Reformulation of a codeine phosphate liquid controlled-release product

Background: Ion-exchange resins have been successfully used to create drug formulations providing controlled drug release that are easy to swallow, are sufficiently stable, and have good taste-masking characteristics. The objective of the present study was to replace the ion-exchange resin in a proven delayed release codeine preparation with a new resin able to provide the beneficial properties of the original formulations without the need for Eudragit coating to comply with modern manufacturing regulations. Methods: Nine cationic exchangers with different particle meshes, form, and pore structures were optimally loaded with codeine and their respective in vitro codeine release profiles were compared using the USP XXIII paddle method. Results: The most favorable release profiles were obtained with Amberlite IR 69 F and with Dowex 50 × 8−100. The former was used to prepare the formulated drug-resin complexes as it was available in a pharmaceutically pure form. Both, the cough syrup and concentrate formulations exhibited drug release profiles equivalent to the nonformulated drug-resin complex. These profiles as well as initial free codeine levels, the purity, and the identity were moreover maintained for a storage period of at least 6 months. Conclusion: The in vitro dissolution profiles demonstrated that the use of ion exchanger is most suitable for the development of sustained release codeine formulations.