Coacervate microparticles useful for the sustained release administration of therapeutic agents

A composition comprising microparticles having a matrix structure, wherein the matrix structure comprises the reaction product of at least one cationic polymer, at least one anionic polymer, and a binding component, wherein the binding component is distributed throughout the matrix structure of the microparticle, wherein the binding component is one member of a specific binding pair comprising the binding component and a linking moiety, wherein the linking moiety is suitable for linkage with a variety of therapeutic agents;

• and wherein the composition further comprises a therapeutic agent, wherein the therapeutic agent is linked to the linking moiety, and the therapeutic agent is bound to the microparticles through the specific interaction of the linking moiety with the binding component.