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 131I) labeled iopamidol will be used. Optimation in the synthesis of 131I iopamidol was carried out by varying pH, temperature and reaction time to obtain 131I 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 131I 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 131I 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.