Film coatings for oral colon delivery.

Oral colon delivery is pursued through a number of formulation strategies with the aim of enabling effective and well-tolerated treatments for large bowel pathologies or enhancing the intestinal absorption of peptide and protein drugs. According to such strategies, coated dosage forms for colonic release may be provided with microbiota, pH, pressure or time-dependent polymeric films. Microbiota-activated coatings are mostly obtained from polysaccharides of natural origin mixed with insoluble structuring excipients. Alternatively, synthetic azo compounds have been employed, generally requiring organic solvents for use as spray-coating agents. On the other hand, pH-sensitive films show responsiveness to pH changes in the lower gut, such as the rise generally observed in the terminal ileum and distal colon or the slight acidification of caecal contents by bacterial fermentation products. Pressure-sensitive coatings are intended for rupturing because of the relatively elevated pressure that may affect solid dosage forms in the large bowel. Finally, time-dependent films are expected to undergo timed erosion, break-up or permeabilization processes irrespective of the aforementioned physiological variables. In this review, the differing films applied for colon delivery purposes are surveyed, and details on their composition, manufacturing and performance are reported.