Adsorption of radiopharmaceuticals to syringes leads to lower administeredactivity than intended

In this study we examined the delivered activity of radiopharmaceuticals in jected into patients and the various factors which lead to incomplete deliv ery. Four commonly used Tc-99(m) radiopharmaceuticals were included, namely pertechnetate, methylene diphosphonate (MDP), macro-aggregated albumin (MA A) and tetrofosmin. There was no appreciable residual activity after inject ion of pertechnetate and MDP other than that due to the dead space in syrin ges (0.06 ml, 4% of measured activity). However, there was considerable res idual activity following an MAA injection. This was particularly dependent on the radiopharmaceutical residence time in the syringe prior to injection . If MAA was pre-dispensed there was up to 80% of activity remaining in the syringe following injection. We have shown that this activity is not bound and can be decreased by agitating the syringe prior to the injection. For tetrofosmin, the activity remaining in the syringe was shown to be mostly d ue to adsorption of the tetrofosmin onto the plastic syringe (up to 30% of the activity); in particular, onto the rubber plunger. The amount of bindin g probably depends on the formulation of the rubber plunger and the plastic barrel, which varies between manufacturers. Of the three commonly used syr inge brands (Becton-Dickinson, Sherwood, and Braun syringes) the Braun syri nges were shown to have the least binding (6%) and would be most suitable f or tetrofosmin injection. We recommend the use of Braun syringes for tetrof osmin. We also recommend that pre-dispensed MAA injections should be gently agitated before injection into the patient. No special precautions are nec essary for pertechnetate or MDP injections. ((C) 2001 Lippincott Williams & Wilkins).