As I reviewed my ID notes from what felt like an eternity ago, I wondered "Why can't oral Vancomycin be used to treat systemic infections?"

I found the answer in my notes, but I knew quoting my 3-year-old ID notes on rounds wouldn't fly!

#UKAPPE

1/13

So, let's pretend you're the staffing pharmacist and you see an order for PO vancomycin in the queue.

What do you think the patient's diagnosis in the chart is for?

2/13

Wellllll, it turns out your patient DOES NOT have C diff. They have been diagnosed with endocarditis.

After changing the order to IV vancomycin, you still wonder, "Why can’t we use oral vancomycin for susceptible systemic infections?"

3/13

Before I tell you the answer, let's go over some basic Vancomycin pearls!

- It is a tricyclic glycopeptide antibiotic
- It is bactericidal

4/13

https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/060180s047lbl.pdf

Vancomycin inhibits bacterial cell wall synthesis by blocking glycopeptide polymerization through binding tightly to D – alanyl – D – alanine portion of the cell wall precursor

5/13

https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/060180s047lbl.pdf

Vancomycin is a time-dependent killer; meaning it needs to be at the site of action for longer periods of time.

The 24-hour AUC/MIC needs to be ~400 to reach target levels.

To achieve this, it needs to have good bioavailability.

6/13

https://www.researchgate.net/figure/Pharmacokinetic-and-pharmacodynamic-parameters-AUC-area-under-the-curve-AUC-MIC-ratio_fig3_260120602

The reason we can't use oral Vancomycin for systemic infections is because of KINETICS!

Before we move on, here are 2 infographics to refresh your memory!

7/13

https://www.cyprotex.com/admeguide/introduction/adme-and-pk

Oral Vancomycin has poor oral bioavailability, which means only a small amount of medication enters the circulation.

We can't use oral Vancomycin for systemic infections because it doesn't reach therapeutic concentrations!

8/13

https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/060180s047lbl.pdf

So why can't we just use IV Vancomycin to treat C Diff?

9/13

Instead of absorption being the Achilles heel, it’s the distribution!

IV Vancomycin has a low Vd and because of this, it doesn’t achieve appropriate concentrations in the colon that are needed to treat C Diff!

10/13

There can be exceptions in PK in some cases. PO Vancomycin is an example of this!

There are RARE cases that have shown systemic concentrations of vancomycin because of changes in elimination and absorption.

11/13

There has also been a case study done with a patient who had normal renal function but had gastrointestinal inflammation that led to increased absorption and detectable serum levels.

12/13

https://ovidsp-dc2-ovid-com.ezproxy.uky.edu/sp-4.06.0a/ovidweb.cgi?&S=FABLFPECMBEBHBMNIPBKNHEHLBBEAA00&Complete+Reference=S.sh.27%7c1%7c1&Counter5=FTV_complete%7c00007611-200605000-00019%7covft%7covftdb%7covfth

As a student, PK was my arch-nemesis! And as much as I hate to admit it, PK is an important concept to determine the most effective medication regimens for our patients.

Vancomycin is just one of MANY examples of why knowing the implications of PK parameters matters!

13/13

I would like to thank @DrJeffCain & @AdrienneMatson for allowing me to do this tweetorial and for their guidance!

A big thank you to the pharmacists who reviewed this for me as well!

So thankful for the opportunities that @UK_COP has brought to me!!

#UKAPPE