Preparation and storage of single-dose portions of exametazime: Effects on radiochemical purity after labeling

The effect of exametazime concentration, storage time, and the volume of the radiolabeling compound on the radiochemical purity of labeled exametazime doses was studied. Exametazime cold unit doses (CUDs) of 0.50, 0.33, 0.25, 0.17, and 0.13 mg/mL were prepared by reconstituting ex0ametazime kits with 0.9% sodium chloride injection. After either one or two days of storage at -10 °C, four CUDs of each concentration were labeled with 0.2-0.3 mL of sodium pertechnetate Tc 99m (10-20 mCi). The radiochemical purity of CUDs was evaluated 15 minutes later by instant thin-layer chromatography. In a second experiment, exametazime CUDs of 0.5 mg/mL were prepared. After 0-19 days of storage at -10 °C, four CUDs were each labeled with 0.2 mL of sodium pertechnetate Tc 99m (10-20 mCi), and radiochemical purity was measured after 15 minutes. In a third experiment, exametazime CUDs of 0.5 mg/mL were labeled with 2.0 mL of sodium pertechnetate Tc 99m (10-20 mCi) after zero to five days of storage at -10 °C. The mean radiochemical purity was unacceptably low (<80%) for exametazime CUDs of 0.33, 0.25, 0.17, and 0.13 mg/mL; the 0.5-mg/mL CUDs were acceptably stable. Purity was <80% for CUDs stored for more than two days. The radiochemical purity of CUDs labeled with 2.0 mL of sodium pertechnetate Tc 99m was significantly greater than the purity of CUDs labeled with 0.2 mL for storage times exceeding two days. Exametazime 0.5-mg/ml, CUDs frozen for five days produced radiopharmaceuticals with acceptable radiochemical purity after being labeled with sodium pertechnetate Tc 99m 2.0 ml. (10-20 mCi).