Preparation and Biodistribution of ^99mTc-Pamidronate as Bone Imaging Agent

Labeling of Pamidronate (PAM) with ^99mTc was studied by a direct labeling method in the presence of SnCl₂•2H₂O as reducing agent. The influences of the concentration of SnCl₂•2H₂O, PAM concentration and pH value, reaction time on labeling yield were investigated. The optimum labeling was determined. The results showed that the radiochemistry purity of ^99mTc-PAM was more than 95%. Biodistribution studies in normal mice and rats showed very high uptake of ^99mTc-PAM and long retain in bone. ^99mTc-PAM was washed out from the blood very quickly. In addition, considerable uptake in the kidneys indicated this complex was excreted mainly by renal pathway. On the other hand, the radioactivity in liver, lung and heart was negligible. It could be known from SPECT images that ^99mTc-PAM would be an excellent bone-imaging agent. Bone uptake of ^99mTc-PAM was higher than that of ^99mTc-MDP in mice. This study suggested that ^99mTc-PAM was a promising bone imaging agent and further study was worthwhile.