Monthly Archives: May 2010

Introducing RxCalc 1.1

Pharmacokinetics, Pharmacy, RxCalc

RxCalc 1.1When we released RxCalc 1.0 we felt the need to focus most of our effort on making sure our math was correct. We felt if the standard user interface was good enough for Apple, it was good enough for us. Since that time we’ve collected a bit of feedback, some great, some not so great, and a couple of really horrible comments that made us cringe. Fear not! We picked ourselves up off the ground, regrouped, and went to work on RxCalc 1.1. We hope you enjoy using it as much as we enjoyed developing it.

What’s New in 1.1?

Options

  • User configurable Units of Measure
    1. Height
    2. Weight
    3. Serum Creatnine
  • Configurable Volume of Distribution
    1. Aminoglycoside
    2. Vancomycin
  • Less rigid scrolling
  • Less rigid data entry

The big addition is the user configurable Units of Measure and adjustable Volume of Distribution. These should help folks outside the United States and gives flexibility to those that would like to modify the default Volume of Distribution values. We’re also really happy with the new navigation experience. Version 1.0 was a bit rigid, we’ve changed that. You can now freely move between entry fields and scroll top to bottom with complete freedom, while the keyboard is showing.

Oh, yeah, it also has a great new icon! Courtesy of our good friend, Mr. Layne Lev.

Cockcroft-Gault equation remains an effective way to estimate GFR

aminoglycosides, Pharmacokinetics, ,

From The Annals of Pharmacotherapy Vol. 44, No. 6, pp. 1030-1037:

Evaluation of Aminoglycoside Clearance Using the Modification of Diet in Renal Disease Equation Versus the Cockcroft-Gault Equation as a Marker of Glomerular Filtration Rate

BACKGROUND: Accurate estimation of kidney function is essential for safe administration of renally cleared drugs. Current practice recommends adjusting renally eliminated drugs according to the Cockcroft-Gault (CG) equation as an estimation of glomerular filtration rate. Few data exist regarding the utility of the Modification of Diet in Renal Disease (MDRD) equation in drug dosing.

OBJECTIVE: To evaluate glomerular filtration rate based on creatinine clearance (CrCl) derived from the MDRD or the CG equation compared with patient-specific CrCl calculated from aminoglycoside peak and trough concentrations.

METHODS: Medical records of patients who received aminoglycoside antibiotics were reviewed over 1 year. Patients who received aminoglycosides via conventional dosing with peak and trough concentrations at steady state were included. Calculations based on standard pharmacokinetic equations were used to estimate CrCl from aminoglycoside serum concentrations. Patient-specific CrCl estimated from aminoglycoside concentrations was compared with estimated CrCl from the CG or MDRD equation.

RESULTS: Fifty-five patients were included in the final analysis. The primary outcome showed concordance between estimated and actual aminoglycoside clearance was 0.53 (95% CI 0.18 to 0.88) for the CG equation and 0.41 (95% CI 0.04 to 0.78) for the MDRD equation. Subgroup analysis also favored CG as a better predictor of CrCl. This signified a stronger correlation between the CG equation and aminoglycoside clearance.

CONCLUSIONS: Compared with the MDRD equation, the CG equation provided better correlation of estimated glomerular filtration rate for aminoglycoside antibiotics. Institutions should continue to use the CG equation as the standard of practice to safely adjust aminoglycoside doses in patients with renal dysfunction.

It appears that the Cockcroft-Gault (CG) equation remains an effective way to estimate GFR for aminoglycoside PK calculations. I’ve been using the CG equation since my pharmacy school days and have no immediate plans to make a change.

The Good, The Bad, and The Ugly

App Store, RxCalc,

When we released RxCalc we did what most companies do, we setup a page for the application and made sure we listed various different contact addresses on the page as well as creating a contacts page. We had hoped we’d get feature requests, support requests, and constructive criticism. What we’ve discovered is our users don’t really provide much feedback. We’ve had some, but not a lot. We have, however, had a few folks give feedback on iTunes. Some great, some not so great. It’s been a strange ride and I thought I’d share some of that feedback here.

The Good

“I’ve been using this app for a week or so, comparing results to a program I’ve used on my Palm for several years. The two calculate very similar results, and I find myself using RxCalc more and more.”

This user actually sent us a direct e-mail with a feature request. He was interested in better options, like being able to enter height in centimeters and being able to adjust the Volume of Distribution value. Just the kind of feedback you hope for, and he asked for something that would make his experience better. Great stuff.

The Bad

“The interface is rigid and clunky…”

Rigid and clunky, ouch. This feedback has actually been quite helpful. We’ve made changes to an upcoming release to address this very problem. We’re hopeful this user will be happy with the change, if he’s still using RxCalc. If he’s not, we hope he gives it another try.

The Ugly

“Does not work. Interface is clunky and gives me error messages when I put in values. I don’t believe for a minute the positive reviews are real. Cannot use product nor would you want to trust calculations (if you can get them from the app!) in a clinical setting. If it smells like garbage, works like garbage, and looks like garbage, it probably is.”

This review just makes us cringe. We know exactly what this user is talking about. The UI in 1.0 is rigid, we thought it was a good thing but it turns out that wasn’t such a great idea. In trying to protect the user we made some mistakes. Those have been addressed in the next release.

For our 1.0 release we focused heavily on the math and tried to keep the UI as simple as possible. Most of the feedback we’ve received has been UI related and we’ve concentrated on those issues. The math has been solid and is something we haven’t taken lightly.

What can you expect?

I think it’s safe to say we’ve addressed these issues in the next release. We hope our users are happy with the changes, and we think you will be.