What in vitro tests can help predict in vivo intestinal absorption, and what is a common limitation of these tests?

• A. Caco-2 cell permeability assays; limitations include not capturing active transport differences in vivo and variability between laboratories
• B. UV spectrophotometry
• C. In vivo colon perfusion
• D. Membrane dialysis

Answer: (A)

In vitro permeability using intestinal cell models is used to forecast how well a drug will be absorbed in the gut. Caco-2 cell permeability assays are the most common example of this approach. They use a human intestinal–derived cell line that differentiates into enterocyte-like monolayers with tight junctions and relevant transporters, allowing measurement of apparent permeability as a proxy for absorption. This setup helps predict oral absorption and can be linked to the Biopharmaceutics Classification System.

A key limitation is that these models don’t replicate all aspects of the in vivo gut. Active transport and transporter–enzyme interactions can differ from the human intestine, so compounds that rely on specific uptake or efflux transporters may be misestimated. Additionally, there is notable variability between laboratories due to differences in cell source, culture conditions, passage number, and experimental setup, which can affect permeability readouts and their correlation to actual absorption.