Category Archives: Uncategorized

On the flip side

I give that a thumbs up!

Yesterday I shared a frustration, today, I’ll share one of those happy moments. We were bumming over the bad review, and have been for a few days, when what appears in one of our mailboxes? That’s right, some positive feedback, and a feature request! Woo-hoo!

Thank you for offering such a usable app. I hope you will continue developing others as clinically useful as RxCalc.

Thanks for that! It’s nice to hear something positive after getting a bad review.

Oh, what did he ask for? Glad you asked.

I seldom order peak levels anymore except in certain cases. As you know, most of the time we can do a very good job dosing and monitoring vanco patients with trough levels only. Because RxCalc requires both peak and trough levels in order to use the “Adjust with Levels” portion of the app, I am rarely able to use this feature. Is there any way to allow the peak level input to be optional?

Ahh, just you wait.

Vancomycin and nephrotoxicity in hospitalized patients

An article on the possible link between vancomycin trough concentrations and nephrotoxicity appears in a recent issue of Clinical Infectious Diseases (2009;49:507-14) . The article describes a retrospective study of 166 patients treated at Albany Medical Center Hospital in Albany, New York between January 2005 and December 2006. The study found that patients in the ICU, those with a weight of >/= 101 kg, and those with prolonged exposure to elevated vancomycin troughs (> 20mg/L) were associated with a greater risk for developing nephrotoxicity. The authors conclude that the vancomycin trough value was the parameter that best described this risk of toxicity. Based on this information, it appears that successful treatment of serious methicillin-resistant S.aureus infections with higher minimum inhibitory concentrations (MIC) may place patients at a greater risk for developing nephrotoxicity. The findings in the article are significant as recent guidelines recommend higher vancomycin trough concentrations for complicated S.aureus infections.
Although interesting and possibly informative, the information contained in the study is based on a small observational study in a single facility. The findings cannot necessarily be extrapolated to any significant degree to other patient populations and further studies are necessary to confirm the results on a larger scale. For now it appears that aggressive vancomycin therapy in addition to cautious monitoring of renal function and patient status is prudent when trough levels are approaching 20mg/L.

Why I wanted RxCalc

Cross-post from Jerry is our resident PharmD and co-creator of RxCalc.

I have a couple of passions when it comes to pharmacy. The first is a love of pharmacy technology. Very few pharmacists have an appreciation for the “operations” side of pharmacy which includes automated dispensing cabinets, automated carousels, automated TPN compounders, Pharmacy Information System, etc. These tools are absolutely necessary if we want to get pharmacists out of the physical pharmacy and at the bedside where they belong. My second passion is a little less known discipline known as pharmacokinetics. I have no idea why I like pharmacokinetics; I just do. Some kids like PB&J and some don’t. It’s just the way it is.

Vancomycin and aminoglycoside (especially vancomycin) pharmacokinetics are very popular in hospitals, and are part of a select group of drugs that physicians prefer pharmacists to handle. Doing pharmacokinetic consults isn’t difficult per se, but can involve lots of numbers and equations. Many people find it a bit tedious and boring. There is also considerable variability in methods used for performing pharmacokinetic calculations. For example there are several existing pharmacokinetic models for vancomycin including Bauer, Matzke, Winter, Moellering, etc. Some of the models are more popular than others, but each has merit. As I’ve heard many times, “there are many roads to Rome.”

Pharmacists typically choose a favorite pharmacokinetic model and then alter the model to fit their needs based on years of clinical experience. I’m no different. Even though I was taught pharmacokinetics by Mike Winter at the UCSF School of Pharmacy, I prefer the vancomycin formulas derived by someone else. Please don’t tell Mike, he’s considered one of the best in the business and might revoke my alumni card if he found out.

Not all pharmacokinetic “starts” and adjustments require advanced calculations. Often times, years of experience and a good eye are all you need. However, there are times when you need a little more. Since the days of the Palm Pilot, I’ve always desired a portable pharmacokinetics program. It always made sense to me to use the technology at my finger tips to make my job easier. I’ve written several pharmacokinetic calculators, including simple Microsoft Excel spreadsheets and a little Java Script tied to a web front end, but I never got the opportunity to create a portable version. The iPhone (and iPod Touch) changed all that. The iPhone is a compelling device with a great user interface and unheard of popularity among healthcare professionals. My desire for a portable pharmacokinetics calculator, and the appearance of the iPhone, resulted in the creation of RxCalc.

RxCalc is designed for pharmacists based on my experiences over the past ten years. While not perfect, RxCalc does what I need. It’s clearly a work in progress. I don’t use it all the time because it’s simply not necessary. I still do a lot of “guess work” here and there, but rely onRxCalc when I need something to handle the more advanced calculations. Like every piece of software ever used, there is room for improvement. I have received lots of good, constructive feedback from several users. Combined with my desires, the feedback has created quite a list of future “enhancements” I’d like to see in RxCalc over the next several months. Among these include High Dose Extended Interval (a.k.a. once-daily) aminoglycoside dosing, single dose vancomycin kinetics, the option to change units (i.e. lbs, kg, cm, inches, etc), the ability to select different dosing models, alternate color schemes or themes and a more user friendly interface. Unfortunately, I don’t have the skill set to make the changes myself. That’s why God gave me a brother. I come up with the ideas and he does all the work to make it a reality. We make a great team.

I mentioned in a previous post that it may be time for me to put away my calculator in favor of newer technology. Pharmacokinetics was the last thing I really needed my calculator for. Well, with the creation of RxCalc I’ve finally put my calculator in the drawer and have been using pen, paper and my iPod Touch almost exclusively for a few weeks now. I must say, so far the results have been encouraging.