In this episode, I will:
- Review an article about monitoring vancomycin by trough levels
- Answer a drug information question: Why do some of my trauma patients get heparin and some enoxaparin for DVT prophylaxis?
- Share sleep hygiene resources that I personally use.
Author: John P. Prybylski
Published in Pharmacotherapy October 24, 2015
Can you believe vancomycin is over 50 years old and we still don’t know the best way to dose it?
Joint guidelines on dosing vancomycin were published by the Infectious Disease Society of America and the Association of Health Systems Pharmacists in 2009.
In these guidelines the authors recommend attaining a trough of 15-20 mg/L when treating serious infection due to Staphylococcus aureus.
This trough goal of 15-20 mg/L in serious infection was controversial when it came out in 2009 and remains so today.
This goal was proposed as a way to ensure that patients achieve the ideal 24-hour area under the concentration-time curve to minimum inhibitory concentration ratio (AUC:MIC) of at least 400 hours. However, analyses have demonstrated that patients with adequate renal function can typically achieve the AUC:MIC goal with a more conservative trough concentration.
To determine the strength of evidence for better clinical outcomes in patients with Staphylococcus aureus bacteremia who had vancomycin trough levels of 15–20 mg/L.
A meta-analysis of 14 observational cohort studies.
A total of 1677 patients who had vancomycin trough goals of 15–20 mg/L for the treatment of Staphylococcus aureus bacteremia were included in the meta-analysis. Trough levels of 15 mg/L or greater were not associated with significantly reduced treatment failure, persistent bacteremia, or mortality.
Higher AUC:MIC values were associated with significantly reduced treatment failure, persistent bacteremia, and mortality. The weighted mean standard deviation AUC:MIC threshold defined by regression analyses in the included studies was 418 +/- 88 hours, which supports the current goal of 400 hours or more.
This meta-analysis did not detect a benefit in treating complicated Staphylococcus aureus infections with a vancomycin trough goal of 15 mg/L or greater.
The author concluded that vancomycin trough concentrations do not have sufficient evidence to support their use as the primary guide in vancomycin dosing.
The author asserts that dosing should instead focus on AUC:MIC values, which have stronger evidence of benefit. He goes on to say:
Based on the results of this analysis, and the absence of randomized controlled trials to support any vancomycin trough concentration goal, clinical pharmacists should be cautious in relying on the trough parameter alone to assess appropriateness of vancomycin dosing, which should primarily optimize the AUC:MIC to a goal of at least 400 hours.
The results of this study should not be interpreted as an attempt to determine whether AUC:MIC-based dosing is preferred over trough concentration–based dosing because the design of the included studies did not accommodate such an analysis. The design of this study, as a result, should only be interpreted as hypothesis forming, and additional research is needed before a definitive conclusion can be reached. Future research should directly compare both dosing strategies prospectively in a homogeneous patient population using a single, objective, relevant end point, such as persistent bacteremia lasting longer than 7 days.
According to clinicaltrials.gov, there is one completed retrospective cohort study done in Taiwan looking at outcomes when dosing vancomycin by AUC:MIC vs trough concentration. Results have not yet been posted for this study even though the completion date was June 2014. I don’t speak Hokkien or Mandarin but I did email the lead author (Li-Jiuan (Rita) Shen) for this trial. She told me that the manuscript is under review and she is unable to say anything further.
I’m not sure how I will incorporate AUC:MIC monitoring into my practice with vancomycin. The formula to determine the AUC:MIC is complex and requires a peak and trough to be drawn at steady state.
I was able to find an article that proposed a simplified method to estimate the AUC:MIC. The method involves knowing the MIC from the laboratory, estimating creatinine clearance, vancomycin clearance and using that information to estimate the AUC:MIC.
I’ve created a calculator that replicates the methods from this study. For now, I’ll be using this estimate to help decide which end of the 15-20 mg/L trough range to aim for. If anyone listening has incorporated AUC:MIC monitoring into your current practice, I’d love to hear from you at firstname.lastname@example.org.
Drug information question
Q: I’m a new nurse in a surgical/trauma ICU and I was wondering why do some of my patients get subcutaneous heparin for DVT prophylaxis while others get subcutaneous enoxaparin? Is there a reason or is it physician preference?
A: It’s mostly due to physician preference.
The CHEST guidelines for major trauma patients give heparin, enoxaparin, or IPCDs a grade 2C recommendation. 2C = a weak recommendation based on low- or very-low-quality evidence, so this leaves a lot of room for physician preference.
Some reasons to choose enoxaparin are:
– Once daily dosing
– Less chance of heparin induced thrombocytopenia
Some reasons to choose heparin are:
– Ability to give twice daily instead of 3 times daily to straddle a high bleed risk / high clot risk situation
– Anesthesia won’t allow anything but heparin in a patient with an epidural
– Doesn’t require dose adjustment for renal failure
– Less expensive
Today I’m going to share a collection of 4 resources that I use in my personal life to help me get a good night sleep – and they don’t include a bottle of zolpidem!
I often use technology in the evening – usually to work on the podcast! When I’m done, I want to be able to fall asleep right away. The blue light from the computer screen suppresses melatonin production, which is necessary to fall asleep. I take several steps to block the blue light from reaching my eyes.
The first is a set of blue light blocking glasses that I picked up on amazon for under $13.
Next, I placed a free app on my computer and phone to help lower the intensity of the display and the amount of blue light emitted. The app I use on my mac computer is f.lux and the app I use on my android phone is twilight. I have both apps set up to reduce the amount of blue light emitted from the device starting at sunset. Unfortunately, f.lux and twilight are not available for the iPhone or iPad without jailbreaking the device.
I learned these tips and more in the book Sleep Smarter by Shawn Stevenson. This book takes sleep hygiene to the next level and is packed full of actionable ways to improve your sleep.
If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.