Vancomycin is a difficult drug to dose because of extreme inter-patient variability of pk parameters. No single model will fit all patient populations.

• Look at the divergent models from the literature

• The Normal or CL model calculates a clearance and was derived from the work of Winter.
• The Outlier or Kel model calculates an elimination rate constant (Kel), and was derived from the works of Matzke.

Patients who may be more appropriately dosed with the outlier model include:

• obese patients (BMI > 30)
• underweight and/or malnourished patients
• nonambulatory patients (likely to have low muscle mass)
• diabetics
• patients with acute or chronic renal failure

Please bear in mind that vancomycin is not a very predictable drug, and these models will not fit all patient populations. It is important to save your data, and to periodically re-analyze your population parameters vs outcome.

You may analyze a single trough, a single peak, or a random level drawn at any point within the dosing interval by selecting the single point Bayesian method. On the Hand-held versions of Antibiotic Kinetics©, this method is designated by the abbreviation "B".

The serum level time is relative to the preceeding dose. For example:

• Vancomycin Q 12 hours
• Infused over one hour
• Trough level drawn 30 minutes before the dose

One way to grasp this concept is to understand that the serum level is the result of a dose which has been given, not from a future dose.

The difference is most likely due to the weight that you are using in your hand calculation. Because creatinine is produced by muscle tissue, C&G recommend that you use lean body weight, except in morbidly obese patients. Because creatinine is produced by muscle tissue, not fat, additional weight in form of fat does not significantly alter the production of creatinine.

There is considerable difference of opinion among practitioners concerning the most appropriate creatinine clearance equation to use. Antibiotic Kinetics© includes multiple creatinine clearance methods from which to choose. Use the method which is most appropriate for your patient. Please refer to this page for more information on creatinine clearance calculations:

Dosing of renally excreted drugs

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 plus 15 minutes after the injection.

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.

Please refer to this consensus document which appeared in the June 1997 issue of the International J. of Clinical Pharmacology and Therapeutics:

• Read "Once daily dosing of aminoglycosides"
• The PK/PD principles underlying the Hartford and consensus nomograms are sound. However many consider the nomogram approach to be an oversimplification. Patients should be individually dosed in order to maximize therapeutic efficacy and minimize the risk of toxicity. The dose should be large enough dose to produce a peak that is 8 to 10 times greater than the MIC. The dosing interval should then be extended to produce a trough less than 0.5 mcg/ml in order to provide a washout of aminoglycoside in the renal tubule thereby reducing toxicity.

The initial pediatric calculations are weight based, as they are in every pediatric reference book you will find. Although you cannot target a specific peak and trough, the program will show estimated peak and trough levels from your selected dose.

The reason that initial doses are weight-based is because the creatinine clearance equations for peds are not accurate enough to be used for pk modeling.

Times are relative the beginning and the end of the infusion.

• For pre-dose times, this refers to the beginning of the infusion, hence the instruction "minutes BEFORE infusion".
• For post-dose times, this refers to the end of the infusion, hence the instruction "hours AFTER infusion".

Unfortunately, late doses can not be avoided, so how can you use these levels? There are at least two late dose scenarios, each would be handled differently, depending on the methodology you are using.

The first late dose scenario we'll describe occurs if the dose was late but the levels were correctly drawn relative to the actual hang time. For example, the nurse is supposed to be giving gent 80mg Q 8 hours, at 6-14-20, but the sample dose is given late, at 1600. The trough was drawn at 1530 and the peak at 1730. As you can see, the levels are correctly drawn relative to the late dose.

First, let's examine the Sawchuk and Zaske method. This method is the gold standard for evaluation of peak and trough levels in the one-compartment open model. Sawchuk and Zaske drew three levels: a trough before the dose, a peak after the dose, and another trough after the dose. However, many institutions take a shortcut and only draw two levels, a trough before the dose and a peak after. If the patient is at steady-state, then you can assume that the second trough after the dose will be the same as the trough before the dose. Under most circumstances, this is a valid assumption and will save laboratory expenses.

Next, look at Sawchuk and Zaske's equations for calculating pk parameters, you can find them in the program help file (Press the F1 key). Where is the dosing interval in these equations? ...... nowhere! The dosing interval is not used in any calculation.

