As a hospital pharmacist, you will ask yourself questions about the optimal treatment for methicillin-resistant Staph aureus (MRSA) bacteremia in adults. Consider these strategies when treating your patients...
Continue to use vancomycin first. Daptomycin is also first-line, but there's no good evidence it works better, and it costs more. Rule out endocarditis with an echocardiogram. And eliminate the MRSA source, such as an infected IV catheter or undrained abscess. After starting vancomycin, generally recheck blood cultures about every 2 days until clear. When determining treatment duration, consider the first negative blood culture to be day one, NOT the first day of antibiotics.
Treat uncomplicated bacteremia for at least 2 weeks. These are patients with negative cultures and fever resolution within about 3 days of starting treatment, PLUS no implanted devices or deep-seated infections, such as endocarditis or a pulmonary abscess. Consider everyone else complicated and treat for at least 4 weeks.
Think about daptomycin if vancomycin fails. For example, switch if cultures are still positive after about 5 to 7 days of vancomycin. Consider an earlier switch to daptomycin for patients who are getting worse or when repeat cultures are positive PLUS the vancomycin minimum inhibitory concentration (MIC) is 2 mg/L. But don't switch just for a vancomycin MIC reported as 2 mg/L. This is the upper limit of the susceptibility range. But lab-reported MICs can be imprecise. Plus using vancomycin when the MIC is 2 mg/L doesn't seem to be linked to increased mortality. Generally use higher daptomycin doses; 8 to 10 mg/kg/day and adjusted body weight when body mass index is 30 kg/m2 or more.
Use salvage therapy for vancomycin and daptomycin failure. Work with infectious disease specialist and don't be surprised to see medication combos. For example, the fifth-generation cephalosporin ceftaroline (Teflaro) covers MRSA and seems synergistic when added to daptomycin. But consider scheduling ceftaroline Q8 hours instead of Q12 hours.
REFERENCES
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Geriak M, Haddad F, Rizvi K, Rose W, Kullar R, LaPlante K, Yu M, Vasina L, Ouellette K, Zervos M, Nizet V, Sakoulas G. Clinical Data on Daptomycin plus Ceftaroline versus Standard of Care Monotherapy in the Treatment of Methicillin-Resistant Staphylococcus aureus Bacteremia. Antimicrob Agents Chemother. 2019 Apr 25;63(5):e02483-18. Available at: https://journals.asm.org/doi/10.1128/AAC.02483-18?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed
Liu C, Bayer A, Cosgrove SE, Daum RS, Fridkin SK, Gorwitz RJ, Kaplan SL, Karchmer AW, Levine DP, Murray BE, J Rybak M, Talan DA, Chambers HF; Infectious Diseases Society of America. Clinical practice guidelines by the infectious diseases society of america for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children. Clin Infect Dis. 2011 Feb 1;52(3):e18-55. Available at: https://academic.oup.com/cid/article/52/3/e18/306145
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Kalil AC, Van Schooneveld TC, Fey PD, Rupp ME. Association between vancomycin minimum inhibitory concentration and mortality among patients with Staphylococcus aureus bloodstream infections: a systematic review and meta-analysis. JAMA. 2014 Oct 15;312(15):1552-64. Available at: https://jamanetwork.com/journals/jama/fullarticle/1913620