Drug physical state and drug-polymer interaction on drug release from chitosan matrix films.

Four different grades of chitosan varying in molecular weight and degree of deacetylation were used to prepare chitosan films. Salicylic acid and theophylline were incorporated into cast chitosan films as model acidic and basic drugs, respectively. Crystalline characteristics, thermal behavior, drug-polymer interaction and drug release behaviors of the films were studied. The results of Fourier transform infrared and solid-state 13C NMR spectroscopy demonstrated the drug-polymer interaction between salicylic acid and chitosan, resulting in salicylate formation, whereas no drug-polymer interaction was observed in theophylline-loaded chitosan films. Most chitosan films loaded with either salicylic acid or theophylline exhibited a fast release pattern, whereas the high viscosity chitosan films incorporated with salicylic acid showed sustained release patterns in distilled water. The sustained release action of salicylic acid from the high viscosity chitosan films was due to the drug-polymer interaction. The mechanism of release was Fickian diffusion control with subsequent zero order release. It was suggested that the swelling property, dissolution characteristics of the polymer films, pK(a) of drugs and especially drug-polymer interaction were important factors governing drug release patterns from chitosan films.