Evaluation of compatibility and stability of filtered 99mTc-sulfur colloid when combined with fluorescent indocyanine green dye

It is a common practice to administer dyes and radiopharmaceuticals separately for the localization of sentinel nodes in patients with biliary tract malignancies. The objective of this study was to evaluate the chemical properties and particle size of filtered (99m)Tc-sulfur colloid before and after it is combined with indocyanine green for injection. This study also evaluated the compatibility and stability of the two when combined, for the possibility of a single injection. (99m)Tc-sulfur colloid was prepared according to the package insert, and the final preparation was passed through a sterile 0.2-μm filter. Green dye was also prepared as per the package insert. In a sterile syringe, 0.25 mL of 14.8-MBq (400-μCi) filtered (99m)Tc-sulfur colloid was mixed with 0.25 mL of 1.25-mg green dye in a 1:1 proportion for a total volume of 0.50 mL. The radiochemical purity and pH of filtered (99m)Tc-sulfur colloid were obtained immediately and at 1 and 2 h after preparation. Particle size was analyzed using an electron microscope immediately and at 2 h. The average radiochemical purity was 97.6% ± 2.0% (n = 51). The average pH was 5.56 ± 0.26 (n = 51). Evaluation of the particle size of filtered (99m)Tc-sulfur colloid with the green dye was determined by electron microscopy to be an average of 53 ± 30 nm (n = 365) at 0 h and 60 ± 35 nm (n = 303) at 2 h. This was compared with filtered (99m)Tc-sulfur colloid without the green dye, which averaged 71 ± 41 nm (n = 41). Measurements of unfiltered (99m)Tc-sulfur colloid were recorded at 253 ± 192 nm (n = 21) for additional comparisons. The chemical properties and particle size of filtered (99m)Tc-sulfur colloid were not affected by the addition of the green dye; thus, combination of filtered (99m)Tc-sulfur colloid and green dye in the same syringe for administration is suitable.