Don't Switch From Vancomycin for MRSA Bacteremia Just for an MIC of 2 mg/L

We're getting 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 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 your ID specialist...and don't be surprised to see med 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.

See our chart, MRSA Bacteremia in Adults: FAQs, for more on dosing, other salvage options, PO switches, and linezolid's role.

Key References

  • Antimicrob Agents Chemother 2019;63(5):1-10
  • Clin Infect Dis 2011;52(3):e18-55
  • J Clin Pharm Ther 2018;43(5):614-25
  • JAMA 2014;312(15):1552-64
  • Medication pricing by Elsevier, accessed Jun 2019
Hospital Prescriber's Letter. July 2019, No. 350719

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