If you are using the 3-point method, the interval is not used, and it doesn't matter if the dose was given late, as long as the levels are correctly drawn, relative to the time the dose was actually given.

If you are using the two point method, the dosing interval is only used to extrapolate the pre-dose trough to simulate the after-dose trough. Therefore, in the Antibiotic Kinetics program, instead of entering the "ordered" interval, you would enter the time between the last dose and the sample dose. Using our same example, if the nurse is supposed to be giving gent 80mg Q 8 hours, at 6-14-20, but the sample dose is given late, at 1600. In the Antibiotic Kinetics program you would enter an interval of 10 hours. Again, this is because the interval is only used to extrapolate the pre-dose trough.

The second late dose scenario occurs when the dose is give late and the levels are correctly drawn relative to the scheduled hang time, not the actual hang time. For example, if the nurse is supposed to be giving gent 80mg Q 8 hours, at 6-14-20, the sample dose is given late, at 1600, but the trough was drawn at 1330 and the peak at 1530. As you can see the levels are correctly drawn relative to the scheduled dose, not the actual hang time, the "peak" is not a peak at all, but a trough drawn before the dose was given.

This scenario is the result of a lack of communication between lab and nursing. In this case, throw out the peak and just use the trough. With Bayesian you only need a single trough level.

The Antibiotic Kinetics program is deceptively simple in this area. When you hit a snag like this, you have to stop and think, and that's the downside to having such a simple interface for entering levels. The other alternative, and the one taken by most other PK programs, is to have you enter each and every dose and the time each dose was administered. This approach punishes you each time you have to enter a simple set of levels. The Antibiotic Kinetics program only makes you work hard in a problem situation.

The model editor is accessed from the program menu:

• Android
  1. Tap the Android menu button on the main screen
  2. Tap Model editor
  3. Tap the (+) button to create a new blank model
• PalmOS
  1. Tap Go To on the upper right of the main screen
  2. Tap Models
  3. Tap the (+) button to create a new blank model
• Windows desktop
  1. Click File on the MenuBar
  2. Click Edit Drug Models
  3. Click the [+] button to create a new blank model
  4. Or click the [cc] button to copy from the current model
• Windows Mobile
  1. Tap Edit on the MenuBar
  2. Tap Models
  3. Tap the [+] button to create a new blank model
  4. Or tap the [cc] button to copy from the current model

Unfortunately, this information is not found in one single reference. Bennett's Drug Prescribing in Renal Failure and Chernow's Critical Care Pharmacotherapy have tables of pk data for common drugs. The FDA package insert of newer drugs usually has an excellent pharmacokinetics section.

For a detailed tutorial on creating one compartment models, please see this page:

• View one-compartment tutorial

The following page contains a table of pk parameters for common antibiotics:

• View antibiotic pk parameters

The program does not make any specific adjustments for amputees, so you'll need to do some calculations the old-fashioned way. Enter the patient's pre-amputation height. The program will calculate a baseline lean body weight.

Because creatinine is produced by lean tissue, to get a more accurate estimate of CrCl, you'll need to estimate post-amputation muscle mass. Start with the LBW calculated from the patient's pre-amputation height. Then deduct a percentage depending on the extent of the amputation:

• Hand - Decrease LBW by 0.7%
• Forearm and hand - Decrease LBW by 2.3%
• Total arm - Decrease LBW by 4.9%
• Foot - Decrease LBW by 1.5%
• Calf and foot - Decrease LBW by 5.8%
• Total leg - Decrease LBW by 16%

In this case, since your patient is a double amputee, you would decrease the LBW by 32%. Let's call this the Amputee-Adjusted LBW (AALBW).

If the patient's actual weight is less than the AALBW, then the patient is underweight and you should use the patient's current weight to calculate CrCl.

If the patient weighs more than the AALBW, then you should hand calculate the CrCl using the AALBW.

References

1. John Murphy's Clinical Pharmacokinetics, 2nd ed. 2001
2. Brunnstrom, S. Clinical kinesiology. 4th ed. 1983

Good question. A patient may also have scoliosis or severe contractions that prevent a true height measurement. There are (at least) three methods that may be used to estimate height when actual measurement is not possible: knee height, forearm length and demi-span.

