Daptomycin For Intravenous Access-Related MRSA Septicemia: A Case Report

摘要

A 32-year-old black man receiving hemodialysis presented with intravenous access-related methicillin-resistant Staphylococcus aureus (possibly heterogenous vancomycin-intermediate S. aureus). He was successfully treated with daptomycin (minimum inhibitory concentration = 2 μg/mL) in spite of data from three laboratories suggesting the isolates were not susceptible to daptomycin. Introduction Dialysis patients have a 100-fold higher risk for invasive methicillin-resistant Staphylococcus aureus (MRSA) infections than the general population [1]. Resistant vancomycin-intermediate S. aureus (VISA) and heterogenous (h)VISA have been shown to be selected for by vancomycin exposure in patients with significant underlying illness, particularly chronic renal failure [2]. This case illustrates the limitations of current laboratory antibiotic susceptibility testing for MRSA with regard to the choice of effective therapy (figure). Case Presentation The patient, a 32-year-old black male, was admitted to our hospital August 13, 2008, with confusion, fever, and swelling of the upper right extremity. Septicemia from a right subclavian hemodialysis catheter was suspected. He had had the catheter since May 2008 and was on hemodialysis 3 times per week. Since July 2007, he had had recurrent vancomycin-susceptible S. aureus bacteremia and vascular access infections. His medical history included longstanding type 1 diabetes mellitus, a left below-the-knee amputation due to peripheral vascular disease, renal failure, hepatitis C, and AIDS (CD4 = 186 cells/μL). He had refused highly active antiretroviral therapy. In March 2008, he had had a subtotal gastrectomy due to a bleeding peptic ulcer.An ultrasound of the right upper extremity showed a deep venous thrombosis of the subclavian, axillary, and cephalic veins. Blood cultures from the hospital laboratory on August 13, 2008, grew a vancomycin-susceptible MRSA with a vancomycin minimum inhibitory concentration (MIC) of 2 μg/mL. He was started on vancomycin on August 13 at doses between 0.75 g and 1 g on hemodialysis. The subclavian catheter was removed on August 15, 2008, and replaced with a right femoral catheter. Cultures of the catheter tip and venipuncture blood cultures done the same day grew MRSA susceptible to vancomycin and linezolid, both with an MIC = 2 μg/mL. Daptomycin was not tested. He had received the 2 doses of vancomycin before repeat blood cultures (1 from venipuncture and 1 from the new femoral catheter) were obtained on August 20, 2008, which remained positive for MRSA. The local lab (Willis Knighton) referred the cultures to a reference lab (Focus) and the Centers for Disease Control (CDC) for daptomycin susceptibility testing. The results are given in table 1. He also received gentamicin at a dose of 80 mg on August 20 and 22, on hemodialysis. On August 20, 2008, while still on vancomycin, the patient was started on daptomycin at a dose of 6 mg/kg every 48 hours. On August 25, 2008, when the first daptomycin susceptibility results became available, the daptomycin MIC was 2 ug/mL, defined as non-susceptible, so linezolid was added to daptomycin. However, blood cultures from August 21 and 23, 2008, were both negative after 1 day of treatment with daptomycin and before the addition of linezolid. The patient was discharged from the hospital on September 3, 2008, and continued on both daptomycin and linezolid given after dialysis. He was readmitted to the hospital on September 8, 2008, with thrombocytopenia attributed to linezolid, which was discontinued. He remained on daptomycin as an inpatient on dialysis from September 10, 2008, through September 21, 2008. Figure. Summary of the treatment course and vancomycin and daptomycin minimum inhibitory concentrations (MICs) for methicillin-resistant Streptococcus aureus (MRSA) bloodstream and/or catheter tip isolates. +RFC, right femoral catheter inserted; -SCC, infected subclavian catheter removed, TCP, thrombocytopenia develops. Note: f