Coating polymers for colon specific drug delivery: a comparative in vitro evaluation.

Colon is being extensively investigated as a drug delivery site. This study presents a comparison of the usual enteric coating polymers viz. Eudragit, cellulose acetate phathalate with shellac and ethyl cellulose, as carriers for colon specific drug delivery. Lactose based indomethacin tablets were prepared. These were coated with one of the coating polymers to a varying coat thickness. The coated formulations were evaluated for dissolution rates under simulated stomach and small intestine conditions. From the dissolution data obtained, it was found that the dissolution rate varied with the type and concentration of the polymer applied. Comparative dissolution data revealed that, of all the polymers and coat thicknesses used, a 3% (m/m) coat of shellac was most suitable for colonic drug delivery. It retarded drug release by 3-4 h (the usual small intestinal transit time) in simulated small intestinal fluid, whereafter a rapid drug release was observed.