Controlled drug release from implantable matrices based on hydrophobic polymers.

Reports on the controlled release of drugs, including macromolecular drugs, from silicone elastomers and ethylene-vinyl acetate copolymers, based on the formation of channels and cracks in the polymer, are reviewed. Aqueous interconnected pores are produced by osmotically active additives or by using loads of water-soluble drugs exceeding the percolation threshold. The release is generally proportional to the square root of time (t1/2). Nevertheless, pseudo-zero-order release kinetics can be obtained by adequately controlling the formulation variables. The factors controlling the release pattern and rate are discussed. In vivo applications of these types of systems are also considered.