Effect of 99Tc on the radiochemical purity of 99mTc radiopharmaceuticals

The longer the time between elutions of a technetium-99m (Tc) generator, the greater the Tc : Tc ratio in the eluate. Information is limited on how this affects the radiochemical purity (RCP) of Tc radiopharmaceuticals. The aim was to determine whether the RCPs of Tc radiopharmaceuticals are affected when prepared using Tc-pertechnetate from a generator that remained uneluted for 7 days.

Eight Tc radiopharmaceuticals were investigated: albumin nanocolloid, macrosalb, medronate, mertiatide, pentetate, sestamibi, succimer and tetrofosmin. Five samples of each were prepared with eluate from a generator that had been previously eluted within 24 h (control). These were compared with five samples adulterated with Tc to replicate the Tc : Tc ratio present in eluate from a generator that has remained uneluted for 7 days (test). The RCP of each sample was measured 1 h after preparation and at the product's expiry.

Significant differences (P<0.05) were found between the RCPs of control and test samples of albumin nanocolloid, mertiatide and sestamibi 1 h after preparation. In each, the test sample had lower RCP, but was satisfactory. Similar results were found for macrosalb with added Tc, but the RCPs of the test samples were unsatisfactory at 83.9±4.2%. The RCPs of all control and test samples were satisfactory at expiry.

Seven of the eight radiopharmaceuticals tested can safely be prepared using eluate from a generator that has remained uneluted for 7 days. Under these conditions, care must be taken when preparing Tc-macrosalb, as its RCP remains unsatisfactory up to 2 h after preparation.