Session:

Antibiotics

Abstract No.:

56.032

Title:

Possible antagonism with use of ceftaroline and rifampin to treat methicillin-resistant Staphylococcus aureus infection

Author(s):

V. Sundareshan1, J. Modi2, S. Bergman3, J. Koirala1; 1Southern Illinois University School of Medicine, Department of Medicine, Division of Infectous Diseases, Springfield, IL/US, 2SIU school of medicine, Infectious Diseases, Springfield, IL/US, 3Southern Illinois University School of Pharmacy, Edwardsville, IL/US

Abstract:

Background: A 57 year old male was seen in the hospital for right shoulder septic arthritic with methicillin resistantStaphylococcus aureus(MRSA). He was treated with arthroscopic debridement and intravenous vancomycin until susceptibilities were available. The minimum inhibitory concentration (MIC) for vancomycin was 1.5 mcg/ml, therefore the patient was discharged home on 6mg/kg of daptomycin once daily to be given for 4 weeks. The MIC of daptomycin was not checked at that time. Patient returned for follow up in 3 weeks and complained of persistent fever and low back pain. Blood cultures were drawn that grew MRSA again. Spinal imaging revealed lumbar diskiitis.  We present here a case where ceftaroline was used for treatment along with rifampin to treat a highly resistant strain of MRSA and the results of our laboratory tests.
Methods: Laboratory tests performed on the isolate of MRSA from blood cultures revealed a high MIC of daptomycin that was in the resistant range. There was now also a creep noted in the MIC of vancomycin. The patient’s therapy was changed to ceftaroline which resulted in negative blood cultures within 24 hours of initiating therapy. Serum inhibitory concentration (SIC) and serum bactericidal concentration (SBC) were performed using the patient’s serum prior to a dose of ceftaroline after steady state (trough). Rifampin was added to therapy after reviewing the results as shown below in table 1. The SIC and SBC were repeated when he was treated with a combination of ceftaroline and rifampin.
Results:

Table - 1
                     MIC using E- tests(mcg/ml) SIC                   SBC                      
 Vancomycin 2.0Not indicatedNot indicated
 Daptomycin 3.0Not indicatedNot indicated
 Ceftaroline 0.381:8 dilution1:16 dilution
 Ceftaroline and rifampin --1:16 dilution Not achieved

Conclusion: Even with the availability of newer antibiotics in the United States with activity against MRSA, treatment of MRSA infections (particularly bloodstream infections) can be suboptimal. Frequent laboratory testing with SIC and SBC may be necessary even in the absence of negative blood cultures as a preemptive measure to detect impending clinical failure. The SIC and SBC results with the combination of ceftaroline and rifampin suggest antagonism between the two antibiotics. Further laboratory tests are necessary to establish that. This patient was successfully treated with quinupristin/dalfopristin for 6 weeks.
   


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