Hi, i'm looking for suggestions on how i can use the graphic model builder in Phoenix to build a PK/PD Emax model where both the drug and biomarker (Effect) are dosed together. Without going into too much detail, I am assessing drug activity in mice where animals receive a single oral dose of drug to block the target, and then one hour later the mice are challenged with a single oral dose of an endogenous biomarker. The inhibiting drug thus increases the exposure to the biomarker and decreases the formation of biomarker metabolites. So i'm looking for a way for the biomarker to have its own PK and simultaneously be the Effect, because the biomarker will have its own PK profile in the absence of drug.
The reason for this is because it allows me to test drug activity in wild-type animals which have very low concentrations of the biomarkers of interest. Much higher biomarker concentrations are expected in the disease state.