In the present study, an attempt has been made to design controlled release colon-specific formulations of indomethacin by employing pH responsive polymers Eudragit (L100 or S100) in matrix bases comprised of xanthan gum. The prepared tablets were found to be of acceptable quality with low-weight variation and uniform drug content. In vitro release studies indicated rapid swelling and release of significant percentage of drug in the initial period from matrix tablets composed of xanthan gum alone. Addition of pH responsive polymers Eudragit (L100 or S100) to xanthan gum matrix resulted in negligible to very low drug release in the initial period in acidic to weakly acidic medium. Furthermore, with increase in pH of the dissolution medium due to dissolution of Eudragit L100/Eudragit S100 that resulted in the formation of a porous matrix, faster but controlled drug release pattern was observed. Thus, a sigmoidal release pattern was observed from the designed formulations suitable for colonic delivery. Drug release mechanism in all cases was found to be of super case II type, indicating erosion to be the primary cause of drug release. Since the drug release from almost all the matrix bases in the initial phase was negligibly low and followed with controlled release for about 14-16 h, it was concluded that a matrix design of this composition could have potential applications as a colon-specific drug delivery device with additional advantage of easy scale-up and avoidance of all-or-none phenomenon associated with coated colon-specific systems.

For the design and development of any novel formulation, assessment of compatibility of drug with excipients by different techniques such as thermal and isothermal stress testing are recommended. During pre-formulation studies common methods like UV-Spectrophotometric methods, FTIR are used for the study of compatibility. In the present investigation drug-excepient compatibility study of was conducted for metronidazole with ethyl cellulose to formulate microspheres by using different ratio of drug: polymer for colonic delivery. The drug and polymer mixtures were stored at 50 °C for 2 weeks. The samples were then characterized using UV Spectrophotometric method, FTIR. The results show that metronidazole was compatible with ethyl cellulose; hence ethyl cellulose can be used for formulation of metronidazole microspheres. Microspheres were prepared by modified Novel Quasiemulsification solvent-diffusion method to study the effect of ethyl cellulose on drug release with different proportions of metronidazole and ethyl cellulose. Prepared microspheres of ethyl cellulose were evaluated for size, morphology, sphericity study, percentage yield, loose surface crystal study, drug content and entrapment efficiency. In vitro drug release study was conducted by buffer change method to mimic Gastro Intestinal environment. The investigations revealed that microspheres prepared with metronidazole: ethyl cellulose ratio (1:2) show only 19.394 ±0.67% drug release in first 5 hours and 46.72 ±0.69% in 12 hours, which prove the potentiality of ethyl cellulose for colonic delivery of drugs.

Controlled release preparations have been reported to reduce the gastro irritant and ulcerogenic effects of non steroidal antiinflammatory drugs. In the present study, an attempt was made to develop matrix tablet-based controlled release formulations of ibuprofen, using ethyl cellulose as the rate-controlling polymer. In order to prevent initial release of the drug in the acidic environment of the stomach, cellulose acetate phthalate was incorporated in the matrix in varying amounts. It was found that with increasing the proportion of ethyl cellulose in the matrix, the drug release was extended for 14-16 h. Incorporation of cellulose acetate phthalate in ethyl cellulose matrix provided very low initial release of the drug in the first 2-3 h followed by enhanced release rate in alkaline medium owing to the high solubility of cellulose acetate phthalate at basic pH which led to creation of a porous matrix. It was concluded that combination of cellulose acetate phthalate with ethyl cellulose in the matrix base can be an effective means of developing a controlled release formulation of ibuprofen with very low initial release followed with controlled release up to 14-16 h.

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A pH- and time-controlled drug delivery system with sigmoidal release profile was developed using Eudragit (L100 or S100) in combination with hydroxy ethyl cellulose (HEC) or hydroxy propyl cellulose (HPC) for sigmoidal release of indomethacin in the potential treatment of colon cancer. The effect of varying proportions of polymer type on sigmoidal release was evaluated. The prepared tablets were also characterized for physical characteristics, in vitro drug release, release kinetics, and stability on storage. The gastrointestinal transit of formulations was also investigated in human subjects. Results from in vitro release studies indicated that due to the presence of pH-responsive polymers, a pH- and time-dependent release pattern was observed, which was characterized by negligible drug release in first 4-6 h followed by controlled release for 14-16 h in alkaline pH. In vivo studies indicated that HPC-based formulations had satisfactory matrix strength to withstand gastric and colonic transit, while HEC-based tablets disintegrated during transit through the small intestine. All the formulations were stable on storage. It was concluded that such a matrix design has good potential for drug delivery to colon with controlled release.