Implementation of an antimicrobial stewardship pathway with daptomycin for optimal treatment of methicillin-resistant Staphylococcus aureus bacteremia

Abstract

Study objective: To evaluate a clinical pathway using daptomycin in patients with bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA) isolates exhibiting vancomycin minimum inhibitory concentrations (MICs) greater than 1 mg/L.

Design: Two-phase quasi-experimental study.

Setting: Level I trauma center in Detroit, Michigan.

Patients: The study population consisted of a total of 170 patients with MRSA bacteremia susceptible to vancomycin: 70 patients who had initial blood MRSA isolates exhibiting a vancomycin MIC > 1 mg/L and were treated with vancomycin were included in phase I (retrospective baseline period [2005-2007]) and 100 patients who were switched to daptomycin after initial vancomycin therapy according to the institutional MRSA bacteremia treatment pathway were included in phase II (the period after implementation of the treatment pathway [2008-2010]).

Intervention: The MRSA bacteremia treatment pathway was as follows: vancomycin therapy was initiated, optimizing target trough concentrations to 15-20 mg/L; for isolates demonstrating vancomycin MICs greater than 1 mg/L, therapy was switched to daptomycin, initiated at dosages of 6 mg/kg/day or higher.

Measurements and main results: Infection characteristics, patient outcomes, and costs were evaluated. Patient characteristics were similar between the phase I and phase II groups. Phase II patients were more likely to achieve clinical success than were phase I patients (75.0% vs 41.4%, p<0.001). Phase II patients demonstrated a shorter total hospital length of stay and shorter durations of inpatient therapy, fever, and bacteremia. Treatment during phase I was independently associated with failure. Nine patients during phase I experienced nephrotoxicity, and two patients during phase II experienced increases in creatine kinase level. Costs were similar between phases I and II ($18,385 vs $19,755, p>0.05), although the hospital readmission rate was higher in phase I (33% vs 21%, p=0.08).

Conclusion: Among the patients with bacteremia who had MRSA isolates that exhibited elevated vancomycin MICs, the switch to daptomycin improved clinical success without increasing treatment cost.