Decomposition rates of radiopharmaceutical indium chelates in serum

The rates at which six small aminopolycarboxylate chelates of trivalent¹¹¹In and three protein-bound chelates of¹¹¹In deliver indium to the serum protein transferrin have been studied in sterile human serum at pH 7.3, 37°C. Sterically hindered chelates containing a substituent on an ethylene carbon of EDTA decompose with rates in the range 0.03 to 0.11% per day—one to two orders of magnitude slower than other chelates. Only small differences are observed between rates of decomposition for low-molecular-weight chelates and for protein-bound chelates having analogous structures.