Mesalamine has been used for treatment of diseases like ulcerative colitis and chron's disease which affect the colonic lumen and require local drug action, rather than systemic effect.1 ; 2 Several research workers have worked on delayed release devices (with enteric coatings which can bypass the upper gastrointestinal tract) which can thereafter release the drug immediately or sustain drug release in the form of matrix tablets, capsules, pellets or multiparticulate systems.3; 4; 5 ; 6 They utilized pH dependent, time dependent approaches or polysachharide based systems or osmotic delivery systems.7; 8 ; 9
For colon targeted systems, two aspects have to be considered. First, the delivery device should be able to avoid drug release in the upper parts of gastrointestinal tract including the stomach and small intestine and secondly, the dosage form should be able to supply the drug in optimum therapeutic concentrations in the colonic lumen for intended duration of time. The retention time of dosage forms in the stomach usually averages to 2 h and in the small intestine from 3-4 h. Therefore, the lag time of drug release should be around 5–6 h.10 This can be done with enteric coating with suitable enteric polymers like Eudragit S100. However, Eudragit coated formulations may start releasing the drug in the small intestine, above pH 7.11 Therefore, the coating formulation should be optimized such that the effective drug release starts after 6 h of dissolution. After the enteric coat gives way to the core tablet and drug release starts, the drug release should be sustained in a manner that the drug is available at the site of action for required duration. In case of ulcerative colitis, the affected part may extend from small sections to the entire colon.12 Therefore the dosage form designed should be able to release drug at a sustained rate while travelling through the entire length of colon. The colonic residence time again varies from 6 to 48 h.13 Therefore, the dosage form intended to serve the entire colonic lumen should have a sustained release property to maintain the release throughout the day.