The suitability evaluation of commonly used Tc-99m labeled radiopharmaceuticals stored in unit-dose syringes

Objectives The purpose of this study was to test radiochemical purity (RCP) and retained activity over time on commonly used Tc-99m labeled radiopharmaceuticals that have been stored in single-dose plastic syringes. At many institutions, unit doses of these radiopharmaceuticals are obtained from commercial nuclear pharmacies and they are usually stored in syringes for long periods of time before administration to patients. Typically the RCP and the residual activity left in the syringe are not measured before and after administration, respectively.

Methods Standard patient doses of MDP, sestamibi, sulfur colloid (SC), MAG3, filtered SC, and MAA labeled with Tc-99m were drawn up in plastic syringes. RCP tests were conducted at 0, 6, 12 and 18 hr after preparation. In addition, syringe residual activity post injection was assessed at 0 and 18 hr. A separate syringe of Tc-99m filtered SC was re-filtered at 18 hr and residual activity in the filter was assessed. Particle size of Tc-99m MAA was checked at 0, 6, 12, and 18 hr.

Results Each dose of the tested Tc-99m radiopharmaceutical passed the RCP tests with high percentages (92.6-99.9%). The table below shows the results of the retained activity for each patient dose (n=3). The retained activities of Tc-99m MDP and Tc-99m MAG3 were minimal (1.1-3.9%) and not included in the table. The residual activity of filtered Tc-99m SC left in the filter at 18 hr from three separate doses was 24.5%, 21.6%, and 23.7%. The particle size of Tc-99m MAA was within the acceptable range up to 18 hr.

Conclusions The RCP tests passed for each Tc-99m labeled radiopharmaceutical up to 18 hr stored in a plastic syringe. The residual activity left in the syringe was noticeably high for the following Tc-99m labeled agents: sestamibi, SC, MAA and especially filtered SC. The re-filtered data indicates that the particle size of filtered SC increased over time.