The invention provides an injectable formulation that includes an active agent; a biocompatible solvent system, crosslinkable polymers such as polysaccharides; and crosslinking agents; wherein the formulation is substantially free of water. The invention also provides a drug delivery depot formed from the injectable formulation wherein the polymers crosslink in the presence of water in the body of a patient, or in the air, prior to implantation in the patient. Also provided are methods of treatment using such formulations and drug delivery systems.