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The following message was posted to: PharmPK
Hi,
I trying to run one compartment zero order absorption - (fixing Ka to Zero)
I could not calculate the "D" for this - is there an example for this?
Thanks in advance
Regards
Mouli
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Hi Mouli,
I am not sure what program you use and what D means. In principal, a zero-order absorption does not mean that the rate of absorption is equal to 0. What it means is that the amount of the drug absorbed is constant over time and independent of the drug concentrations or amounts in the lumen. You can think of the 0-order absorption as a constant infusion: the drug is infused (absorbed) with a certain rate for a period of time. The fact that you have a ka in your model's equations implies that you probably making a mistake.
Most modeling programs will require you to specify an amount(the dose) and a duration for the absorption time. You can estimate the duration as a model parameter.
Toufigh Gordi, PhD
Clinical Pharmacology, PK/PD analysis consultant
www.tgordi.com
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The following message was posted to: PharmPK
Dear Mouli,
As Dr Gordi has already indicated; you can solve this modelling problem by estimating the duration as a model parameter.
If you are using Phoenix WinNonlin 6.x then I can send you some example code for this as we actually perform an example of tweaking a library model to produce the user written model in our Introduction to Phoenix courses. I believe the equivalent WinNonlin 'classic' that is versions 5.x and earlier is available in Gabrielsson and Weiner's book, if you can't find it there I may be able to dig out a copy of that too.
I would also draw all Pharsight/WinNonlin users to www.pharsight.com/extranet where you can get tips and exchange model code with other users and may be a useful supplement to the PharmPK list.
Best regards,
Simon.
--
Simon.Davis.aaa.certara.com
Senior Scientific Consultant
Pharsight- A Certara(tm) Company
[Duration can also be modeled using boomer: http:www.boomer.org/
I've seen mention of problems with discontinuities when modeling this type of parameter but I have used boomer successfully in the past to model parameters like this, e.g. lag times - db]
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