1ST EXPERIENCE IN HEALTHY-VOLUNTEERS WITH TC-99M L,L-ETHYLENEDICYSTEINE, A NEW RENAL IMAGING AGENT

Animal studies have indicated that technetium-99m L,L-ethylenedicysteine (TC-99m-L,L-EC) may be a promising tracer agent for renal function studies. We have performed a paired study with Tc-99m-mercaptoacetyltriglycine (Tc-99m-MAG3) and TC-99m-L,L-EC in six male volunteers. In both cases, iodine-131-labelled o-iodohippurate was co-injected as an internal biological standard. The analog images between 0 and 30 min p.i. were of identical diagnostic value for both tracer agents. The two renograms were similar in all volunteers. The mean 1-h plasma clearance for Tc-99m-MAG3 and 99mTC-L,L-EC was significantly different, respectively 382.9+/-17.1 ml/min per 1.73 m2 versus 460.2+/-47.7 ml/min per 1.73 M2 (P<0.003). The urinary excretion after 30 min p.i. was 69.4%+/-5.6% of the injected dose for Tc-99m-MAG3 versus 66.5%+/-2.5% for Tc-99m-L,L-EC (P>0.05) and after 60 min p.i. respectively 83.1%+/-3.9% versus 79.8%+/-4.3% (P>0.05). Tc-99m-L,L-EC has a very low plasma protein binding (31%+/-6.8%) as compared to Tc-99m-MAG3 (88%+/-5.2%) and a larger volume of distribution. Although the exact mechanism responsible for the high plasma clearance of Tc-99m-L,L-EC is not yet fully known, we conclude that this new agent merits further clinical evaluation in patients to establish its value as a renal radiopharmaceutical.