Why we need proper PBPK models to examine intestine and liver oral drug absorption

Intestinal transporters and enzymes are factors that can influence the absorption of orally administrated drugs. Compartmental models are no longer adequate to describe the sequential handling of drugs and metabolites by the intestine and liver during oral drug absorption, especially when intestinal removal is substantial relative to the liver, and when induction/inhibition elicits different extents of change for identical intestinal and hepatic enzymes or transporters. In this review, we described PBPK models for the intestine (with differential flow patterns: traditional model, TM, and segregated flow model, SFM, and QGut model) as well as semi- or whole bodyphysiological- based pharmacokinetic (PBPK) models to describe the impact of the flow pattern, and the intestinal transporters and enzymes and their attendant heterogeneities on intestinal (FI or FG) and oral (Fsys) bioavailability. The modeling efforts have led to a refinement in providing mechanistic insight on the accurate prediction of drug and metabolite profiles for DDI, pharmacogenomics, age factors and disease conditions.