RE: Antwort: Re: change from mass to molar units

-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Thursday, March 08, 2007 9:32 AM To: Nick Holford Cc: [email protected] Subject: Antwort: Re: [NMusers] change from mass to molar units Nick, oh, sorry about that, that was a typo. I have mg and µg/L and µmol and nmol/L, so I'm afraid that's not the reason. I have a combined error model. However, although I needed the additive error to get the model to run, I fixed it to a very small value (0.0001). But to make sure I just adjusted this value too, with the same result. Just to get this clear for me...in theory the parameters should be the same, shouldn't they? So if this keeps on happening, what else can I do? I was thinking about recalculating the metabolite concentrations by dividing them with their molar mass and then multiplying with the molar mass of the parent. Would this be a reasonable approach, just to pretend that the metabolite is parent by using this calculation? Would the metabolite parameters still be correct then? Thanks for your help. Nele _________________________ Nele Plock Bayer Schering Pharma AG GPD/Pharmacokinetics Metabolism & Bioanalysis D- 13342 Berlin Phone : +49-30-468 15146 Fax: +49-30-468 95146 [EMAIL PROTECTED] Nick Holford <[EMAIL PROTECTED]> 08.03.2007 15:10 An [EMAIL PROTECTED] Kopie [email protected] Thema Re: [NMusers] change from mass to molar units Nele, Two suggestions: 1. You have mass units of mg and mg/L but molar units of nmol/1000 and nmol/L. So the ratio of AMT to DV is different by a factor of 1000 2. If you have an additive error model then the scale of the residual error model parameter will need to change. Best wishes, Nick [EMAIL PROTECTED] wrote: > > Dear all, > > I have fitted a simple two-compartment model with linear elimination to > some compound data (ADVAN4 TRANS4). Everything worked well. Because I want > to extend this model to account for metabolite data as well, I now wanted > to change all data to molar units, i.e. I changed the AMT and DV column in > the same way. To my understanding, if I change both these columns, the > obtained parameters should end up being the same. However, when I use mg > and µg/mL the model runs just fine, whereas when I use µmol and nmol/L the > parameter estimates change completely and always run into some boundary. > Can anyone shed some light on why this happens? Is there any way to get > around this? Could I keep the mass units and do some changes in the > control stream when incorporating the metabolite data? Any help would be > highly appreciated. > > Best regards > Nele > > _________________________ > Nele Plock > Bayer Schering Pharma AG > GPD/Pharmacokinetics > Metabolism & Bioanalysis > D- 13342 Berlin > > Phone : +49-30-468 15146 > Fax: +49-30-468 95146 > [EMAIL PROTECTED] -- Nick Holford, Dept Pharmacology & Clinical Pharmacology University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand email:[EMAIL PROTECTED] tel:+64(9)373-7599x86730 fax:373-7556 http://www.health.auckland.ac.nz/pharmacology/staff/nholford/ ************************************************************ The contents of this message are intended only for the use of the individual to which they are addressed and may contain confidential or privileged information. If you are not the intended recipient, you are hereby notified that any use, distribution, disclosure or copying of this message, any attachment or the information contained therein is strictly prohibited. If you have received this transmission in error, please notify the original sender immediately and delete all copies of this message, along with any attachments. Thank you. ************************************************************