JAC Advance Access published online on August 11, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn329
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Original research |
Predictors of high vancomycin MIC values among patients with methicillin-resistant Staphylococcus aureus bacteraemia
1 Albany College of Pharmacy, Department of Pharmacy Practice, Albany, NY, USA 2 Ordway Research Institute, Albany, NY, USA 3 Albany Medical College, Division of HIV Medicine, Albany, NY, USA 4 Albany Medical Center Hospital, Department of Pathology and Laboratory Medicine, Albany, NY, USA 5 Albany Medical Center Hospital, Department of Epidemiology, Albany, NY, USA
Received 23 June 2008; returned 14 July 2008; revised 21 July 2008; accepted 22 July 2008
* Correspondence address. Albany College of Pharmacy, Department of Pharmacy Practice, 106 New Scotland Avenue, Albany, NY 12208-3492, USA. Tel: +1-518-445-7292; Fax: +1-518-694-7062; E-mail: lodiset{at}acp.edu
Background: Recent evidence suggests that vancomycin demonstrates reduced activity against methicillin-resistant Staphylococcus aureus (MRSA) infections when vancomycin MIC values are at the high end of the susceptibility range (
1.5 mg/L). However, scant research exists on factors predictive of high vancomycin MICs (1.5 mg/L) among MRSA bacteraemic patients. Empirical therapy decisions would greatly benefit from such information.
Objectives: To identify the parameters predictive of high vancomycin MICs (1.5 mg/L) among MRSA bacteraemic patients and to develop an evidence-based clinical prediction tool.
Methods: This observational cohort study included adult patients with MRSA bloodstream infections between January 2005 and May 2007. Demographics, co-morbid conditions, and microbiology and antibiotic exposure data were collected. Vancomycin MICs were determined by Etest. Stepwise logistic regression was used to identify independent predictors of high vancomycin MICs.
Results: Of the 105 patients who met the inclusion criteria, 77 patients (73.3%) exhibited a high vancomycin MIC (1.5 mg/L). In the bivariate analysis, prior vancomycin exposure within 30 days of index culture collection [15 patients (19.5%) versus 1 patient (3.6%), P = 0.05] and residence in an intensive care unit (ICU) at the onset of infection [27 patients (35.1%) versus 3 patients (10.7%), P = 0.02] were both significantly associated with a high vancomycin MIC value and both were independent predictors of high MICs in the logistic regression.
Conclusions: Patients with MRSA bloodstream infections in the ICU or with a history of vancomycin exposure should be considered at high risk of infection with strains for which vancomycin MICs are elevated. Appropriate and aggressive empirical therapy is required for these patients.
Key Words: susceptibility , epidemiology , outcomes , MRSA