Assessment of 99mTc-succimer residual activity using inert nonreactive syringes

Abstract

It has been widely reported that 99mTc-succimer adsorbs to plastic syringes significantly (up to 50%), often resulting in a lower administered dose than intended or inaccurate dosing. This adsorption rate is especially problematic in the pediatric population. To improve 99mTc-succimer dosing, we compared the adsorption of 99mTc-succimer with 2 types of syringes: silicone-coated syringes with nonlatex rubber on the plunger and inert nonreactive syringes with no silicone coating and no rubber on the plunger. Methods: 99mTc-succimer kits were compounded according to the manufacturer's instructions. 99mTc-succimer doses (37-185 MBq) were drawn into 3-mL (silicone-coated or inert nonreactive) syringes in a 1-mL volume. Thirty min, 1 h, 2 h, and 4 h later, the syringes were assayed in a dose calibrator and assayed again after being emptied and rinsed with saline. In addition, we examined the data collected from 129 99mTc-succimer doses administered in a pediatric department, in which 52 were dispensed in siliconecoated syringes and 77 were dispensed in inert nonreactive syringes. The doses were assayed immediately before and after injection. The syringes were flushed with normal saline. Results: The labeling efficiency of the 99mTc-succimer kits was more than 95%. Residual activity left in the inert nonreactive syringes was 0.73% (SD, ±0.18%), which was significantly lower than the activity left in the silicone-coated syringes, 20.9% (SD, ±5.6%; P, 0.0001). The extent of adsorption did not change significantly between 30 min and 4 h of incubation. The clinical data showed that the residual activity was 30.6% (SD, ±12.5%) from doses dispensed in silicone-coated syringes and 6.38% (SD, ±2.95%) from doses dispensed in inert nonreactive syringes (P, 0.001). Conclusion: The inert nonreactive syringes had significantly less residual of 99mTc-succimer than silicone-based syringes, making it possible to accurately administer calculated doses of 99mTc-succimer to pediatric patients.