Antibiotic Kinetics© WebApp Help

What is a WebApp?

A web application (or WebApp) is a software application that is accessed over the Internet via web browser. WebApps provide cross-platform compatibility (i.e Mac, Unix, or Windows) because they operate within a web browser window. No additional software is "installed" on your computer, calculations are performed by a combination of client and server side scripts. Software updates are instantaneous as there are no files to distribute to individual computers.

The web pages on rxkinetics.net are formatted to fit the iPhone screen, but they will run under any W3 compliant browser (i.e Firefox, Internet Explorer, Safari). Unfortunately some mobile phone browsers may not be able to view the WebApp screens. Please visit the RxKinetics.com web site for PalmOS and Windows Mobile applications.

There are some subtle differences in WebApps versus traditional Windows applications. The most significant of these differences is the fact that field changes are not immediately recognized. Because there is no "OnChange" event, changes in an input field are not recognized until the data is submitted either by tabbing to new field or by clicking a button. The best example of this difference is the dose entry screen of Antibiotic Kinetics. If you change the recommended dose you must click the "Levels" button to recalculate the projected serum level estimates.

Your feedback is requested

Please, if you use these WebApps, I want to hear your feedback (positive or negative), and any suggestions you may have. Thank you, Rick.


Antibiotic Kinetics© Help Topics

Patient data

CrCl methods

View model

Serum level entry

Dose selection

Pharmacodynamic parameters

Serum level graph

Error messages

Frequently asked questions

Formulas and references


Patient data

Enter patient data by clicking on a field and then entering the data.

To choose an age unit, click the drop down selector to display and select the appropriate age unit for the patient: years, months, days.

Acceptable patient data
Parameter Acceptable range
Age 1 day to 110 years
Height 35 to 213 cm
Weight 2 to 251 kg
Serum creatinine 0.3 to 22 mg %

Creatinine clearance is calculated with the Swartz equation for peds. For adults, the Cockcroft & Gault equation using lean body weight is the default method.

To select a drug model, click the drop down selector to display and select from the available drug models.

Buttons

Click the CrCl button to select from other creatinine clearance methods.

Click the Calc button to calculate the creatinine clearance and to view Lean Body Weight (LBW) and Body Surface Area (BSA).

Click the Home button to return to the rxkinetics.net application selection menu.

Click the View model button to continue to the model entry screen. It is at this point that the program checks for acceptable and appropriate patient data. If the patient data is within the acceptable range, then the model screen is called.

Return to Help Topics


Other CrCl Methods

Click the drop down list to select a creatinine clearance method.

The following optional CrCl methods are for adults only. Please see the RxKinetics web site for a more in-depth discussion of CrCl methods.

Method Notes
C&G LBW Cockcroft and Gault method using lean body weight. This is the default method.
C&G ABW Cockcroft and Gault method using adjusted body weight.
 
A weight adjustment dropdown is displayed with this method. Select the percentage of excess weight that you wish to add to LBW.
C&G TBW Cockcroft and Gault using total body weight. Be aware that this method tends to over-estimate CrCl in larger patients. Therefore this method is not recommended.
C&G Normalized Removes weight from the C&G equation. Some find this variation useful in patients whose body size differs substantially from average.
Jellife 1973 Weight is not used in this equation either, therefore, some find this method useful in patients whose body size is substantially different from average.
MDRD (abbreviated) Derived from a large study of patients with a wide range of kidney function. It is important to note that MDRD calculates GFR which does not directly correlate to CrCl. Some feel this is a more accurate GFR method, however it may not be the best choice for pk models which are traditionally based on C&G.
Salazar and Corcoran Derived from a study of obese patients. Some recommend this method for obese patients instead of the standard equations.

Buttons

Click the Copy button to utilize the new CrCl value.

Click the Cancel button to return to the patient data window.

Equations utilized

Return to Help Topics


View model

This screen displays the population model and targets for your patient.

The parameters on this screen are:

Parameter Notes
Vd per kg Volume of distribution
in Liters per kg
Dosing wt Weight, in kg, used for the Vd equation:
Vd = DW x Vd per kg
Kel (or CL) Renal Renal portion of Kel or CL equation:
Kel (or CL) = Nonrenal + (CrCl x Renal)
Kel (or CL) Nonrenal Nonrenal portion of Kel or CL equation.
Target peak level mcg/ml
Peak time The time in minutes, after the infusion, at which you will be targeting your peak level.
Target trough level mcg/ml
Infusion time Length, in minutes, of the infusion.

Buttons

Click the Return button to return to the previous screen.

Click the Prospective button to calculate a dose using the population model parameters only, without serum level data.

Click the Retrospective button to enter and analyze serum level data for this model.

Return to Help Topics


Serum level data screen

This screen is displayed if you selected Retrospective on the view model screen.

Antibiotic Kinetics© supports multiple analysis methods. To select an analysis method, click the Select method drop down list:

Selection Details
Steady-state peak/trough Traditional steady-state trough before and peak after an infusion.
Non-steady-state 3-point Non-steady-state trough before the dose, and 2 levels after a dose.
First dose 2- or 3-point 2 or 3 levels drawn after the initial loading dose.
Steady-state 2- or 3-point 2 or 3 levels drawn after a steady-state dose.
Steady-state single point A single steady-state level drawn at any point after the infusion, Bayesian analysis only.
Extended interval A "random" level drawn 6 to 16 hours after a once-daily AG dose.

