A study of the concept of non-radioactive unit-dosed reagent kits [cold unit doses (CUDs)] as an efficient and cost-saving method for 99mTc radiopharmaceutical preparation

Traditionally, when preparing ^99mTc-labeled radiopharmaceuticals, [^99mTc]pertechnetate is added to the entire contents of a vial of reagent kit, and patient doses are subsequently withdrawn from the vial. This technique of compounding can be potentially wasteful for two reasons: (1) once reconstituted with ^99mTc, most reagent kits have a relatively short shelf-life, and thus the entire contents may not be used before expiration and (2) due to a need to conserve radioactivity in many hospitals, enough [^99mTc]pertechnetate is added to the reagent kit in order to retrieve only 1–2 patient doses, even though adequate chemicals (ligand, reducing agent, etc.) are present in the reagent kit to supply as many as 5–10 doses. Hence, a method for optimizing the efficient use of reagent kits would be desirable. The purpose of this study was to determine the feasibility of unit-dosing non-radioactive reagent kits and storing these cold unit doses (CUDs) for eventual labeling with ^99mTc. To evaluate this concept, unit doses were prepared from reagent kits of medronate (MDP) and pentetate (DTPA). The specific variables studied in this research were the effects of storage time, storage temperature and reconstitution volume (dilution) on the unit doses. These effects were monitored by measuring the radiochemical and biodistribution properties of the unit doses following their final reconstitution with [^99mTc]pertechnetate. The labeling efficiency was determined using instant thin layer chromatography (ITLC), and the biodistribution patterns of these radiolabeled CUDs were studied in mice. The results showed that MDP- and DTPA-CUDs stored at −18 °C retained the properties which resulted in acceptable radiochemical purity and biodistribution in mice for as long as 30 days. On the other hand, the radiochemical purity of MDP and DTPA unit doses stored at 25 °C deteriorated rapidly. Mean radiochemical purities as low as 0.58–19.4% were observed on day 30. Altered biodistributions were observed in a manner consistent with the decreased labeling efficiencies. The CUDs of lower dilution (3 mL) appeared to be more stable than the CUDs of higher dilution (10 mL). However, the effect of reconstitution volume was much less significant than the temperature effect on the CUDs. In conclusion, the concept of unit-dosing non-radioactive reagent kits appears to provide an efficient and cost-saving method for preparing infrequent and emergency radiopharmaceutical doses. The study also showed that the storage temperature of these unit doses is critical to the success of the procedure. The volume of reconstitution has a minimal impact on the stability of CUDs if stored at the appropriate temperature.