Multidose use of exametazine for leukocyte labelling: a new approach using tin enhancement

Reconstituted exametazime is inherently unstable due to the rapid oxidation of the small amount (7.6 micrograms) of stannous chloride present in the kit. A novel approach has been used to improve the shelf-life of reconstituted exametazime based on the premise that tin lost through oxidation should be replaced by further amounts of tin. Freshly prepared stannous solution, 0.1 ml (0.66 microgram Sn2+), was mixed with 0.3 ml (25 micrograms) exametazime solution followed by 400-500 MBq pertechnetate. Mixed leukocytes from 50 ml of patients' blood were labelled with 99Tcm-exametazime which had been prepared by the tin enhancement. One hundred and fourteen patients were investigated. The median labelling efficiency was 72%, range 30-96%. The exametazime had been reconstituted up to 5 months previously. Because of the small volumes of the exametazime solution used, up to 15 doses for leukocyte labelling could be prepared from one vial.