Evaluation of Zeta-Potential and Particle Size of Technetium ^sup 99m^Tc-Sulfur Colloid Subsequent to the Addition of Lidocaine and Sodium Bicarbonate

The use of (99m)Tc-sulfur colloid lymphoscintigraphy for the determination of lymph flow patterns from a tumor site and localization of the sentinel node has been widely adopted. However, the effects of multiple injections of the radiopharmaceutical can range from mild discomfort to pain. pH-adjusted lidocaine HCl coadministered with (99m)Tc-sulfur colloid presents a risk of introducing instability of the radiopharmaceutical, which could lead to aggregation, possibly impeding the kinetics of lymphatic drainage from the tumor site. In the present study, lidocaine pH-adjusted with 4.2%, 6.3%, or 8.4% sodium bicarbonate was added to the (99m)Tc-sulfur colloid radiopharmaceutical to monitor effects on radiochemical purity, zeta-potential, particle size, and pH. These parameters were then used to evaluate the short-term stability of the preparation. The study revealed that the formulation of lidocaine pH-adjusted with 8.4% sodium bicarbonate added to (99m)Tc-sulfur colloid demonstrated a similar change in zeta-potential (-4.09 +/- 2.90 mV) and particle size (10-330 nm) to that of control filtered (99m)Tc-sulfur colloid (-5.09 +/- 1.68 mV and 11-343 nm, respectively). However, the 4.2% preparation showed a zeta-potential of -3.01 +/- 2.24 mV and a particle size range of 10-351 nm. The pH of the 8.4% buffered preparation, at 7.1, was closer to physiologic pH than was the control, at 6.0. The 6.3% pH-adjusted lidocaine-(99m)Tc-sulfur colloid preparation failed radiochemical purity; thus, it was not included in the analysis. Compared with other (99m)Tc-sulfur colloid test formulations of 4.2% and 6.3% pH-adjusted lidocaine, the 8.4% sodium bicarbonate pH-adjusted lidocaine-(99m)Tc-sulfur colloid preparation, taken as a whole, yielded superior quality-control parameters. This formulation would be an acceptable alternative to the control.