Characterization of the human upper gastrointestinal contents under conditions simulating bioavailability/bioequivalence studies

Purpose. This study was conducted to compare the luminal composition of the upper gastrointestinal tract in the fasted and fed states in humans, with a view toward designing in vitro studies to explain/ predict food effects on dosage form performance. Methods. Twenty healthy human subjects received 250 mL water or 500 mL Ensure plus(R) (a complete nutrient drink) through a nasogastric tube and samples were aspirated from the gastric antrum or duodenum for a period up to 3.5 h, depending on location/fluid combination. Samples were analyzed for polyethylene glycol, pH, buffer capacity, osmolality. surface tension, pepsin, total carbohydrates, total protein content, and bile salts. Results. Following Ensure plus(R) administration, gastric pH was elevated, buffer capacity ranged from 14 to 28 mmoL L-1 Delta pH(-1) (vs. 7-18 mmol L-1 Delta pH(-1)), contents were hyperosmolar, gastric pepsin levels doubled, and surface tension was 30% lower than after administration of water. Post- and preprandial duodenal pH values were initially similar, but slowly decreased to 5.2 postprandially, whereas buffer capacity increased from 5.6 mmol L-1 Delta pH(-1) (fasted) to 18-30 mmol L-1 Delta pH(-1) (p < 0.05). Postprandial surface tension in the duodenum decreased by >30%, bile salt levels were two to four times higher, luminal contents were hyperosmotic, and the presence of peptides and sugars was confirmed. Conclusions. This work shows that, in addition to already well characterized parameters (e.g., pH, and bile salt levels), significant differences in buffer capacity, surface tension, osmolality. and food components are observed pre-/postprandially. These differences should be reflected in test media to predict food effects on intralumenal performance of dosage forms.