The invention provides a carrier-linked prodrugs, wherein the biologically active moieties comprise at least one carboxylic acid and wherein the linkage between the drug moiety and linker is in the form of an ester wherein the hydroxyl group required for ester formation is provided by the linker moiety and the carboxyl group required for ester formation is provided by the drug moiety. The hydroxyl group of the linker is sterically hindered by the presence of an alkyl or aryl group on the carbon directly bound to or adjacent to the carbon carrying the hydroxyl group (a-carbon). The steric effect of the alkyl or aryl group enables greater control of the rate of hydrolytic degradation of such carrier-linked prodrugs.
