However, for solubility-limited drugs, human Fa may vary according to dosage , necessitating the investigation of the effect of the dosage. A mechanism-based Fa prediction method that converts drug solubility, diffusion, and membrane permeability into a mathematical model, known as the gastrointestinal unified theoretical framework (GUTFW) model, has been published . In this model, parameters such as solubility, diffusion, and membrane permeability were obtained experimentally, and Fa was calculated using these parameters considering the dose. Therefore, when these parameters are accurately expressed as experimental values, they are expected to exhibit good prediction accuracy for various compounds. However, if various parameters are predicted using only the compound structure, the calculated Fa could have an estimation error for the necessary predicted parameters, which inevitably reduces the prediction accuracy .