Technetium-99m ethylene dicysteine: a new renal tubular function agent

Abstract

Technetium-99m ethylene dicysteine (EC), a metabolite of ethylene cysteine dimer (ECD), is a new technetium-labelled renal tubular function tracer introduced as an alternative to ortho-iodohippurate (OIH) and with imaging qualities similar to Tc-99m-mercaptoacetyltriglycine (MAG3). The elimination of Tc-99m-EC is principally via active tubular transport. It is available in lyophilised kit form which can be easily prepared at room temperature, and the compound remains stable for at least 8 h. Both in normal individuals and in patients, plasma clearance of Tc-99m-EC has been reported to be around 0.75 of OIH clearance. Thus there is a very strict correlation between Tc-99m-EC and OIH clearance, and several algorithms are available to estimate OIH clearance from Tc-99m-EC clearance. The renal extraction ratio of Tc-99m-EC is 0.70. The distribution volume of Tc-99m-EC is twice that of Tc-99m-MAG3 (20% of body weight) and slightly higher than that of OIH. The plasma protein-bound fraction of Tc-99m-EC (30%) is significantly lower than that of Tc-99m-MAG3 and OIH. The same applies to red blood cell binding of Tc-99m-EC (5.7%). There is negligible uptake in the liver and intestines. Within 1 h 70% of Tc-99m-EC is excreted in the urine. Tc-99m-EC provides the same scintigraphic information as Tc-99m-MAG3. The lower liver activity makes Tc-99m-EC particularly attractive in patients with renal failure. The Tc-99m-EC clearance can be accurately estimated from a single plasma sample obtained at 54 min after injection. In conclusion, Tc-99m-EC is a suitable renal imaging agent and for some applications is even more attractive than OIH, it provides an index of tubular function and yields high-quality images. The labelling procedure is easy, radiochemical purity is high and the complex is stable for a long time. The extent to which Tc-99m-EC is adopted for clinical use will ultimately depend upon its cost and availability.