Bioanalysis of radioiodine labelled meta-iodobenzylguanidine, its metabolites and free radioiodide in body fluids

Abstract

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