ABSTRACT
This chapter discusses the anatomy and physiology of animal models that can accommodate human-scale dosage formulations and reviews published literature in which the same dosage formulations have been compared in humans and animals. It also discusses the role and limitations of animal models for the bioavailability and bioequivalence assessment of new human oral dosage formulations prior to their introduction into humans. Comparison of the stomachs of man, dog, pig, horse, rat, cow, and llama indicates that major differences exist in the structure and the function of the upper gastrointestinal tracts in these species. The presence of large valvelike circular folds and tiny fingerlike projections in the small intestine result in this region of the gastrointestinal tract having the largest absorptive surface area. The plexuses in the wall of the gastrointestinal tract function as a semiautonomous nervous system controlling motor and secretory activities.
