Renal excretion of meta-iodobenzylguanidine after therapeutic doses in cancer patients and its relation to dose and creatinine clearance.

Iodine-131 radioiodinated meta-iodobenzylguanidine (131I-MIBG) is used for diagnostic scintigraphy and radionuclide therapy of neural crest-derived tumours. In higher doses (up to 80 mg), non-radioactive MIBG is now evaluated for palliation in carcinoid patients. After administration of therapeutic doses of 131I-MIBG (3.7-7.4 GBq, 1.7-5.8 mg MIBG) to patients aged 2-73 years, 53 +/- 8.8%, 69 +/- 7.8% and 83 +/- 7.0% of the dose was cumulatively excreted as MIBG in the urine after 24, 48 and 72 h, respectively. Within the MIBG dose range of 1.7-80.0 mg, a linear relationship was found between the excretion rate over the first 24 h (mg per 24 h) and the dose. In adults, the MIBG excretion rate over the first 24 h (% of dose per 24 h) was shown to be only partially related to the glomerular filtration rate (GFR).