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The Official Weblog of Apple Core Labs

Happy Birthday!

July 4th, 2010

Rob Fahrni

Not only are we celebrating the birth of our Great Nation, we’re also celebrating the first birthday of RxCalc!

One year ago today Jerry and I checked the store to discover our baby has bee accepted on Independence Day.

What a great day to be accepted!

Happy birthday United States of America! Happy birthday RxCalc!

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June 25th, 2010

Rob Fahrni

Be the first to press our stylish Facebook Like button at the bottom of our posts!

Introducing RxCalc 1.1

May 28th, 2010

Rob Fahrni

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

May 21st, 2010

Jerry Fahrni

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

May 19th, 2010

Rob Fahrni

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.

Become a Fan!

February 28th, 2010

Rob Fahrni

Not only do we have a Twitter page, we now have a Facebook page. Head on over and become a fan! We’d love for you to share your stories or post a picture.

Let’s have some fun!

Relief for Haiti, update

January 21st, 2010

Rob Fahrni

Aid!Good morning! It looks like yesterday’s Indie+Relief effort was a huge success! Even though we blew it and didn’t get in on the official program we decided to do what we could. We’re sending $50.00 to Doctors without Borders in the name of our users. We’d like to extend our whole hearted thanks to everyone that participated in the various efforts around the Mac Indie scene yesterday.

We’re very small, and the dollar amount we’re sending seems small, but every little bit helps.

THANK YOU!

Relief for Haiti

January 19th, 2010

Rob Fahrni

The Mac and iPhone Indie community have put together a relief effort for Haiti called Indie+Relief, brought to you by Second Gear Software and Garrett Murray. Apple Core Labs tried to participate but we were just too late due to an overwhelming response, and our lateness to join the effort. Fear not! We’re going to join the effort, just not through Indie Relief.

What does that mean?

Quite simply this. Apple Core Labs will donate all proceeds from sales of RxCalc on January 20, 2010 to Doctors Without Borders to help the people of Haiti.

If you’ve ever considered purchasing RxCalc now would be a great time to give it a try and in the process you’ll help people in need.

Also, while you’re here, take a look at all the great software being offered by Indie Relief, and pick something else up to help fight the good fight!

Thank You.

Evaluation of once-daily gentamicin dosing in children with febrile neutropenia

January 2nd, 2010

Jerry Fahrni

Once-Daily Gentamicin Dosing in Children with Febrile Neutropenia Resulting from Antineoplastic Therapy

Miriam Inparajah, B.Sc.Phm. | Cecile Wong, B.Sc.Phm. | Cathryn Sibbald, B.Sc.Phm. | Sabrina Boodhan, B.Sc.Phm. | Eshetu G. Atenafu, M.Sc. | Ahmed Naqvi, M.B.B.S., MCPS, MRCP | L. Lee Dupuis, M.Sc.Phm., FCSHP

Pharmacotherapy. 2010 Jan;30(1):43-51

Abstract

Study Objectives. To evaluate an existing once-daily gentamicin dosing guideline in children with febrile neutropenia resulting from antineoplastic therapy and, if necessary, to develop a new simulated dosing guideline that would achieve pharmacokinetic targets more reliably after the first dose.

Design. Pharmacokinetic analysis of data froma retrospective medical record review.

Setting. Hematology-oncology unit of a university-affiliated pediatric hospital in Canada.

Patients. One hundred eleven patients aged 1–18 years who received once-daily gentamicin between April 2006 and January 2008 for the treatment of febrile neutropenia resulting from antineoplastic therapy, and who had plasma gentamicin concentrations determined after their first dose.

Measurements and Main Results. Demographic data, gentamicin dosing information, blood sampling times, and plasma gentamicin concentrations were noted. Plasma gentamicin concentrations were determined at approximately 3 and 6 hours after the start of the 30-minute infusion of the first dose. Pharmacokinetic parameters were calculated according to standard first-order, one-compartment equations. The proportion of children who achieved pharmacokinetic targets after the first gentamicin dose was used as a measure of dosing guideline performance; the guideline achieved maximum concentration (Cmax) values below the target range (20–25mg/L) in 51% of patients. Ideal dosing guidelines were then developed using the mean dose required to achieved a Cmax of 23 mg/L for each patient. Univariate analysis or the Student t test was used to determine the existence of significant relationships between pharmacokinetic parameters and patient age and sex. The recursive binary partitioningmethod was used to determine critical values of age for dosage guideline development; analysis of variance was then used to compare the different levels obtained after use of this technique. Simulated administration of once-daily gentamicin in the following doses achieved a Cmax within or above target in 73% of patients: 1 year to 6 years, 10.5mg/kg/dose; girls ≥ 6 years, 9.5mg/kg/dose; and boys ≥ 6 years, 7.5mg/kg/dose. Doses were based on actual body weight for children who weighed less than 125% of ideal body weight or based on effective body weight for children 125%ormore of ideal body weight.

Conclusion. The initial gentamicin dosing guidelines were not effective in achieving Cmax. The new proposed dosing guidelines are predicted to achieve a Cmax within or above the target range in almost three quarters of patients. Subsequent dosing should be tailored according to plasma gentamicin concentrations.

Got Pharmacokinetics?

December 31st, 2009

Rob Fahrni

RxCalc IconThe year is coming to an end, so why not celebrate by purchasing a copy of RxCalc for your iPhone? There’s still time to buy before the end of the year and at $0.99 it’s a real bargain! At least we think it is.

So, what do you get for less than a buck?

  • New Start – Vancomycin and Aminoglycoside.
  • Adjustment with Levels – Vancomycin and Aminoglycoside.
  • Ideal Body Weight
  • Creatinine Clearance (CG)

That’s just the 1.0 release. We have more features planned for the next release and we’d LOVE to hear from our users, just drop us an e-mail at support@applecorelabs.com, it’s that easy.

If you’d like more information on RxCalc, just visit the RxCalc product page. If you’d like to purchase RxCalc, visit the iPhone App Store.