Takeichi Sakaguchi

The reaction of stannous ion with thiomalic acid in the preparation of 99mTc--thiomalate as a radiopharmaceutical.

The interaction of stannous ion with thiomalic acid has been investigated by potentiometric measurement. Evidence is presented for the formation of a complex having a 1 : 1 molar ratio of metal to ligand, as well as a monohydroxo complex. The stannous thiomalate complex reacts with 99mTcO4− to form reduced technetium species, which are then incorporated into thiomalic acid. When Tc-thiomalate is prepared by this method at pH > 5, 99mTc is excreted rapidly by the kidney. At pH = 2.5, however, 99mTc-thiomalate contains at least two different components, and one of the complexes is adsorbed on the gel as well as high affinity for the kidney while the other passed through the gel. The biological distribution using carrier 99Tc and 113sn indicates that there is little possibility of mixed metal complexes such as TcSn-thiomalate, and Tc-thiomalate is the most likely complex produced.