Study of biopolymers as carriers for controlled release

An attempt was made to compare swelling and release behavior of two polysaccharides, xanthan gum (XG) and hydroxypropylmethyl cellulose (HPMC), taking into consideration their dissolution characteristics. This study was expected to provide information about the capability of these polymers to satisfy specific requirements in the design of controlled release systems. Tablets were prepared from the pure polymers as well as by using mixtures of XG and HPMC containing 1, 2, and 5% salicylic acid (SA) as a model drug. Swelling and dissolution experiments were run and the release in distilled water was recorded as a function of time. The results showed that XG and HPMC are very interesting matrices for the preparation of controlled release systems. Complete administration of SA in concentrations from I to 5% takes place within about 10 hr for XG, whereas approximately 5 days are necessary for the same result in the case of HPMC tablets. For both systems, nonFickian behavior was recorded with the diffusion exponent ranging from 0.67 to 0.78. Upon fitting the release data to the Peppas and Sahlin heuristic model, it was clear that, in general, erosion was the predominant factor for SA release from XG tablets, whereas the acid delivery from HPMC mainly proceeds via Fickian diffusion. These results seemed to be dependent on the water solubility of the released substance.