Alternatively, approaches relying on small intestinal transit time have been pursued, where formulations incorporating a predetermined lag phase in their release patterns are used. While this lag phase is programmed so as to cover the entire time span the dosage form takes to move from the duodenum down to the caecum, an outer enteric coating is required to circumvent its highly variable residence in the stomach. The delay phase starting on gastric emptying has been attained through functional polymer coatings or plugs that control the onset of release based on differing mechanisms, such as primarily water swelling, dissolution/erosion, rupture on expansion or increased permeability.

In this presentation, the rationale and main design strategies behind time-dependent approaches to oral colon delivery are reviewed and discussed.