Estimating height in bedridden patients

We do not currently offer a native Mac version of Antibiotic Kinetics, however, please try the Web version which runs in the Safari web browser, it works perfectly on the iMac:

• RxKinetics Web App

Yes, there are versions available for the iPhone, please see the following for options:

• RxKinetics solutions for iOS

The "Bayesian Results" dialog displays several parameters which are used to evaluate the accuracy, reliability, and expected performance of the Bayesian derived model.

Interpreting Bayesian results

Yes.

All versions of 64-bit Windows (XP, Vista, 7, 8, 10) are able to run 32-bit programs seamlessly through WOW64 which is provided with the operating system and does not have to be explicitly enabled. In other words, it's 100% automatic. (Ref: Microsoft)

According to Microsoft, 32-bit software running under WOW64 has a similar performance to execution under 32-bit Windows. (Ref: Microsoft)

Antibiotic Kinetics© may be interfaced with a PIS, using our open interface specification. Our published interface is one-way, AbPK cannot access your eMR. Please contact your PIS vendor to request implementation.

RxKinetics software interface specs

The Antibiotic Kinetics© help file is a Windows compiled help file. For security reasons Microsoft has disabled viewing of CHM files over networks.

Please be aware that Antibiotic Kinetics is not network enabled, you may run into issues if you have multiple users accessing the program.

New versions of AbPK copy the help file into your local user folder. So, the fix is to upgrade AbPK.

Otherwise, you may read the the help on this web site:

Windows Desktop help

Antibiotic Kinetics© has had a built-in update checker since version 2.3.1, it is accessed via the Help menu:

There are four steps to the web update process.

1. Click Check button to access the RxKinetics web site to check for available updates.

   

2. If an update is available, a confirmation dialog will appear. Click the "Yes" button.

   

3. Next, a change log dialog is displayed.

   

4. A running program cannot be replaced.
   Therefore, you must exit Antibiotic Kinetics before installing an update. Web update will not proceed with the install step until you close Antibiotic Kinetics.
   After you have closed the Antibiotic Kinetics program, click the "OK" button to begin the update process.

   

Antibiotic Kinetics© version history

Your serial number is calculated specifically for your PDA, based on the information you provide us.

• The serial number for the Palm version is tied to your device HotSync ID, which is displayed on the program registration screen as "User name".
• The serial number for the Windows Mobile version is tied to your device owner name, which is displayed on the program registration screen as "User name".
• The serial number for the Android version is tied to the "My phone number" setting on your device.

No serial number is necessary to download Antibiotic Kinetics.

Antibiotic Kinetics Download Links

Yes, the Palm version runs slow on older, inexpensive devices like the Visor Deluxe or the Palm M105. These cheaper Palm devices use a very slow processor (Motorola Dragonball), which works fine for keeping track of appointments, but is slow when performing complex math functions.

I have used a speed hack called "AfterBurner" with these slow old Palms (available from PalmGear). The speed difference is noticeable, but not dramatic. Otherwise, if you have the need for speed, buy a new Tungsten, they scream.

You may have inadvertently changed your device indentification. Your registration code is specifically tied to your Palm HotSync ID. Therefore, if you change the device ID, you will need to get a new registration code.

You may request a new code from RxKinetics by sending an email with your old user name and your new user name (include as much information as possible for fastest processing - please provide your original order number to speed up the process).

Another simple solution is to just reset your Palm HotSync ID back to its original value. The following procedure will allow you to change your HotSync ID without affecting anything you have installed on your Palm device:

1. Run the Palm Desktop application
2. Select USERS from the TOOLS menu
3. Click on your HotSyncID in the list to select it
4. Click the RENAME button.
5. Type in your new/correct HotSyncID now very carefully
6. Click OK to return to the USERS Dialog
7. Click OK to exit out of the USERS Dialog
8. Exit out of the Palm Desktop Application
9. Do a regular HotSync - this will copy your corrected name down to your Palm device.

You may request a new code from RxKinetics by sending an email with your old user name and your new user name (include as much information as possible for fastest processing - please provide your original order number to speed up the process).

However, my advice to users replacing their Palm is to keep the same HotSync ID. When you use the same ID, HotSync will automatically transfer all your data (calendar, contacts, etc) AND all your software to your new Palm.

