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 theo phylline were incorporated into cast chitosan films as model acidic and bas ic 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 C-13 NMR spectro scopy demonstrated the drug-polymer interaction between salicylic acid and chitosan, resulting in salicylate formation, whereas no drug-polymer intera ction was observed in theophylline-loaded chitosan films. Most chitosan fil ms loaded with either salicylic acid or theophylline exhibited a fast relea se pattern, whereas the high viscosity chitosan, films incorporated with sa licylic acid showed sustained release patterns in distilled water. The sust ained release action of salicylic acid from the high viscosity chitosan fil ms was due to the drug-polymer interaction. The mechanism of release was Fi ckian diffusion control with subsequent zero order release. It was suggeste d that the swelling property, dissolution characteristics of the polymer fi lms, pK(a) of drugs and especially drug-polymer interaction were important factors governing drug release patterns from chitosan films. (C) 2001 Elsev ier Science B.V. All rights reserved.