Eudragit E as coating material for the pH-controlled drug release in the topical treatment of inflammatory bowel...

During an attack of ulcerative colitis the colonic pH of normally 6.4-7.0 drops to values of 2.3-4.7. The objective of this study was to investigate an acid-soluble polymer (Eudragit E) as coating material for multiple units (mini tablets) with regard to its ability to allow drug release only under the acidic conditions of the inflamed colon. Mini tablets (diameter 3 mm) containing 20% (w/w) of the model drug dexamethasone with or without the mucoadhesive swelling agent carbomer 934 (neutralized) were coated in a small coating pan with different amounts of an organic solution of Eudragit E leading to coating thicknesses of 150-400 microm. Drug release from the Eudragit E-coated cores at pH 2.0-5.0 starts after 10-50 min due to the rapid dissolution of the Eudragit E film. At pH 6.8 lag times of drug release depend on the composition of the cores and the thickness of the coating film: In the case of the carbomer-containing cores drug release is induced by disruption of the coating film due to swelling of the cores and lag times (up to 20 h) increase overproportionately with increasing coating thickness. With no swelling agent in the cores drug release at pH 6.8 is delayed due to the low erosion/dissolution rate of Eudragit E. Lag times of drug release (up to 33 h) increase in a linear manner with increasing coating thickness. Thus, Eudragit E, protected against dissolution in the stomach by an enteric coating, is a suitable coating polymer for drug release in acidic regions such as the inflamed colon.