In this episode, I’ll discuss a recent article about vancomycin monitoring.
Shout out to “Pharmacy David,” “Pharmacy Lisa,” and “Pharmacy Kathryn” at the Department of Pharmacy Practice & Science, University of Arizona for inspiring this episode!
I can’t remember ever being as excited about a journal article as I am over one that was recently published in AJHP that has to do with a new way to look at vancomycin monitoring.
As I discussed back in episode 523, the latest vancomycin guidelines now recommend AUC/MIC based monitoring over traditional trough-only monitoring.
When using a trough range of 15-20 mg/L, one is essentially guaranteed of achieving the ideal AUC/MIC for efficacy of >400. This is because a trough of 15 mg/L represents a 24-hour AUC of 360, and since the peak level is much higher than 15 mg/L, the additional area under the concentration curve will always add up to above 400.
The trouble with this method is that although it guarantees meeting the AUC/MIC target of 400, the AUC/MIC value may be well in excess of 400. This means that additional toxicity risk is undertaken when using the convenience of dosing by trough value instead of AUC/MIC.
This change was made in 2020 because the guideline authors opinion is that the trade-off of monitoring simplicity vs toxicity that trough values represent is no longer justifiable given the knowledge and technology available to clinicians today.
While many hospitals have had difficulty with the implementation of AUC/MIC based monitoring, the authors of this recent article in AJHP have proposed an elegant solution that should satisfy the need for simplicity of monitoring with the need for AUC/MIC based targets.
The authors propose determining a patient’s specific kinetics with two vancomycin levels just once, and then using that data to calculate a patient-specific trough range that will correspond to an AUC/MIC of 400 to 600. Going forward, the patient-specific trough range can be used to monitor and adjust the patient’s vancomycin dosing.
Here is how this model would work in practice:
Step 1: Give your usual vancomycin loading dose.
Step 2: Start maintenance dosing based on population estimates to achieve the desired AUC/MIC.
Step 3: Check 2 serum concentrations during 1 dosing interval (this could be after the 1st, before steady-state, or once at steady-state depending on how you do your pharmacokinetic analysis in the next step).
Step 4: Use pharmacokinetic analysis to determine patient-specific kinetic values.
Step 5: Use the patient-specific kinetics value to tweak the current dosing regimen.
Step 6: Use the patient-specific factors to calculate a unique trough range that will correspond to an AUC/MIC of 400-600.
This technique seems to strike an ideal balance between the old practice of trough-only monitoring and the desired new practice of AUC/MIC based monitoring. And while it doesn’t solve the age-old problems of kidney function fluctuation, troughs drawn too early or missed/held doses, it does seem to point the way forward for a more simplistic and practical application of the vancomycin guideline authors’ wish to use AUC/MIC based dosing to reduce unnecessary vancomycin toxicity.
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Joe, does your facility use AUC dosing? We’re still doing troughs only. If you do, how do you navigate changing renal function in your practice?
Hi Kelsey, unfortunately, we are still stuck using trough-based dosing for the time being due to administrative issues even though many of us would prefer to make the switch.