BIODISTRIBUTION AND DOSIMETRY OF CARBON-11-METHOXYPROGABIDIC ACID, A POSSIBLE LIGAND FOR GABA-RECEPTORS IN THE BRAIN

Carbon-11-methoxyprogabidic acid (C-11-MPGA) was recently synthetized as a possible ligand for PET studies of gamma-aminobutyric acid (GABA) receptors in the brain, The data for human absorbed dose estimates ar e calculated based on the biodistribution of C-11-MPGA in mice and hum ans, Methods: Eighteen mice were killed at preset time intervals after an intravenous bolus injection of 3.7 MBq (100 mu Ci) C-11-MPGA. Time -activity curves were reconstructed for several organs, Three healthy men each had whole-body PET scans after an intravenous bolus injection of 37 MBq (1 mCi) to determine activity in the critical organs. Anima l data were fitted into these human findings to calculate residence ti mes, and the MIRDOSE 3 protocol was used to calculate the radiation ab sorbed dose, Results: Animal studies demonstrated a rapid distribution of C-11-MPGA in several organs, The highest activity was detected in the intestines, liver and kidneys, Brain activity was low throughout c ompared to these organs, The human whole-body study yielded similar re sults, with the intestines, liver and kidneys showing the highest acti vity, The estimated dose to the urinary bladder compartment turned out to be significant, The mean effective dose was 4.8 mu Sv/MBq (s.d. = 0.5 mu Sv/MBq). Conclusion: PET studies using 185 MBq (5 mCi) C-11-MPG A are within the International Commission on Radiological Protection r isk Category II for healthy volunteers.