Please Note: all times are relative to the start or end of the sample infusion.

Please read the screen carefully when entering time data, some time entries are in minutes while others are in hours.

Buttons

Click the Return button to return to the previous screen.

Click the Clear all button to clear all data inputs.

Click the Calculate button to calculate individualized pk parameters based on your patient's serum level data. It is at this point that the program checks for gross errors in your data.


Serum level data analysis methods

Bayesian

Bayesian analysis is optional with the Trad and Post methods, and is always utilized with the B method. There are many precautions when using Bayesian, please read the RxKinetics pharmacokinetics tutorial.

Least Squares

If 3 post-dose levels are entered with the Post or 1st methods, then the data is fitted using least squares linear regression.

Extended Interval AG

Analysis of "once-daily" or "extended interval" aminoglycoside regimens is similar to that used by the "Hartford nomogram". If a 5mg/kg dose is analyzed, the "Consensus nomogram" is utilized. If the dose is 7mg/kg dose, the program will use the original "Hartford nomogram". Please visit the RxKinetics web site for further explanation.

Return to Help Topics


Dose selection screen

Prospective dosing
If dosing prospectively, using the population model, prior to obtaining serum level measurements, you may select a dosing method:

Option Description
Trad Traditional dosing
Adults: 1-cpt dosing based on your target peak and trough levels.
Peds: Ideal dose is weight-based.
EI Extended interval
Dose is wt based, interval is based on CrCl.
Note: EI dosing is only available in adults with a CrCl > 30 ml/min.

Retrospective dosing
EI or Trad option is disabled here because you chose the dosing method when you entered serum level data.

Dose entry
An "ideal" dose is displayed, you then enter a practical dose and interval.

Buttons

Click the Model button to view the patient-specific pk model parameters (Vd, Kel, etc.).

Click the Levels button to view the estimated serum levels from your selected dose.

Click the Return button to return to the previous screen.

Click the Graph button to view a plot of serum levels based on your chosen dose, and to e-mail a summary of your pk consult.

Click the PK/PD button to calculate pharmacodynamic parameters.

Return to Help Topics


Pharmacodynamic parameter screen

Enter the MIC then click the Calc PK/PD button to determine the following antibiotic PK/PD parameters:

Please visit the RxKinetics web site for further explanation of these PK/PD parameters.

Return to Help Topics


Serum level graph display

This screen displays a plot of the expected serum levels from your chosen dose.

The green line corresponds to the target peak, the red line corresponds to the target trough.

A summary of the model parameters and the patient data inputs are displayed below the graph.

Buttons

Click the Close button to return to the dose selection screen.

Click the Email button to e-mail a summary of the pk consult to your e-mail of record. Note: you must be logged in to a verified account to access this function.

Return to Help Topics


Frequently Asked Questions

1. What is the difference between the Vancomycin "normal" and "outlier" models?

Answer: Vancomycin is a difficult drug to dose because of extreme inter-patient variability of pk parameters. No single model will fit all patient populations. The two models roughly parallel two of the most popular one compartment models.

The outler model may be more appropriate for patients whose weight is significantly outside normal range.

Please refer to this page for more detailed information:
"PK Modeling of Vancomycin"

2. Why does the creatinine clearance from the Antibiotic Kinetics program differ from what I calculate by hand?

Answer: The difference is most likely due to the weight that you are using in your hand calculation. There is considerable difference of opinion among practitioners concerning the most appropriate weight and equation to use. Antibiotic Kinetics includes multiple CrCl equations, please use the method which is most appropriate for your patient population and your practice. Please refer to this page for more detailed information:
"Creatinine clearance and renal dosing"

3. Why is the default dose for once-a-day gentamicin 5mg/kg instead of Hartford's 7mg/kg?

Answer: Please refer to this consensus document which appeared in the June 1997 issue of the International J. of Clinical Pharmacology and Therapeutics:
"Once daily dosing of aminoglycosides"

4. How do I dose IM gentamicin?

Answer: Enter an infusion length of 90 minutes, which is the average time for IM absorption of aminoglycosides. Be sure to draw your peaks at least 90 + 15 minutes after the injection.

5. Must I always use steady-state analysis? For example, my patient received 2 doses of 1gm vanco q12hr, and for some reason the dose was decreased to 600mg around which levels were drawn.

Answer: You do not have to assume steady-state if you use the 3-point method. Draw a trough before the 600mg dose, a peak after, then a mid-point level after that. The program will use the pre-dose trough and the peak level to calculate the volume of distribution. The two post-dose levels are used to calculate the elimination rate.

6. What formulas are used in these calculations?

Answer: Please see the formulas page.


Donations welcome
 
If you find the RxKinetics WebApps to be useful in your practice, please donate to ensure their continued availability.

©Copyright 1984 - 2013, RxKinetics. All rights reserved