Dynamic Changes in Gastrointestinal Fluid Characteristics after Food Ingestion Are Important for Quantitatively Predicting the In Vivo Performance of Oral Solid Dosage Forms in Humans in the Fed State

How the Magenstrasse Is Formed After Meals: Protein Aggregation Hypothesis

Magenstrasse (stomach road) is reported to potentially influence the absorption of orally administered drugs by facilitating a gastric emptying of ingested water under postprandial condition. We hypothesized the Magenstrasse is a consequence of the formation of protein aggregates due to the decrease in gastric pH associated with stimulated gastric acid secretion. The formation mechanism of the Magenstrasse was examined in vitro using a gastric chamber system which reproduces postprandial conditions in the stomach. Oral liquid meals containing different amounts of proteins were mixed with simulated gastric fluid containing pepsin in the gastric chamber. When a high-protein liquid meal was used, infusion of gastric acid caused protein denaturation, generating semisolid aggregates. Then, to evaluate the impact of the aggregates, fluorescein isothiocyanate-dextran 4000 (FD-4) solution was added. The presence of protein aggregates facilitated the elution of FD-4 from the gastric chamber, indicating that the semisolid aggregates suppressed mixing of FD-4 solution with meals. In addition, formation of the same type of protein aggregates was observed in vivo in rat stomach after ingesting a high-protein liquid meal. These in vitro and in vivo results support the idea that protein aggregation of liquid meals in the stomach contributes the formation of the Magenstrasse.

Importance of Considering Fed-State Gastrointestinal Physiology in Predicting the Reabsorption of Enterohepatic Circulation of Drugs

PURPOSE

The purpose of this study was to develop a simulation model for the pharmacokinetics (PK) of drugs undergoing enterohepatic circulation (EHC) with consideration to the environment in the gastrointestinal tract in the fed state in humans. The investigation particularly focused on the necessity of compensating for the permeability rate constant in the reabsorption process in consideration of drug entrapment in bile micelles.

METHODS

Meloxicam and ezetimibe were used as model drugs. The extent of the entrapment of drugs inside bile micelles was evaluated using the solubility ratio of Fed State Simulated Intestinal Fluid version 2 (FeSSIF-V2) to Fasted State Simulated Intestinal Fluid version 2 (FaSSIF-V2). Prediction accuracy was evaluated using the Mean Absolute Percentage Error (MAPE) value, calculated from the observed and predicted oral PK profiles.

RESULTS

The solubilization of ezetimibe by bile micelles was clearly observed while that of meloxicam was not. Assuming that only drugs in the free fraction of micelles permeate through the intestinal membrane, PK simulation for ezetimibe was performed in both scenarios with and without compensation by the permeation rate constant. The MAPE value of Zetia® tablet, containing ezetimibe, was lower with compensation than without compensation. By contrast, Mobic® tablet, containing meloxicam, showed a relatively low MAPE value even without compensation.

CONCLUSION

For drugs which undergo EHC and can be solubilized by bile micelles, compensating for the permeation rate constant in the reabsorption process based on the free fraction ratio appears an important factor in increasing the accuracy of PK profile prediction.