Development, current applications and future roles of biorelevant two‐stage in vitro testing in drug development

Objectives Various types of two stage in vitro testing have been used in a number of experimental settings. In addition to its application in quality control and for regulatory purposes, two‐stage in vitro testing has also been shown to be a valuable technique to evaluate the supersaturation and precipitation behavior of poorly soluble drugs during drug development. Key findings The so‐called ‘transfer model’, which is an example of two‐stage testing, has provided valuable information about the in vivo performance of poorly soluble, weakly basic drugs by simulating the gastrointestinal drug transit from the stomach into the small intestine with a peristaltic pump. The evolution of the transfer model has resulted in various modifications of the experimental model set‐up. Concomitantly, various research groups have developed simplified approaches to two‐stage testing to investigate the supersaturation and precipitation behavior of weakly basic drugs without the necessity of using a transfer pump. Summary Given the diversity among the various two‐stage test methods available today, a more harmonized approach needs to be taken to optimize the use of two stage testing at different stages of drug development.