The Advanced Compartmental Absorption and Transit Model

Modeling and simulation of oral drug absorption has been widely used in drug discovery, development, and regulatory submissions. Predictive absorption models are used to determine the rate and extent of oral drug absorption, facilitate lead drug candidate selection, establish a formulation development strategy, and support the development of regulatory policies. This section details the Advanced Compartmental Absorption and Transit (ACAT) model ¹  developed by Simulations Plus, which extends the capabilities of the pre-cursor Compartmental Absorption and Transit (CAT) model ²  to include in vivo drug behavior of first-pass metabolism and colonic absorption. After the detailed explanation of the ACAT model, the section then details the scientific principles behind the implementation of the ACAT model to simulate the effects of a variety of physicochemical, physiological, and formulation parameters on the absorption of drugs in the gastrointestinal (GI) tract.

The following topics will be covered:

• ACAT Model Schematic

• Dynamic Fluid Volume Model

• Fed State Physiologies

• Absorption Modeling of In Vivo Drug Behavior

• Drug Release Dosage Forms

• Solubility and Dissolution Models

• Precipitation Models

• Lumenal Degradation

• Absorption Models

• Saturable Metabolism in the GI Tract and Liver

• ACATPlus™

For details about the internal standards that were used to define the equations in this section, see Equation Standards.