resistant bacteria, especially MRSA, is high, it is becoming increasingly important to accurately dose patients who require vancomycin. In order to avoid incorrect dosing of vancomycin health care providers must use weight-based dosing.
authors.affiliation: NYU Hospital for Joint Diseases.
authors.forename: Anthony
authors.initials: A
authors.lastname: Catanzano
authors.affiliation: NYU Hospital for Joint Diseases.
authors.forename: Michael
authors.initials: M
authors.lastname: Phillips
authors.affiliation: NYU Hospital for Joint Diseases.
authors.forename: Yanina
authors.initials: Y
authors.lastname: Dubrovskaya
authors.affiliation: NYU Hospital for Joint Diseases.
authors.forename: Lorraine
authors.initials: L
authors.lastname: Hutzler
authors.affiliation: NYU Hospital for Joint Diseases.
authors.forename: Joseph
authors.initials: J
authors.lastname: Bosco
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000627:therapeutic use; D019072:Antibiotic Prophylaxis / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000009:adverse effects; D012189:Retrospective Studies; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000209:etiology / Q000517:prevention & control*; D013530:Surgical Wound Infection / Q000188:drug therapy / Q000209:etiology / Q000517:prevention & control*; D014640:Vancomycin / Q000008:administration & dosage* / Q000627:therapeutic use
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin
keywords: MRSA; spine surgery; surgical site infections; total joint surgery; vancomycin; weight based dosing