A polymer-drug conjugate includes a crosslinked polymer network comprising a biocompatible polymer and a multivalent covalent crosslinker, wherein the multivalent crosslinker comprises an active ingredient precursor covalently bonded through two or more bonds to the biocompatible polymer, and wherein the covalent bond is a hydrolysable bond. The drug can be for treatment of glaucoma and the free drug is biologically active and selected to lower eye pressure.
