Solvent-exchange-based in situ forming implants: advances and challenges as long-lasting formulations

Introduction In situ forming implants (ISFIs) are long-acting drug delivery systems that solidify at the injection site, creating a depot for sustained drug release from days to months. Compared with preformed implants, ISFIs offer unique advantages, including easier and more convenient administration and simpler manufacturing. Among the different types, solvent-based ISFIs are the most extensively studied and developed formulations.