New bioerodible materials, which are noncrosslinked and water-soluble copolymers of quaternary amines, and alkyl (meth) acrylate were synthesized and then bound with anionic drugs (sodium sulfathiazole and diclofenac sodium) to form water-insoluble complexes. Sodium sulfathiazole was bound to the copolymers more strongly than diclofenac sodium. As the quaternary amine content of the copolymer was increased, the degree of binding of diclofenac sodium to the polymer increased (from 79.9 to 96.2%). Compressed tablets were prepared from the drug-polymer complexes, and their release profiles were well described by the dissociation/erosion mechanism. The release rate constant increased with increasing quaternary amine content of the polymer and decreased as longer alkyl methacrylates were used in the copolymer. The release kinetics were also dependent on the structures of the quaternary amines used (trimethylaminoethyl methacrylate chloride, trimethylaminoethyl acrylate chloride, and methacrylamidopropyltrimethylammonium chloride). Drug release from these systems were found to be independent of the ionic strength (0.05-0.2M NaCl) of the release medium.