Protein-binding and urinary excretion of 99mTc(Sn)-MDP and 99mTc-MDP

In an incubation experiment the Human Serum Albumin (HSA) binding of 99mTc-MDP (electrolytically labeled) and 99mTc(Sn)-MDP is established. During the incubation some pertechnetate is formed and in the case of 99mTc(Sn)-MDP also some hydrolyzed 99mTc. The HSA binding of 99mTc-MDP is less than the HSA binding of 99mTc(Sn)-MDP as established with gel chromatography, TCA-precipitation, ammonium sulfate precipitation and ultrafiltration. TCA-precipitation seems to be an insufficient method for determining the protein binding of 99mTc(Sn)-MDP. The urinary excretion in rats shows only one 99mTc-compound in both cases. The bone seeking properties of the urine-excreted 99mTc-compound were confirmed in another rat.