UMEM Educational Pearls

Title: Vancomycin Loading in Obese Patients

Category: Pharmacology & Therapeutics

Keywords: obese, vancomycin, loading dose (PubMed Search)

Posted: 5/22/2015 by Bryan Hayes, PharmD (Updated: 6/6/2015)
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Vancomycin guidelines recommend an initial dose of 15-20 mg/kg based on actual body weight (25-30 mg/kg in critically ill patients). [1] The MRSA guidelines further recommend a max dose of 2 gm. [2]

But, what dose do you give for an obese patient that would require more than 2 gm?

A new study provides some answers to this question. [3] Obese-specific, divided-load dosing achieved trough concentrations of 10 to 20 g/mL for 89% of obese patients within 12 hours of initial dosing and 97% of obese patients within 24 hours of initial dosing.

Application to Clinical Practice

Calculate the total loading dose. At my institution we use actual body weight (the study used IBW).
Divide the total dose to be given every 6 hours until load is complete. We cap each individual dose at 2 gm (the study used 1.5 gm).
Measure a trough level before the third dose.
Change to dosing frequency dictated by renal function once level moves into target range.

Caveats

The study used some more specific dosing calculations based on renal function and percentage above IBW. If patient's renal function is abnormal, consultation with a pharmacist is recommended.

References

Ryback M, et al. Therapeutic monitoring of vancomycin in adult patients: a consensus review of the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Diseases Pharmacists. Am J Health Syst Pharm 2009;66(1):82-98. [PMID 19106348]
Liu C, et al. Clinical practice guidelines by the Infectious Diseases Society of America for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children: executive summary. Clin Infect Dis 2011;52(3):285-92. [PMID 21217178]
Denetclaw TH, et al. Performance of a divided-load vancomycin dosing strategy for obese patients. Ann Pharmacother. 2015 May 18. [Epub ahead of print, PMID 2598600]

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