A Novel Method to Radiolabel Gastric Retentive Formulations for Gamma Scintigraphy Assessment

Purpose. To develop a robust radiolabeling technique to enable evaluation of difficult to radiolabel gastric retentive formulations using gamma scintigraphy. The use of a successful radiolabel will allow accurate assessment of the gastric residence time of the formulations. Materials and Methods. The retention of two radionuclides, indium (¹¹¹In) and samarium (¹⁵³Sm), with and without further processing to improve radiolabel performance were evaluated in simulated gastric pH in vitro. The most successful formulation from the in vitro screening was further evaluated in preclinical and clinical studies. Results. In vitro evaluation revealed significant radionuclide leakage at pH 1.5 for most radiolabeling attempts. Radionuclide leakage at pH 4.5 was less pronounced. The most successful radiolabel was formulated by adsorbing indium chloride onto activated charcoal, followed by entrapment in a cellulose acetate polymer melt. This provided the best radiolabel retention under both pH conditions in vitro. The radiolabel also proved to be successful during preclinical and clinical evaluations, allowing evaluation of gastric retention performance as well as complete gastrointestinal transit. Conclusion. A simple, yet robust radiolabel was developed for gastric retentive formulations to be evaluated pre-clinically or in a clinical setting by entrapping the radionuclide in an insoluble polymer through a simple polymer melt process.