Linus Großmann, Katharina Springub, Linda Krüger, Fabian Winter, Adrian Rump, Marie-Luise Kromrey, Robin Bülow, Norbert Hosten, Jennifer Dressman, Werner Weitschies, Michael Grimm

• Background The transit and distribution pattern of fluids in the small intestine is a key parameter for the dissolution and absorption of drugs. Although some information is known about the small intestinal water content after administration of fluid volumes and meals, the intestinal transit of orally ingested fluids and solutions has been barely investigated. The aim of this three-arm, cross-over, 9-subject human study was to investigate the transit of orally ingested water in the small intestine under fasting and postprandial conditions using MRI. To identify the ingested water, manganese gluconate, which can be identified with T1-weighted MRI sequences, was added as a marker. Using Horos (DICOM software), quantification of the distribution of Mn2+ ions in the gastrointestinal tract in fasted versus fed state (standard meal by FDA guidance and a light meal) was possible. The distribution and approximate wetted intestinal length was very similar in the fasting and postprandial states, suggesting rapid transport of water ingested after a meal through the chyme-filled small intestine in continuation of the “Magenstrasse” (stomach road). In some subjects, manganese gluconate reached deeper parts of the small intestine even more quickly in the postprandial state than in the fasting arm of the study. A deeper understanding of the behaviour of solutes in the gastrointestinal tract is fundamental to a mechanistic explanation for the kinetic interaction between food and drug intake (food effects).