Comparing the gastric emptying of 240 mL and 20 mL water by MRI and caffeine salivary tracer technique

Gastrointestinal fluid volumes are a crucial parameter for dissolution and absorption of orally taken medications. Most often 240 mL are used in clinical standard setups. Nonetheless, surveys in patient populations revealed dramatically lower volumes for intake of oral medications in real life and even in some clinical studies reduced fluid volumes are common. These reductions might have serious impact on pharmacokinetics. Thus, it was the aim of this study to compare the gastric emptying of 240 mL and 20 mL of water in 8 healthy volunteers. For investigation of gastric fluid volumes Magnetic Resonance Imaging with strongly T2 weighted sequences was used. Gastric emptying was additionally quantified via caffeine pharmacokinetics measured in saliva. The absolute gastric volumes after intake of 240 mL or 20 mL obviously differed by factor 10 but relative gastric emptying expressed as fraction per time was nearly comparable. Only slighter slower emptying after intake of 20 mL was observed. Salivary caffeine pharmacokinetics representing mass transfer from stomach to small intestine after intake of different volumes did not differ. The absorbed caffeine fraction and emptied gastric volume fraction correlated well after intake of 240 mL, but not after intake of 20 mL, indicating a higher influence of secretion on gastric volume measurements after intake of smaller volumes. Relative gastric emptying as measured with MRI and salivary caffeine method was only slightly delayed, thus transfer of orally administered drug fraction could be comparable even with lower fluid intake as can be seen by comparable caffeine pharmacokinetics. Nonetheless, the considerably reduced volumes might interfere with dissolution and absorption.