Include different solubilities (fasting & fed) in a multiple-dose simulation

[miao-chan]

Hi everyone,

I am modeling a BCS class IIa compound that has different solubilities (FaSSIF & FeSSIF) under fasting and fed conditions. In PBS, the compound's ionization fraction at pH 4.5 is <10%, and in FeSSIF at pH 5, the ionization fraction is >90%.
As some clinical studies have mixed conditions (e.g., dosing following breakfasts/overnight fasting on PK day(s), and irrespective of food intake on the other days), I wonder whether there is a way to include different solubilities and assign them to different days in a multiple-dose simulation?
Currently, these trials are simulated with one of the solubilities according to the PK-day condition, assuming the other days have the same conditions.

Many thanks and kind regards,
Miao-Chan