Literature Review of Gastrointestinal Physiology in the Elderly, in Pediatric Patients, and in Patients with Gastrointestinal Diseases.

Oral bioavailability studies during the development of new medical entities or generic drugs are typically performed in healthy volunteers. Approved drug products are, however, used by patients with diverse disease backgrounds, and by pediatric and elderly patients. To provide the knowledge base for assessing the potential effects of age or co-morbidity on the in vivo performance of an orally absorbed, systemically active drug product, the literature regarding the gastrointestinal (GI) physiological characteristics (pH, permeability, and transit time) in children, in the elderly, and in patients with GI diseases (irritable bowel syndrome, ulcerative colitis, and Crohn's disease) is reviewed herein, with the knowledge gaps highlighted.