Drug release from hydroxypropyl cellulose and polyethylene oxide capsules: In vitro and in vivo assessment

In this study, hard capsule shells produced using a heat-melting method, which involved heating polyethylene oxide (PEO, with a molecular weight (MW) of 200,000) or hydroxypropyl cellulose (HPC, with MWs of 80,000,100,000, and 370,000) powder in a mold, followed by inserting a suitably sized pestle in the mold in order to coat the melted shell materials (HPC or PEO) onto the pestle with a certain force. The water uptake and dissolution tests of these capsule shells were evaluated in acidic buffer, basic buffer, and water. Theophylline was selected as the model drug. The drug release rate decreased with increasing viscosity grades of HPC used as the shell material. In vivo studies were conducted in rabbits with the novel capsules, and comparisons were made with gelatin capsules. It was found that the pharmacokinetic parameters, including AUC_0-∞ and T_1/2, showed no significant differences among the various capsules. Correlations between the in vitro T_D50 values and several in vivo parameters were established.