Gastrointestinal contents in fasted state and post-lipid ingestion: in vivo measurements and in vitro models for studying oral drug delivery.

Lipids, either derived from food or used as drug delivery agents, can have a significant effect on orally delivered drug dissolution, absorption, and bioavailability. Despite numerous studies about fat-rich food/drug interactions, there is still an incomplete understanding of the influence of ingested lipids on oral bioavailability, and a lack of a general in vitro model that is able to predict a priori the in vivo performance of drug-lipid systems. In order to determine the impact of lipid and lipid digestion on drug dissolution and absorption, the choice of a bio-relevant in vitro model is the first and crucial point. A suitable in vitro model should include a medium that mimics as much as possible the gastrointestinal (GI) tract contents after food intake. The goal of this review is to provide an updated overview of (i) in vivo measurements examining stomach and intestine contents in fasted and fed states and (ii) the wide variety of bio-relevant media used in dissolution testing and in vitro lipid digestion studies. These approaches are compared and discussed in light of their capability to model physiological and physicochemical properties of GI tract contents in the fasted and fed states, and in particular when the lipid digestion process occurs.