How do I perform nonlinear regression with phoenix? I really can’t find anything! Thanks, Georgia
Dear Georgia I guess you mean using an equation for the response, response that is non linear with respect to the model parameters. Suppose you have the response given by E=exp(Emax)/(1+exp(Emax)) The easiest way to deal with this kind of model is to take the Emax model from built in and consider it as your template. You then copy that model to the workflow and shift to “edit as textual”. You highlight the whole text of this model, create a new model textual and paste the content of the previous model. You then edit that model. I attached a simple example that shows you the steps. Note that almost all models in Phoenix are non linear but most are handled through use of differential equations or with built in equations like the 1 compartment model but that handle automatically multiple dosing. If you have a model that applies only to single dose and not in the PK libraries, then it is not trivial to use it for multiple dosing unless you can define it through a set of differential equations. If you can tell me the equation you are thinking about, then I can help you more. Best Serge [file name=nonlinearregressionmodelequationexample.phxproj size=192644]Certara | Drug Development Solutions (188 KB)
Hi Serge, It is supposed to be a simple exercise-the students will be given a set of iv bolus data and then they have to perform two nonlinear regression analyses: one with the explicit equation for C vs t (F=Aexp(-at)+Bexp(-bt) and one with differential equations. Then, they have to assume a 2cpt model and perform a simulation to predict the concentrations of the 2nd cpt. So, I am trying to solve the first part and I can’t find how to do it in Phoenix. Thanks for your help, Georgia
Georgia, I think you are maybe making it too complex… The software is called xxx"NonLin" because a lot of these models are prebuilt, e.g. If you want you use the older WinNonlin model engine then simply insert a PK model into your workflow and you will see the equations are already there for the appropriate model e.g. two compartment IV bolus would look like this 
If you want to get your students into writing code then the newer Phoenix model will probably be easier since the code is always displayed in the tab model text and you can move from built-in to graphical editing to textual editing. If you’re confused still please just attach your data sheet as Excel or CSV and I will start a Phoenix project for you. Simon 
Thanks Serge! I think too much POPPK makes you forget the basics! That’s what happened to me! Thanks again for your response, Georgia