# Simultaneous 3 compartment model plasma plus tissue **URL:** \ **Category:** Modelling and Simulation\ **Created:** [January 21, 2019, 1:47am UTC](https://forum.certara.com/t/simultaneous-3-compartment-model-plasma-plus-tissue/3381 "2019-01-21T01:47:50Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![vk\_pharmacy](https://avatars.discourse-cdn.com/v4/letter/v/f08c70/32.png) [@vk\_pharmacy](https://forum.certara.com/u/vk_pharmacy)\ **Post date:** [January 21, 2019, 1:47am UTC](https://forum.certara.com/t/simultaneous-3-compartment-model-plasma-plus-tissue/3381/1 "2019-01-21T01:47:50Z")
Hi, I have plasma as well as tissue concentration (Liver and brain) and I would like to develop 3 compartment model for the drug using all three concentration. Could anyone tell how to do in Phoenix NLME? How to prepare a data file and how to add 3 observation in the model? It would be great if someone shares the datafile preparation and show how to map in NLME. ---
**Author:** ![SimonDavis](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@SimonDavis](https://forum.certara.com/u/SimonDavis)\ **Post date:** [January 21, 2019, 6:49am UTC](https://forum.certara.com/t/simultaneous-3-compartment-model-plasma-plus-tissue/3381/2 "2019-01-21T06:49:37Z")
Morning, This should be fairly straightforward, at least in model definition. I think it would be easier to have the measurements for each compartment as their own column of data, e,g, c\_plasma, c\_brain, c\_liver. Choose a base model e.g. 2 compartments and then once you have chosen “edit graphical” you can right click in your model to add extra observations and compartments as required. I would look at the NLME examples guide, to become more familiar with the model building e.g. Graphically create a peripheral elimination model (page 177 in v8.1 documentation) and also look at some of the recorded PML school webinars e.g. [https://support.certara.com/forums/topic/1116-minimal-physiologically-based-pharmacokinetic-model-for-monoclonal-antibodies](https://support.certara.com/forums/topic/1116-minimal-physiologically-based-pharmacokinetic-model-for-monoclonal-antibodies). Try and that and if you get stuck post the project file back here and we can try to advise further. Simon. ---
**Author:** ![Samer\_Mouksassi](https://avatars.discourse-cdn.com/v4/letter/s/ce7236/32.png) [@Samer\_Mouksassi](https://forum.certara.com/u/Samer_Mouksassi)\ **Post date:** [January 21, 2019, 3:08pm UTC](https://forum.certara.com/t/simultaneous-3-compartment-model-plasma-plus-tissue/3381/3 "2019-01-21T15:08:30Z")
keep in mind that the compartmental models do not have physiological meaning except very few unique cases. If you are really looking for a model representing Brain and Heart you need to go into PBPK and PML can be coded that way you can make your PBPK a simplified one depending on your needs. As Simon mentioned you can have sperate columns or your can have one column with a differentiator between the observations at a given time point you might have one type of observation only and that is fine you can leave cells empty Phoenix understand empty cells. > [@vk\_pharmacy](#): > > Hi, > > I have plasma as well as tissue concentration (Liver and brain) and I would like to develop 3 compartment model for the drug using all three concentration. > > Could anyone tell how to do in Phoenix NLME? How to prepare a data file and how to add 3 observation in the model? It would be great if someone shares the datafile preparation and show how to map in NLME. ---
**Author:** ![vk\_pharmacy](https://avatars.discourse-cdn.com/v4/letter/v/f08c70/32.png) [@vk\_pharmacy](https://forum.certara.com/u/vk_pharmacy)\ **Post date:** [February 11, 2019, 7:51pm UTC](https://forum.certara.com/t/simultaneous-3-compartment-model-plasma-plus-tissue/3381/4 "2019-02-11T19:51:22Z")
Thanks for your reply. I was able to fit my model. ---
**Author:** ![sylim](https://avatars.discourse-cdn.com/v4/letter/s/ed655f/32.png) [@sylim](https://forum.certara.com/u/sylim)\ **Post date:** [January 24, 2021, 8:37pm UTC](https://forum.certara.com/t/simultaneous-3-compartment-model-plasma-plus-tissue/3381/5 "2021-01-24T20:37:43Z")
Hi, If we use a compartmental model to describe plasma (mg/mL) and tissue concentrations (mg/g), how do we estimate volume of distribution of the tissue compartments? We use k12_V1=k21_V2 to derive V2 in a typical two-compartment model. In this case, V1 is central Vd in mL and V2 is “tissue compartment volume” and in a different unit, g. Can we simply add V2 as a parameter to be estimated? That would seem to make the estimation of k12 and k21 more difficult. Thanks, any advice or help is appreciated. ---
**Author:** ![SimonDavis](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@SimonDavis](https://forum.certara.com/u/SimonDavis)\ **Post date:** [January 25, 2021, 11:42am UTC](https://forum.certara.com/t/simultaneous-3-compartment-model-plasma-plus-tissue/3381/6 "2021-01-25T11:42:24Z")
you may find parametising in clearance rather than micro constants gives more stable solutions.