PharmPK Discussion - One compartment zero order absorption

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• On 20 Aug 2010 at 12:46:25, Chandramouli Radhakrishnan (rcmoulirc.at.gmail.com) sent the message
`The following message was posted to: PharmPKHi,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 advanceRegardsMouli`
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• On 20 Aug 2010 at 11:31:07, Toufigh Gordi (tgordi.-at-.yahoo.com) sent the message
`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, PhDClinical Pharmacology, PK/PD analysis consultantwww.tgordi.com`
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• On 23 Aug 2010 at 04:23:39, Simon Davis (Simon.Davis.-at-.certara.com) sent the message
`The following message was posted to: PharmPKDear 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.comSenior Scientific ConsultantPharsight- 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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