BIOANALYSIS OF RADIOIODINE LABELED METAIODOBENZYLGUANIDINE, ITS METABOLITES AND FREE RADIOIODIDE IN BODY-FLUIDS

Radioiodinated meta-iodobenzylguanidine ([I-123/I-131]MIBG) is, used f or diagnostic scintigraphy of neural crest tumours (such as neuroblast oma and malignant phaeochromocytoma) and for scintigraphic assessment of cardiac neuronal integrity. Moreover, [I-131]MIBG is also used for radionuclide therapy of neural crest tumours. Part I of this paper pre sents a simple solid phase extraction procedure for the separate quant ification of [I-123/I-131]MIBG and its radiolysis product [I-123/I-131 ]iodide in biological matrices. The method has been validated for whol e blood, plasma, urine and saliva. After intravenous administration of [I-123]MIBG, containing only 2% free [I-123]iodide, to a patient, the [I-123]iodide level-expressed as percentage of total radioactivity in each matrix sample-amounted to: 3% (urine), 5% (blood cells), 20% (wh ole blood), 32% (plasma) and 100% (saliva). Part II describes a sensit ive HPLC procedure, including sample pretreatment, for the determinati on of [I-131]iodide, [I-131]MIBG and three metabolites, including [I-1 31]meta-iodohippuric acid ([I-131]MIHA) and [I-131]meta-iodobenzoic ac id, in urine of patients treated with therapeutic amounts of [I-131]MI BG. The parent drug and its metabolites could be detected in urine for at least 5 days after administration. The procedure was highly reprod ucible for the quantification of [I-131]MIBG and [I-131]MIHA, yielding relative standard deviations of <2% and <5%, respectively.