Formulation of lyophilized single vial kit of N-N-Ethylene-L-Dicysteine (EC) for labeling with 99m Tc. II: Radiochemical and clinical evaluation as a renal tubular agent in comparison with 99m Tc-MAG3.

A Technetium 99m Tc labeled lyophilized single component kit of N-N-ethylene-I-dicysteine (EC) is developed to replace multiple step kit developed by others. The aim of study is to formulate a radionuclide that is easy to prepare, has rapid plasma clearance, produce high quality images and is an affective alternative to radioiodine labeled orthoiodohippurate, which has been remained the physiological 'gold standard' since long time. To achieve this goal, the systematically varied key parameters such as pH, the use of reducing agents, stabilizers and additives are optimized to obtain maximum radiochemical purity and optimum biodistribution in non human and human primates. Various pH levels of EC showed equally good results in animal experiments but only pH 10 was suitable for human use. Dynamic and renal Scintigraphic studies are carried out with 99m Tc-EC at pH 8 in 12 volunteers and at pH 10 in 18 volunteers and compared with 99m Tc-MAG3, Background ratios, renograms, relative renal function and semi quantitative parameters are available in all studies. The background ratios (mean ± SD) at 30th minute are 0229±0.024 and 0.236±0.018 for 99m Tc-EC at pH 10 and 99m Tc-MAG3 respectively. The mean ± standard error of mean (SEM) values of TMAX and time to half activity (T12) for 99m Tc-EC (pH10) are 3.7±0.6 and 7.3±1.0 respectively while for 99m Tc-MAG3, they are 4.0±0.8 and 7.9±1.4 with p values 0.001 and 0.049 respectively. The values of relative renal function (RRF) for 99m Tc-EC and 99m Tc-MAG3 are 50.8±3.11 and 51.2±3.4 respectively with p value of 0.822. The residual activity at 25th minute (A25 / A MAX) and renal uptake are 0. 209±12.67±2.80 for 99m Tc-EC and 0.218±0.035 and 1053±2.98 for 99m Tc-MAG3 (p=0.031 an 0.0003) respectively. The correlation coefficient (R2) for TMAX, T1/2 , A25/AMAX and renal uptake are 0.96, 0.69, 0.93 and 0.85 respectively.