Synthesis of 131I Iopamidol as a Tracer for Development of Iopamidol CT-Scan Contrast Agent

Abstract Computed Tomography (CT) Scan is a means of imaging/diagnostic method which is preferable in hospitals in terms of availability, efficiency and cost. Currently, CT contrast agent most widely used is the iodinated derivatives, due to its high X-ray absorption coefficient. Contrast agent is a medical preparation used in CT-scan modality which has capability of enhancing the performance of CT-scan to differentiate between target organs and surrounding tissues, and one of them is iopamidol. Development of iopamidol contrast agent requires several steps, i.e formulation, characterization, in-vitro and in-vivo tests prior to clinical study. To do in vivo study or biodistribution study in experimental animals, a radioactive iopamidol should be used to trace the compound throughout the body to predict its pharmacokinetics, and for that purpose a radioiodine (Iodium-131 or 131 I) labeled iopamidol will be used. Optimation in the synthesis of 131 I iopamidol was carried out by varying pH, temperature and reaction time to obtain 131 I iopamidol with high radiochemical purity of more than 90% as a requirement of radiopharmaceutical preparation. The radiolabeled product was characterized using HPLC and the labeling efficiency was measured by TLC. The optimum condition obtained was repeated 3 times and the product was tested for stability in room temperature. Characterization using HPLC showed that retention time (Rt) of radiolabeled iopamidol was close to that of native iopamidol at ∼ 6 min, indicating that 131 I iopamidol was already formed. Iodium-131 labeled iopamidol has been successfully synthesized with labeling efficiency or radiochemical purity of 96% ± 1%, and the optimum condition of 131 I iopamidol reaction was obtained at pH 9, temperature of 140°C in 5 minutes reaction time, and the product was stable in room temperature up to 7 days. It is concluded that radioiodinated iopamidol has been successfully synthesized and will be used in the formulation of iopamidol as a part of iopamidol contrast agent development for CT-Scan purpose.