How efficiently can Tilmanocept^® syringes be prepared?

Tilmanocept (Lymposeek^®) is used for isotopic identification of sentinel lymph nodes for patients surgically treated for malignancies. It is presented in a vial containing the kit for radiopharmaceutical preparation. The radiolabelling is carried out with 23.1MBq of ⁹⁹mTc in a volume of 0.625mL in order to minimize the injection volumes. The preparation of 18.5MBq in 4 syringes of 4.63MBq by the radiopharmacy is complicated by the small volumes and activities, the decrease in activity of ⁹⁹mTc, the adsorption of the product on the walls of the vial, and the necessity to get the required amount to perform quality control of the preparation. This work aims to describe an efficient and practical syringe preparation protocol to be implemented in our department.

Method
Preliminary tests were conducted without product to explore the various sampling techniques in accordance with Good Manufacturing Practice (GMP). Syringe volumes and activities, ease and safe handling were compared to define the best sampling technique.
When chosen, four radiopharmacy technicians each prepared three sets of Tilmanocept syringes and the difference to the target value of 18.5MBq was calculated and express in mean±sd%. A dispensation was considered compliant if this difference was lower than a 10% variation. In addition, the time in minutes was counted as from the start of the syringes preparation.

Results
The best sampling technique selected was the use of a 21G 2’’0.8 * 50mm needle (BD Microlance^®) inserted in the septum, reaching the bottom of the vial, so that the sampling could be performed using syringes (BD Plastipak^® 1mL) without ever having to flip the vial. The needle was never removed and some air was flared each time to safely disconnect the syringe. The syringes were equipped with 30G injection needles (BD Microlance^®) for assay and dispensation.
With this method, all the preparations were compliant with the target value and the mean variation value of -1.30±3.77%. Technician 1 had a mean variation value of -1.78%, technician 2 of +3.78% and technician 3 of +4.92%, technician 4 of -3.08%. The global mean time of preparation was 10±1 minutes. No kit was wasted. Every quality control was performed.

Conclusion
This repeatable sampling technique hereby described has enabled the radiopharmacy to dispense syringes that are compliant and contain the correct activity to perform quality scintigraphies. The only difficulty faced was to obtain the correct value of 23.1MBq in the vial for the radiolabelling. This study showed the importance of adapting radiopharmaceutical practices to new situations to comply with Summary of Product Characteristics and GMP.

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