Metal-ion speciation in blood plasma as a tool for elucidating the in vivo behaviour of radiopharmaceuticals containing 153Sm and 166Ho

Abstract

In order to elucidate the in vivo behaviour of Sm^III and Ho^III, complex-formation constants for a range of blood plasma metal ions as well as these with the octaanion ethylenediaminetetramethylenephosphonate (edtmp) have been measured at 37 °C and l= 150 mmol dm^–3. The speciation in the absence and presence of edtmp and/or transferrin was calculated by the program ECCLES and is used to explain the apparently anomalous discrepancies in the uptake of the two metals by bone in a baboon model. The computer results predicted the mobilisation of Zn^II and, when tested clinically, it was found that edtmp indeed removes this ion from blood plasma.