Hello Bhargavi,
Your main concern with the Generic SimBiology PBPK model version 1.2.1.1 is about the difference between the units for drug undissolved (mg) and drug dissolved (mg/mL). I went through the paper referenced in the creation of this model and it does have the units of drug dissolved in amount(mg) and not concentration(mg/mL), hence validating your problem.
Based on the community discussion on the Generic SimBiology PBPK Model, it can be observed that the file exchange model will detect the dimensions of the reactions before simulation and the volume of the compartment will be multiplied accordingly with the formula to balance the consideration of concentration dimensions similar to your case. Please refer to the below link for the community discussion for more details as it might be suitable and valid for your problem as well:
Hope it helps!
