Sources of radiochemical impurities in the 99mTc/S-unprotected MAG3 system

With the aim of obtaining a general insight into the technetium/S-unprotected MAG3 system, the reactions of technetium with the unprotected MAG3 ligand, both at c.a.- and n.c.a.-level, were investigated. Based on a profound knowledge of the reaction route and the TcMAG3 complexes, sources of by-products were identified and eliminated as far as possible. Only a small percentage (< 5%) of intermediate Tc-MAG3 complexes occurs, but this may increase by improper handling of the kit, such as insufficient reaction time. In conclusion, two kinds of impurity may occur in the Tc/MAG3 kit: One is derived from impurities in the ligand (MAG3 disulphide), which can be excluded by careful preparation and storage. The other is caused by insufficient reaction time according to the scheme (Fig. 3) during the labelling procedure. Its content can be minimized by optimization of the reaction time. A reaction time of at least 10 minutes gives about 98% of the renal agent.