Development of a novel drug release system, time-controlled explosion system (TES). I. Concept and design.

A novel controlled drug release system. Time-Controlled Explosion System (TES) has been developed. TES has a four-layered spherical structure, which consists of core, drug, swelling agent and water insoluble polymer membrane. TES is characterized by a rapid drug release with a precisely programmed lag time; i.e. expansion of the swelling agent by water penetrating through the outer membrane, destruction of the membrane by stress due to swelling force and subsequent rapid drug release. For establishing the concept and development strategy, TES was designed using metoprolol and polystyrene balls (size: 3.2 mm in diameter) as a model drug and core particles. Among the polymers screened, low-substituted hydroxypropylcellulose (L-HPC) and ethylcellulose (EC) were selected for a swelling agent and an outer water insoluble membrane, respectively. The release profiles of metoprolol from the system were not affected by the pH of the dissolution media. Lag time was controlled by the thickness of the outer EC membrane; thus, a combination of TES particles possessing different lag times could offer any desired release profile of the model compound, metoprolol.