Oral modified-release formulations in motion: The relationship between gastrointestinal transit and drug absorption

Oral modified-release dosage forms can be designed with the aim of achieving specific pharmacokinetic profiles, delivering to specific gut localities or reducing the number of drug administrations. Multiple-unit systems, such as pellets, beads or granules, often claim superiority to single-unit modified-release formulations in terms of predictability and reproducibility of behaviour in the gastrointestinal tract. This is an oversimplification and in this review we discuss the effect of the highly variable gastrointestinal transit on the bioperformance of multiple-unit dosage forms, relative to their single-unit counterparts. We examine the sometimes contradictory literature in this area and highlight specific case studies which demonstrate the effect of intestinal transit on dosage form performance and drug absorption.