Preparation of 99mTc-ethylene dicysteine (99mTc-EC) by transchelation using 99mTc-glucoheptonate (99mTc-GHA) and its evaluation for renal function studies

The complexation of ethylene dicysteine (EC) with 99m Tc needs to be carried out at pH 12 to achieve a high radiochemical yield. However, the preparation of the kit at high pH poses difficulties and requires very stringent preparation conditions, as stannous tin, one of the main ingredients in the kit, is unstable at high pH. Hence, an alternative method, involving the transchelation preparation of 99m Tc-EC using 99m Tc-glucoheptonate ( 99m Tc-GHA) prepared at pH 6.5, was attempted, prompted by the reported success of the preparation of 99m Tc-sestamibi ( 99m Tc-MIBI) by this method. The preparation of 99m Tc-EC by this method first involved the formation of 99m Tc-GHA by the addition of sodium pertechnetate- 99m Tc to the Sn-GHA kit vial at pH 6.5. 99m Tc-EC was formed by the addition of reconstituted EC solution at pH ∼12 to the preformed 99m Tc-GHA. The reaction was allowed to proceed both at room temperature and on a boiling water bath. The pH of the final product was adjusted to pH ∼ 7 with 0.5 M phosphate buffer at pH 4-5, without affecting the quality of the product. The urinary excretion of 99m Tc-EC prepared by transchelation, tested in mice, was similar to that of directly prepared 99m Tc-EC, indicating that the final product prepared by the two methods was the same. The clinical evaluation of the product formulated by the new procedure showed satisfactory findings, comparable with the reports in the literature.