Injectable depot gel compositions and kits that provide an excipient formodulating a release rate and stabilizing beneficial agents are provided.Methods of administering and preparing such systems are also provided. The gelcompositions comprise biodegradable, bioerodible polymers and water-immisciblesolvents in amounts effective to plasticize the polymers and form gels withthe polymers. Suitable excipients include pH modifiers, reducing agents, andantioxidants.