The present invention relates in general to polymer-drug conjugates. In particular, the invention relates to polymer-drug conjugates wherein the conjugated drugs are selected from prostaglandins and substituted prostaglandins, to a method of delivering such prostaglandin drugs to a subject, to a sustained drug delivery system comprising the polymer-drug conjugates, to a method of preparing the polymer-drug conjugates, and to an implant comprising the polymer-drug conjugates. The polymer-drug conjugates may be useful for delivering prostaglandins and substituted prostaglandins for the treatment of glaucoma.