Effectiveness of Daptomycin in Patients with Persistent Methicillin-Resistant Staphylococcus aureus Bacteremia Despite Vancomycin

Clinicians often switch therapy in patients with persistent methicillin-resistant Staphylococcus aureus(MRSA) bacteremia despite prolonged vancomycin therapy. We evaluated the utilization of daptomycin in MRSA bacteremic patients who failed vancomycin therapy. This single center, retrospective evaluation of adult patients who received daptomycin after receiving vancomycin for MRSA bacteremia from January 2011 to September 2016. Persistent bacteremia was defined as continued positive blood culture(s) despite receiving more than 72 hours of vancomycin. Patients with bacteremia from presumed pneumonia or MRSA bacteremia within 30 days of admission were excluded. Daptomycin dose was evaluated for appropriateness based upon patient weight and renal function. Duration of bacteremia was evaluated, including whether source control was achieved. Creatinine phosphokinase (CPK) levels drawn during daptomycin therapy were assessed to evaluate safety. Hospital length of stay and patient disposition were collected for each patient. Data were presented with descriptive statistics. 700 patient received daptomycin during this study period; 66 were duplicates, 596 did not meet inclusion criteria and 38 patients were included. Minimum inhibitory concentrations (MICs) of isolates were 1mcg/mL (31.6%), 1.5mcg/mL (42.1%) and 2mcg/mL (26.3%). Daptomycin dose was 4mg/kg (10.5%), 6mg/kg (63%), 8mg/kg (16%) and 10mg/kg (10.5%). Twenty-eight (73.7%) of 38 patients cleared bacteremia with daptomycin. Ten patients were switched back to vancomycin for the following reasons: persistent bacteremia (6), increase in daptomycin MIC (3), and blood culture was negative on the date daptomycin was initiated (1). Duration of bacteremia while receiving vancomycin vs. daptomycin was 8.5 ± 6.6 days and 4.9 ± 5.4 days, respectively. Only one patient experienced elevated CPK > 5 times upper normal limit. Daptomycin was utilized appropriately in 97.4 % of the patients who failed vancomycin according to our current protocol. Daptomycin was effective in a majority of the patients in clearing bacteremia but MICs increased in some patients. Prospective studies should be performed to confirm these findings. All authors: No reported disclosures.