Outcomes and costs associated with a history of vancomycin exposure in patients with MRSA-related complicated bacteremia and infective endocarditis.

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is the primary cause of complicated bacteremia (CB) and infective endocarditis (IE). Studies have compared the costs of treatment with vancomycin to those of other agents, as well as the efficacy and tolerability of these treatments. However, a literature search found no published studies of the effects of vancomycin exposure on outcomes and hospital costs in patients with CB or IE due to MRSA.

OBJECTIVE: The aim of this study was to determine whether there is a quantitative relationship between the duration of vancomycin treatment or cumulative vancomycin exposure and outcomes or costs in patient with CB or IE due to MRSA.

METHODS: Electronic medical records of confirmed cases of MRSA-related CB or IE from July 1, 2006, to June 30, 2008, were retrospectively reviewed to identify patients with a history of vancomycin exposure or no vancomycin exposure. Those who received vancomycin were stratified by the amount of drug administered or the duration of treatment to determine the relationship between treatment and outcomes. Data collected included demographic information, treatment information, attributable mortality, MIC data, and hospital costs. Classification and regression tree analysis (CART) was used to determine whether a history of vancomycin exposure was associated with treatment failure, attributable mortality, or both. The Mann-Whitney U test and the Fisher exact test were used for univariate analyses, and logistic regression was used for multivariate modeling.

RESULTS: Data from 50 patients were evaluated (CB, 32; IE, 18). Overall rates of failure and attributable mortality were 32% and 16%, respectively. No significant differences were observed between the variables and costs. The CART break points for failure were ≥18.75 g and ≥14 days of vancomycin treatment in the previous 3 years; for attributable mortality, the CART break points were ≥45 g and ≥31 days. In the final multivariate model for failure, ≥18.75 g and ≥14 days of vancomycin treatment in the previous 3 years were predictors of failure (both, P = 0.002). Acute Physiology and Chronic Health Evaluation (APACHE) II score (P = 0.04), ≥45 g (P = 0.002), and ≥31 days of treatment (P = 0.002) in the previous 3 years were predictors of attributable mortality after adjustment for all covariates.

CONCLUSIONS: Using the present model, cumulative vancomycin amount and duration were associated with attributable mortality and clinical failure but not with costs.