# Assistance with 3 Compartment PK Model **URL:** \ **Category:** Modelling and Simulation\ **Created:** [December 9, 2016, 7:48pm UTC](https://forum.certara.com/t/assistance-with-3-compartment-pk-model/3086 "2016-12-09T19:48:56Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![csheme](https://avatars.discourse-cdn.com/v4/letter/c/7993a0/32.png) [@csheme](https://forum.certara.com/u/csheme)\ **Post date:** [December 9, 2016, 7:48pm UTC](https://forum.certara.com/t/assistance-with-3-compartment-pk-model/3086/1 "2016-12-09T19:48:56Z")
Hi all, I have setup a 2 compartment population PK (first order conditional estimation method)model for plasma concentration that seems to fit the data well by diagnostics. However, recently I did obtain some tissue (liver concentration) data that I would like to fit the tissue observations into the model. I imagine the new model to be a 3 compartment fit. central (plasma), secondary (liver), and peripheral, but have not been successful using the graphical interface to get any decent fit with tissue (liver observations) included. I know it is a first order absorption from SC injection site to plasma (central), first order distribution between central and peripheral (Q3) like the intercompartment clearance, michaelis-menten uptake to liver from plasma (Q4), first order elimination from plasma (CLp) and liver (Clliv), like the uptake rate from plasma to liver. Could you please assist with my model, I have the link below. [https://www.dropbox.com/s/qypn2cjukrqjukm/Project%20-CS.phxproj?dl=0](https://www.dropbox.com/s/qypn2cjukrqjukm/Project%20-CS.phxproj?dl=0) Thanks greatly, ---
**Author:** ![csheme](https://avatars.discourse-cdn.com/v4/letter/c/7993a0/32.png) [@csheme](https://forum.certara.com/u/csheme)\ **Post date:** [December 9, 2016, 11:26pm UTC](https://forum.certara.com/t/assistance-with-3-compartment-pk-model/3086/2 "2016-12-09T23:26:40Z")
Nevermind, this was solved, the model structure was off and poor initial estimates were used. ---
**Author:** ![minhaj](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@minhaj](https://forum.certara.com/u/minhaj)\ **Post date:** [December 10, 2016, 9:07am UTC](https://forum.certara.com/t/assistance-with-3-compartment-pk-model/3086/3 "2016-12-10T09:07:51Z")
Good to hear