Insight in the role of resistant starch and Eudragit S 100 in a coating for controlled release in the colonic region

A dual trigger coating was designed by Ibekwe et al. to achieve site-specific delivery of therapeutics to the colon. It consists essentially of Eudragit® S 100 (EU S 100), a polymer that dissolves above pH 7, and resistant starch, which can only be degraded by enzymes produced by colonic bacteria. Both components should maintain the integrity of the coating until reaching the colonic region and ensure drug release when reaching it. The contribution of these components was investigated in the present study by permeability testing and enzymatic degradation testing of free polymer films produced using an in-house built spraying device.

Diffusion testing of EU S 100 films showed no impact of the pH (2, 4, 6) and plasticizer levels (25, 30, 35 % w/w triethyl citrate (TEC)) on the permeability of the films. The permeability of the resistant starch-Eudragit® S 100 (RS-EU S 100) films was also not affected by the pH, however, the permeability coefficient of films containing 35 % w/w TEC was significantly higher for all pH levels. Incubating the RS-EU S 100 films with enzyme resulted in a higher permeability for films with 25 % w/w TEC, yet the presence of enzyme had no effect on the permeability of 35 % w/w TEC films. For the 25 % w/w TEC films, even if EU S 100 does not dissolve (pH < 7), the resistant starch in the RS-EU S 100 film can be enzymatically degraded.

Using n-butanol in the preparation process of the RS-EU S 100 films resulted in a lower permeability coefficient compared to the RS-EU S 100 films without n-butanol for all pH and plasticizer levels. n-Butanol forms a V-type complex with amylose, which makes the films less susceptible to enzymatic degradation.

The permeability and susceptibility to enzymatic degradation of the RS-EU S 100 coating can be adapted by altering the amount of plasticizer and the use of n-butanol during the production process.