Preparation and properties of 99Tcm-exametazime using stannous ion augmentation of fractionated cold kits

Fractionation of 99Tcm-exametazime enables several patients doses to be prepared from one vial. To overcome the disadvantages of storage at -70 degrees C, storage at higher temperatures was investigated with replacement of stannous ions before use. Kits were fractionated using a nitrogen-purged 0.9% w/v sodium chloride injection, sub-dispensed into five nitrogen-filled vials in an aseptic environment and stored at -20 degrees C. Under these conditions, exametazime vials failed quality control in approximately 1 week. However, the addition of stannous pyrophosphate solution (10 micrograms Sn(II) in 0.1 ml, prepared by aseptic dilution of a red blood cell labelling kit) immediately before 99Tcm-pertechnetate produced 90.1 +/- 1.6% (n = 8) lipophilic complex with a normal rate of decomposition. Biodistribution studies of this product in mice compared with the full kit showed identical brain and other organ uptakes. This product was used for cerebral imaging in patients with 90.5 +/- 3.3% lipophilic complex (n = 647) at approximately 3 min and produced excellent clinical results. It is concluded that stannous ion augmentation ('reboot') using approved Sn(II)-pyrophosphate kits is a viable option for institutions with facilities for aseptic preparation of fractionated exametazime kits, enabling substantial cost savings. Other advantages include removal of restrictions on generator eluate and 'rejuvenation' of expired kits.