An improved ^99mTc-aprotinin kit formulation: Quality control analysis of radiotracer stability and cold kit shelf life

^99mTc-aprotinin scintigraphy has been demonstrated to be a useful noninvasive imaging technique for amyloid deposits located in extraabdominal regions of patients. The aim of this study was to develop an improved aprotinin cold kit formulation, to validate the kit for long-term stability, as well as to assess the radiotracer stability by novel quality control methods. The aprotinin cold kit formulation of Trasylol, pyrophosphate (PYP)-chelated stannous reductant and an alkaline buffer, was dispensed into nitrogen-filled vials and aliquots frozen at -20°C. After 0, 1, 2, 3 and 6 months of storage, three samples were reconstituted with 750-850 MBq of ^99mTc-pertechnetate, followed by quality control analyses by paper chromatography methods at 25, 85 and 265 min postreconstitution (pr). Cation-exchange cartridge quality control methods were also investigated. The cold kits proved to be stable to long-term storage for up to 6 months, and the radiotracer was stable for at least 4 h pr. ^99mTc-aprotinin was formed at greater than 95% efficiency at all time points tested with ^99mTcO₂ present as the major impurity (1-4%) and ^99mTc-pertechnetate and ^99mTc-PYP present in trace amounts. An alternative, rapid, safe and reliable method was found in Oasis MCX-BSA-treated cartridges using saline as the eluting solution to assay for ^99mTc-aprotinin.