Controlled delivery via hot-melt extrusion: A focus on non-biodegradable carriers for non-oral applications

Hot-melt extrusion (HME) has an esteemed place in the pharmaceutical industry with significant applications and advancements spreading over 30 years of development. Currently, the choice of matrix excipients is vast, expanding from all different kinds of synthetic polymers to natural carriers. Non-biodegradable polymers are among the most widely used excipients for long-acting controlled-release applications owing to their robustness, prolonged and predictable drug-release rates, which result in high patient compliance and successful treatment outcomes. This review article focuses on the latest updates regarding the two main non-biodegradable polymers applied in non-oral, controlled-release drug-delivery systems via HME: ethylene-vinyl acetate and thermoplastic polyurethanes and their applications in formulations such as films, implantable devices and intravaginal rings. The relations between polymer structure, physicochemical properties, polymer-drug interactions and, eventually, their effect on drug-release are discussed in detail. In addition, mathematical models characterizing the drug-release, various non-biodegradable polymers for HME-based formulations and current trends are described.