Dextromethorphan resinates were prepared by a batch process and using 2 polysulfonate resins, namely Amberlite((R))IRP69 and Dowex((R))50W. The equilibrium time of drug loading depended on the degree of cross-linking and the particle size of the resins and was between 1-3 h. Amberlite((R))IRP69 produced dextromethorphan resinates with a broader size distribution when compared to those prepared from Dowe((R))50W. The release profiles of the resinates in simulated intestinal fluid, gastric juice and simulated gastric fluid showed sustained release characteristics. The major factors affecting drug release were the properties of the resin, such as particle size and degree of cross-linking. The release kinetics of the resinates could be analyzed using particle diffusion-controlled and film diffusion-controlled models. Moreover, this study also suggested that matrix diffusion-controlled model could be used as a new approach for evaluating the release rate of drug from the resinates. (c) 2005 Elsevier B.V All rights reserved.