This collection of contributions from the European Network on Understanding Gastrointestinal Absorption-related Processes (UNGAP) community assembly aims to provide information on some of the current and newer methods employed to study the behaviour of medicines. It is the product of interactions in the immediate pre-Covid period when UNGAP members were able to meet and set up workshops and to discuss progress across the disciplines. UNGAP activities are divided into work packages that cover special treatment populations, absorption processes in different regions of the gut, the development of advanced formulations and the integration of food and pharmaceutical scientists in the food-drug interface. This involves both new and established technical approaches in which we have attempted to define best practice and highlight areas where further research is needed. Over the last months we have been able to reflect on some of the key innovative approaches which we were tasked with mapping, including theoretical, in silico, in vitro, in vivo and ex vivo, preclinical and clinical approaches. This is the product of some of us in a snapshot of where UNGAP has travelled and what aspects of innovative technologies are important. It is not a comprehensive review of all methods used in research to study drug dissolution and absorption, but provides an ample panorama of current and advanced methods generally and potentially useful in this area. This collection starts from a consideration of advances in a priori approaches: an understanding of the molecular properties of the compound to predict biological characteristics relevant to absorption. The next four sections discuss a major activity in the UNGAP initiative, the pursuit of more representative conditions to study lumenal dissolution of drug formulations developed independently by academic teams. They are important because they illustrate examples of in vitro simulation systems that have begun to provide a useful understanding of formulation behaviour in the upper GI tract for industry. The Leuven team highlights the importance of the physiology of the digestive tract, as they describe the relevance of gastric and intestinal fluids on the behaviour of drugs along the tract. This provides the introduction to microdosing as an early tool to study drug disposition. Microdosing in oncology is starting to use gamma-emitting tracers, which provides a link through SPECT to the next section on nuclear medicine. The last two papers link the modelling approaches used by the pharmaceutical industry, in silico to Pop-PK linking to Darwich and Aarons, who provide discussion on pharmacometric modelling, completing the loop of molecule to man.

Objectives: For the treatment of inflammatory bowel disease, the development of pH responsive modified release dosage forms is one of the most common approaches to achieve targeted drug delivery. In this study, the dissolution behaviour of eight different modified release (MR) products containing 800 mg mesalazine was investigated.Methods: The performance of the products was compared under simulated fasted state conditions using the paddle apparatus as well as the dissolution stress test device mimicking mechanical stress events of bio-relevant intensity.Key findings: The dissolution behaviour of the eight tested different pH-responsive MR tablets containing 800 mg mesalazine was dependent on the test conditions. Phases of mechanical stress with physiological intensity influenced the dissolution characteristics and caused in some cases accelerated drug release indicating possible dose dumping.Conclusion: The study demonstrates that besides the investigation of the pH dependency of drug release, the characterisation of the mechanical robustness of the dosage forms is an essential factor determining the dissolution characteristics of such pH-dependent targeted modified release tablets. The susceptibility of 800 mg mesalazine MR tablets towards mechanical stress may be one reason for undesired drug delivery in vivo.