In vitro characterization of coevaporates containing chitosan for colonic drug delivery

A relative simple drug delivery system in the form of coevaporates were prepared and analyzed. They were based on chitosan (CS), a polysaccharide that undergoes specific degradation by colonic enzymes. Enteric polymers, namely cellulose acetate phtalate (CAP) and hydroxypropylmethylcellulose phtalate (HPMCP), were incorporated, due to their insolubility in environments presenting low pH values. The systems were physically characterized, demonstrating that CS affects the swelling properties of the samples. The ability of these systems to reach the colonic region was assessed in vitro in simulated gastric, enteric and colonic fluids. Korsmeyer–Peppas and Weibull models were applied to analyze the drug release kinetics and the results suggested that the drug release from the coevaporates follows a complex release mechanism, in which several processes, including diffusion, swelling, and erosion, are involved and may occur simultaneously. The results demonstrated that it is possible to prepare relative simple drug carrier systems able to reach the colonic environment, since their swelling capacity can be controlled by varying the composition.