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 silicone-coated 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.
The adsorption or adhesion of radiopharmaceuticals to administration sets and syringes has been well documented (Table 1) (1–8). In a previous study, we found that 99mTc-succimer adsorbed to plastic syringes up to 82%, often resulting in a lower administered dose than intended or inaccurate dosing (9). This rate of adsorption is especially problematic with low doses used with the pediatric population, which led us to investigate syringes with clinically acceptable levels of adsorption.
Factors Affecting Adsorption
MATERIALS AND METHODS
99mTc-succimer kits were compounded according to the manufacturer’s instructions. 99mTc-succimer doses (37–185 MBq) were drawn into 3-mL type A, silicone-coated (BD 3 mL, 309572, B-D) and type B, inert nonreactive (Fig. 1) (HSW 3 mL, 4020-X00V0 2 mL [3 mL]) NORM-JECT (Henke Sass Wolf) syringes with a volume of 1 mL. Both syringe types are composed of a blend of laboratory-grade polyethylene and polypropylene in sterile individually wrapped packaging. 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 located in a tertiary care academic pediatric hospital licensed for 230 inpatient beds with approximately 7,000 admissions per year serving all pediatric subspecialties. A research protocol and application was submitted to the campus institutional review board and approved. The pediatric nuclear medicine department is staffed by 4 CNMTs who shared the responsibility of administering and recording the 99mTc-succimer doses. Doses were administered using a small-bore T-port extension set with 5 mL of normal saline divided over 2 rinses through the syringe and the administration set. The activity in the syringe was assayed immediately before and after injection, with decay correction figuring into the analysis.
Inert nonreactive syringe.
RESULTS
The labeling efficiency of the 99mTc-succimer kits was more than 95%. Residual activity left in the inert nonreactive syringes (Type B) was 0.73% (SD, ±0.18%), which was significantly lower than the activity left in the silicone-coated syringes (Type A), 20.9% (SD, ±5.6%; P < 0.0001) (Table 2). The extent of adsorption did not change significantly between 30 min and 4 h of incubation. One hundred thirty-four data points were collected, with 129 included in the analysis. Of these, 52 were dispensed in Type A syringes, and 77 were dispensed in Type B syringes. 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) (Table 2).
Results
DISCUSSION
This study demonstrated that syringe B had significantly less residual than syringe A. Previously with syringe A, the clinic was calculating the low pediatric doses and adding additional activity to compensate for variable adsorption loss, in which the correlation between assayed activity and administered dose was 0.94. This method of dose calculation confounded efforts to lower the recommended minimum dose and reduce the radiation burden to the patient. As a result of the study, the clinic changed the ordering procedure for the patient population, eliminating the arbitrary addition for residual loss. With syringe B, the correlation between assayed activity and administered dose was 0.99. The 5 injections not used in the analysis were from the same technologist who did not rinse the syringe during administration. Keskintepe et al. have shown that administration technique can greatly affect residual (10). In a controlled environment, the adhesion was less than 1% regardless of incubation time with the inert syringes (syringe B). In the clinic, syringe B still had a much wider range for adsorption, indicating variances with rinsing technique or difficult patient dynamics at times. The technologists did report that the new method called only for 2 rinses with normal saline versus previously using 4–5 rinses to reduce the 99mTc-succimer residual. One problem reported was from the staff pharmacists drawing the doses. There is a small learning curve to overcome the increased resistance in syringe B. In order to have a liquid-tight seal as the piston moves through the barrel, the barrel in syringe B flexes to accommodate the slightly larger diameter piston tip. Swanson et al. studied 6 syringe brands, 1 of which showed a significantly low adhesion of 5.2% ± 2.5% with 99mTc-sestamibi, and concluded that much of the adhesion appeared in the syringe barrel and the plunger, with minimal residual activity in the butterfly and tubing (1). Overall, the selection of a low-adhesion syringe gives more reproducible residual activities and reduces the dispensed activity used in clinical procedures. This type of inert nonreactive syringes with no silicone could be used for other radiopharmaceuticals with high syringe adsorption reports such as 99mTc-tetrofosmin (7) and 99mTc-sestamibi (1).
CONCLUSION
The inert nonreactive syringes had significantly less average residual than the commonly used silicone-coated syringes. This change made it possible to eliminate the arbitrary addition of activity to account for residual loss and more accurately administer desired doses in this pediatric population.
DISCLOSURE
No potential conflict of interest relevant to this article was reported.
Acknowledgments
We thank Ann Kirkpatrick and the staff of the University of Oklahoma Nuclear Pharmacy and the following faculty and staff of the OU Medical Center: Dr. Leann Smith, Kim Brush, and Jean Nelson.
Footnotes
Published online Dec. 23, 2014.
REFERENCES
- Received for publication August 29, 2014.
- Accepted for publication November 5, 2014.
