Adsorption of radiopharmaceuticals to syringes: setting up a reliable protocol for its assessment.

Background: It is well known that various drugs, including radiopharmaceuticals, may adsorb to plastic syringes to different extents. Some reports suggest that adsorption can reach levels of almost 50%. The consequence of adsorption of a radiopharmaceutical and subsequent inadequate dosing can include an inappropriate diagnostic response in patients, an increase in the duration of investigation or treatment, and an increase in cost.

Aim: To investigate the extent of adsorption of Tc-succimer to plastic syringes and to set up a reliable protocol for assessment of the extent of retention of drugs to single-use plastic syringes before a new syringe brand and/or radiopharmaceutical are introduced in a nuclear medicine department.

Methods: Radiopharmaceutical kits from two different manufacturers were compared for retention using syringes from three different producers. To assess the influence of dilution on retention, Tc-succimer preparations were further diluted with sodium chloride solution for injection. Syringes were filled to one-third of their capacity and incubated at room temperature before being emptied into vacuum vials. The radioactivity of the syringes was measured before and after emptying. The extent of retained radioactivity was calculated as a percentage of radioactivity in the syringe before emptying.

Results: Results show that adsorption of Tc-succimer considerably differs between syringe brands. The adsorption of undiluted Tc-succimer in 30 min may exceed 50%.

Conclusion: The findings show that measurement of retention in syringes and injection sets should be regarded as an essential aspect of quality assurance before radiopharmaceuticals, syringes and injection sets are used routinely.