Preparation of Controlled-Release Particles Based on Spherical Porous Silica Used as the Drug Carrier by the Dry Coating Method.

A controlled-release formulation is a dosage form that could improve a patient's quality of life by reducing the frequency of administration, while ensuring the continued effect of the medicine and reducing the side effects. To prepare these controlled-release particles, a wet coating method in which a drug is coated with a controlled-release material using water or an organic solvent is used, but with this method, the coating process is very time-consuming and requires large amounts of energy for the drying phase. In addition, contact with water or an organic solvent may cause problems such as alteration of the drug. Therefore, the use of a dry coating method has attracted attention as a means of overcoming these issues. However, since the drug is fixed to the surface of a core particle, it is necessary to further coat it with a water-soluble material. We used spherical porous silica (SPS) particles, considering that the drug fixation via a water-soluble material would not be necessary if the drug were to be placed in the pores of these particles. We used SPS filled with theophylline (TP), a model drug, as the core particles. To prepare controlled-release particles (CRP), a controlled-release layer consisting of hydrogenated castor oil (HCO) was applied to the core particle surface by a dry coating method. The paddle method using 1% w/v polysorbate 80 solution as the test medium was employed to estimate the TP dissolution rate of the resulting CRPs. The 50% dissolution time of TP extended from 14 to 405 min with increasing the amount of the coated HCO. The Korsmeyer-Peppas model applied to the TP dissolution behavior yielded an n value of around 1. Moreover, the K value was comparable with the case in which a zero-order model was applied. It is thought that the dissolution of TP from CRPs will conform to the zero-order model.