| Introduction. Increased mortality, treatment failure, and hospital lengths of stay have been reported in patients treated with vancomycin for MRSA bacteremia when their isolates have "high normal" MICs (>1). The ability to discriminate patients infected with these strains could allow decisions to consider alternative treatments.;Method. This cohort study was conducted at a tertiary care hospital and its affiliated acute rehabilitation facility. Patients with MRSA bacteremia were prospectively identified and data were collected during the period of 2001-2007. Factors were examined for their association with high vancomycin MIC and a predictive model was created.;Results. There were 295 MRSA bacteremic events among 271 patients that met inclusion criteria during the study period. Fifty-seven events (19%) had isolates that were found to have the outcome of high MIC (>1) to vancomycin. Variables found to be significantly associated with high vancomycin MIC in the univariate analysis included older age, prior vancomycin or daptomycin exposure, the presence of a non-tunneled central venous catheter or prosthetic heart valve, higher APACHE II score, a history of prior MRSA bacteremia, and the presence of sepsis or shock at the time of culture. A multivariable logistic regression model (c=0.74) was built and then candidate variables were chosen and assigned points based upon their coefficients in the model. Age>50 (3 points), prior vancomycin exposure (2 points), history of MRSA bacteremia (2 points), history of chronic liver disease (2 points), and presence of a non-tunneled central venous catheter (1 point) were included in the final model. The sum score of these points was determined for each bacteremic event and these scores performed with similar predictive ability to the original logistic regression model from which the point scores were derived (c=0.73).;Conclusion. Patients with elevated vancomycin MIC values may benefit from alternative therapy. There may be factors that can help predict which patients are likely to be infected with MRSA isolates that have elevated MICs to vancomycin. |
