We’re working on the next release of RxCalc and would like to open it up to some beta testers! If you’re interested please fill out the RxCalc Beta Program form and we’ll consider you for the program. It’s that easy.
Thanks for supporting RxCalc, and helping us to make 1.2 the best release ever.
Something we need to do here at Apple Core Labs is create a FAQ for RxCalc. I’ve been saying that for quite a while now but I just haven’t gotten around to it. It’s one of those things that falls to the bottom of the list, but it really is time I did it.
We need to get this hammered out so we avoid bad reviews to be quite honest. Our calculations are accurate but we continue to receive reviews that say otherwise. There is no one true method for deriving Pharmacokinetics calculations. There are many methods. To say RxCalc under doses is true, and false, all at the same time. If you’re a new Pharmacist, or married to a particular method, you may be extremely disappointed with the numbers RxCalc produces.
By creating a FAQ the hope is we’ll help remove that disappointment. RxCalc currently uses the following Creighton formulas for vancomycin calculations:
- Cockcroft and Gault equation using IBW for creatinine clearance (use ABW if less than IBW)
- Elimination rate constant: ke = (0.00083 * CrCl) + 0.0044
- RxCalc considers the total dose of vancomcyin per dosing interval determined by equation; in this case [(ln Cp-ln Ctr)/ke] for the interval and [Cp*Vd*(1-e-^(ke*tau))] for the dose.
- Vd is defaulted to 0.7 liters/kg, but can be changed to the users taste between 0.5-1 liter/kg
Vancomycin dosing is so variable, and there are so many methods, that it was difficult to chose just one. Methods for vancomycin kinetics include Bauer, Burton, Matzke, Moellering and Winter just to name a few. At the time RxCalc was designed the Apple Core Labs team felt most comfortable with the formulas dervied by Creighton. This choice was neither right nor wrong as vancomycin kinetics are as much an art form as they are a science. You will find many different methods used throughout the various schools of pharmacy and medical centers in the United States.
With that said, Apple Core Labs chose to offer an adjustable volume of distribution for RxCalc, in effect giving the end user an amount of flexibility in their calculations. The option to set your default volume of distribution from 0.5 liters/kg to 1.0 liters/kg can make a significant difference in the final outcome of your vancomycin calculations. RxCalc relies not only on numbers to perform calculations, but the end user’s clinical acumen and experience as well.
Apple Core Labs will continue to improve RxCalc by adding features and improving functionality. We appreciate any and all feedback, no matter how good or bad. One thing we would like to request from our end users is detailed information included with their comments. If we know what method the user is comparing the results generated by RxCalc to, we can better understand what the problem might be and how best to help.
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.
I believe it was Marco Arment that gave the advice “Don’t read App Store Reviews”, or something to that effect, and I can see why. For RxCalc they’ve typically been fairly poor. Some have provided great feedback that lead to changes in the applications, but recently we received a review that left us scratching our heads. Here’s the review.
This program really underdoses all my patients. It predicts troughs of 20 and 25 with normal doses. I used it just the other day and it predicted a trough of 26.4 and I got an actual trough of 14.7–no changes clinically with the patient. This program is crap. Good thing it only cost 99 cents!
Can you see the problem facing an app developer with a review like that? Actually there are many problems with it. Here are the two biggest, as I see it.
- It doesn’t provide any meaningful feedback – We can’t reproduce the “problem” or fix it.
- We have no way to contact the user to see if we can help.
I really wish this user would’ve contacted us via our support e-mail address. We’re very confident our math is correct, we spend a lot of time verifying the results, it’s what makes the application useful. I’d venture to guess this is a configuration issue, but alas, we’ll never know.
We’re grateful for our users and we want to make their experience the best they’ve ever had. RxCalc should help you do your job, not hinder it. We like the feedback, good or bad, and love when it leads to improvements in the overall usability, and performance, of the application.
It’s disappointing when we see a review in the App Store like this because we can’t help this user solve their problem.