The following procedure will allow you to change your HotSync ID:

1. Run the Palm Desktop application
2. Select USERS from the TOOLS menu
3. Click on your HotSyncID in the list to select it
4. Click the RENAME button.
5. Type in your new/correct HotSyncID now very carefully
6. Click OK to return to the USERS Dialog
7. Click OK to exit out of the USERS Dialog
8. Exit out of the Palm Desktop Application
9. Do a regular HotSync - this will copy your corrected name down to your Palm device.

If you have the new Windows Phone, the only current option is the web app here:

• RxKinetics Web App

You may have inadvertently changed your device indentification. Your registration code is specifically tied to your device owner name. Therefore, if you change the device ID, you will need to get a new registration code.

You may request a new code from RxKinetics by sending an email with your old user name and your new user name (include as much information as possible for fastest processing - please provide your original order number to speed up the process).

Another simple solution is to just reset your device owner name back to its original value. The following procedure will allow you to change your device owner name without affecting anything you have installed on your PDA:

1. Tap "Start" then tap "Today"
2. Tap the word "Owner" on your PDA
3. Correct the Name
4. Tap "OK"

One of the database files has become corrupted. To fix the error, exit AbPK and erase the data files, they will be re-created when you re-start AbPK.

1. Exit out of AbPK.
2. Tap "Start", then "Programs" then "File Explorer"
3. Navigate to \Program Files\Antibiotic Kinetics
4. Tap and hold on the file "abpk_patient" then Tap "Delete"
5. Tap and hold on the file "abpkmodels" then Tap "Delete"

This is a known issue with version 1.x of AbPK for Pocket PC running on Windows Mobile (5 and up).

We recommend that you upgrade to version 2.x of AbPK for Windows Mobile (5 and up).

Another workaround to this problem is to use a task switching program. Once activated, the task switcher icon on the task bar enables you to see what programs are currently running on your PDA and provides a way to switch between running programs (and to shut down applications).

Some PDA manufacturers, like Dell, provide their own task switching program. If your PDA did not come with a task switcher, HandySwitcher is a 3rd party tool which works in a similar manner.

To duplicate the Tab key function, hold the shift key down while pressing the space bar.

Please download version 2.x which was specifically designed for Windows Mobile.

To switch between tasks on Android, perform a long press on the Home button, the task switcher will appear:

Yes, all screens, except the graph, are currently fixed in portrait mode. The GUI portion of Android SDK is very complex, every widget has to be hand-coded. I haven't had the time yet to redraw every screen for a landscape rotation, that will come in future versions. Please use the app in portrait mode. To edit a field, tap it and the software keyboard will popup. It's not a bug, it's a feature!

This is called a "nag" screen, you do not see this in the paid version. The purpose of a "nag" screen is to irritate you, and motivate you to purchase the paid version. I've spent six months of my life, working 10 hours a day to get this application out there. I don't think anybody works for free, do you? If you are using the app, please support my programming efforts. Your conscience and I will thank you.

With the "Jellybean" version of Android, Google added a new font size setting called "Huge". This font size is not compatible with AbPK. To fix:

1. Tap "Settings"

2. Tap "Display"

3. Tap "Font size"

4. Select "Large" (or Normal)

Thanks to David Jones for finding this out.

Yes, all screens, except the graph, are currently fixed in portrait mode. The GUI portion of Android SDK is very complex, every widget has to be hand-coded. I haven't had the time yet to redraw every screen for a landscape rotation, that will come in future versions. Please use the app in portrait mode. To edit a field, tap it and the software keyboard will popup. It's not a bug, it's a feature!

This is a known and often complained about problem with some Samsung devices.

The Samsung numeric keyboard looks like a phone call pad with no decimal point:

The workaround is to download a new keyboard app and set it as the default instead of Samsung. The Google keyboard is free:

Download the standard Google keyboard from the Play store

Then, in the language and input settings, make the Google keyboard the default.

The Samsung Galaxy S5 still has a menu button, it's just hidden. You only have to know where to look for it. Press and hold the multitasking key until the menu pops up. That's literally all there is to it. No black magic, it's just hidden behind the very button that replaced it.

Here is a youtube video if you need visual help with finding it:

• Samsung Galaxy S5: How to use the Menu button