Human Biodistribution and Radiation Dosimetry of the P-Glycoprotein Radiotracer [(11)C]Metoclopramide

PURPOSE: To assess in healthy volunteers the whole-body distribution and dosimetry of [(11)C]metoclopramide, a new positron emission tomography (PET) tracer to measure P-glycoprotein activity at the blood-brain barrier. PROCEDURES: Ten healthy volunteers (five women, five men) were intravenously injected with 387 ± 49 MBq of [(11)C]metoclopramide after low dose CT scans and were then imaged by whole-body PET scans from head to upper thigh over approximately 70 min. Ten source organs (brain, thyroid gland, right lung, myocardium, liver, gall bladder, left kidney, red bone marrow, muscle and the contents of the urinary bladder) were manually delineated on whole-body images. Absorbed doses were calculated with QDOSE (ABX-CRO) using the integrated IDAC-Dose 2.1 module. RESULTS: The majority of the administered dose of [(11)C]metoclopramide was taken up into the liver followed by urinary excretion and, to a smaller extent, biliary excretion of radioactivity. The mean effective dose of [(11)C]metoclopramide was 1.69 ± 0.26 μSv/MBq for female subjects and 1.55 ± 0.07 μSv/MBq for male subjects. The two organs receiving the highest radiation doses were the urinary bladder (10.81 ± 0.23 μGy/MBq and 8.78 ± 0.89 μGy/MBq) and the liver (6.80 ± 0.78 μGy/MBq and 4.91 ± 0.74 μGy/MBq) for female and male subjects, respectively. CONCLUSIONS: [(11)C]Metoclopramide showed predominantly renal excretion, and is safe and well tolerated in healthy adults. The effective dose of [(11)C]metoclopramide was comparable to other (11)C-labeled PET tracers. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11307-021-01582-4.