Good Evening, I am interested in the work, I use PK-Sim Version 11.2, Let me know if you are interested.

Do you want to include in the model some interactions between the drugs. Are they impactinh each other's PK?

If not and you simply want to model the 3 drugs on its own it may be easier to model each seprately. You could also write a model with distinct parameters names for each drug, but this may become uneccesarily complictaed.