Ion Exchange Resins as Excipients for Drug Delivery: Issues for Reproducible Drug Loading

A method for repeatable loading of propranolol hydrochloride as a model drug onto the ion exchanger Amber- lite TM IRP69 was developed and different parameters for the loading process were evaluated due to their impact of the ex- tent of loading. It was found that the extent of loading in equilibrium is widely independent of the experimental method used. However, a magnetic stirrer comminutes the ion exchanger particles, which hampers repeatable loading processes. For kinetic studies, it was found that the pharmacopoeia dissolution tester gives best repeatable results compared to other stirring devices (magnetic stirrer or shaking bath). Furthermore, evaluation of the loading profiles revealed complex kinet- ics, which can be best described by (at least) two independent processes. In addition, with different ratios between ion ex- changer and propranolol, the degree of loading in the equilibrium follows an adsorption isotherm of the Langmuir type, and predicts loading capacity.