A cationic polymethacrylate coated multiparticulate diltiazem formulation exhibited sigmoidal drug release. Lag time prior to drug release was influenced by dissolution media, coat thickness, and by the nature of additives included in the formulation. Incorporation of up to 5% w/w sodium lauryl sulfate (SLS) in the coating membrane resulted in substantial increases in lag times in acidic and neutral media. The extent of drug release in acid was 100%, whereas in phosphate buffer, the extent of release was dependent on the level of SLS. Substituting SLS for various compounds was used to assess the functionality of the SLS molecule responsible for these behaviors. The ability to ion-pair with the polymer and the presence of a hydrophobic moiety were both important functionalities.