How to build indirect response model?
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I want to bulid a population PK/PD model, in the PD part, I used the indirect response(IDR) model to illustrates my response data. The equation of the IDR model is below.
I have a question, each individual has their own baseling protein (Protein0), the protein is change from their baselline, how shoud I build the model and how to set protein0 ?
Protein = Kin - Kout*(1+Imax*Conc/(Conc+IC50))*Protein
Fulden Buyukozturk on 7 Oct 2022
If I understand your question correctly, your indirect response model is in derivative form as: dProtein/dt = kin - kout*(1+Imax*Conc/(Conc+IC50))*Protein, is that right? If not, can you elaborate on your question?
If so and if Protein is defined in units of mass, amount, or concentration, in other words if Protein can be described using a Species, you can use reactions to define input/production (kin) and loss (kout) processes. See the screenshot below.
If you'd like to define Protein as a measured dimensionless quantitiy or with units other than mass, amount, or concentration (that cannot be descibed by a Species) you can use a Rate Rule instead to define it as
Protein = kin - kout*(1+Imax*Conc/(Conc+IC50))*Protein
where Protein is a Parameter.
To address your question about different Protein baseline/initial values: I assume you're interested in applying different initial values to Protein for each individual during parameter estimation. Is that right? If that's the case, you can store these initial values in different Variants and apply these variants in a Fit Data program using Variants and Dose Setup table. Please see the screenshot below.
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