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 exametazime kits with 0.9% sodium chloride injection. After either one or two days of storage at -10 degrees 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 degrees 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 degrees C. The mean radiochemical purity was unacceptably low (less than 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 less than 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.(ABSTRACT TRUNCATED AT 250 WORDS)