The effect of the molecular weight of ethyl cellulose on the drug release properties of mixed films of ethyl cellulose and hydroxypropylmethylcellulose

The effect of the molecular weight of ethyl cellulose on the drug release properties of mixed films of ethyl cellulose and hydroxypropyl methylcellulose has been studied by coating spherical granules with a film and measuring the release of a water-soluble model drug substance. Drug release was found to decrease with increasing molecular weight and on the addition of plasticizer. diethyl phthalate, to the films prepared from the low molecular weight grades. At molecular weights in excess of 35.000 (equivalent to a grade with a nominal viscosity of 20 mPas) the addition of a plasticizer had no effect on drug release. The results have been correlated with the mechanical properties of films prepared from the various molecular weight grades of ethyl cellulose, the rapid release with the low molecular weight grades being caused by the presence of cracks and flaws in the film.