Bugs 'n' Drugs: Vancomycin Dosing


"Hey, Daddy-O.  Are you hip to that newfangled antibiotic, vancomycin?  That stuff is Fat City for beta-lactamase-producing bacteria," said every 1950s physician everywhere.

Ah, a simpler time.  One could just give a patient 1 gram every 12 hours and they'd be riding on easy street.  Today we have some scary bugs and not enough antibiotics to cover them.  To further complicate things, we are struggling with the phenomenon of the vancomycin MIC creep - it means our vancomycin susceptibilities are worsening.  The worst thing our 1950s counterparts had to worry about was not letting "Rock 'n' Roll" poison America's youth.  It's too late for that, but it's not too late to optimize our vanco dosing strategies to help decrease resistance!  Hooray!

Vancomycin is a weird drug.  The pharmacokinetics and dynamics are a bit more complex than other medications.  For instance, it is neither fully a time-dependent antibiotic (beta-lactams), nor a fully concentration-dependent antibiotic (aminoglycosides).  Many different kinetic models have been proposed, but the general consensus is that it involves the ratio of the area under the drug concentration-versus-time curve and the MIC.  We call it the AUC/MIC ratio.

This simply means the trough level we obtain is a marker for an appropriate AUC/MIC ratio.  We know that we need to target a trough of 10 mg/L for a bug with an MIC <1.  The trough required for an MIC = 1 is around 15 mg/L.  As the MIC approaches 2 or more, we can no longer use vanco as a treatment option.  We are seeing MICs of 1 and 1.5 far more than we previously have.  Two ways of combating the vancomycin MIC creep is to do the standard antimicrobial stewardship (no more vanco x1 dose and d/c on oral antibiotics), and appropriately dose the drug.  

Due to the complex kinetics involved, there are a multitude of dosing strategies.  Each institution may do things differently based on practicality and accuracy of the pharmacy kinetic team.  However, each strategy is based off of two things: body weight and renal function.

Standard Method:

  • Most common dosing technique
  • Load 20-25 mg/kg (max. 2000 mg)
  • 15 mg/kg at various intervals (every 8, 12, 24, etc. hours) based on renal function

Our pharmacy uses the Rodvold Method with a couple twists.  This is based of off years of kinetic data and how our pharmacy team has done in regards to obtaining a target trough.  I won't bore you with the details, but just know we rarely do a loading dose and rarely dose at 8-hour intervals.

I'll cut to the chase.  1,000 mg of vanco is not a one-size fits all dose.  We have to be sure we are setting up these patients for success during their hospital course.  Here is my recommendation for when your friendly ER pharmacists are not around: 

  • To the right of the vanco order in our system, click on the grey box with the ellipsis in it.  Select "Vanco Rx to Dose."  The RN will then call down to the main pharmacy where our team will conjure up a dose using our vanco voodoo.
  • Dose it yourself. It's super fun! I recommend a 15-20 mg/kg one-time dose using actual body weight, rounded to the nearest 250mg.  We will take care of the dosing interval when it gets continued in-house.  

Bottom line:

  • Vanco dosing is patient-specific
  • 15-20 mg/kg one-time dose with a max of 2 grams, or
  • Utilize "pharmacy to dose" function
  • Under-dosing vanco will increase the time required to get to a therapeutic trough
  • One gram q12h for everyone is not recommended