[Phase 1 clinical study of 123I-iomazenil: a new probe to evaluate central-type benzodiazepine receptor with SPECT].

A Phase 1 clinical study of 123I-iomazenil (IMZ), a new radiopharmaceutical developed for evaluation of central-type benzodiazepine receptor (BZR) with SPECT, was performed to examine its safety and biodistribution in six healthy volunteers. The brain uptake of 123I-IMZ reached a maximum value of 11.7 +/- 1.6% of the injected dose at 10-20 min after i.v. administration, and then decreased slowly. The regional tracer distribution immediately after injection (0-10 min) was considered to be a reflection of the cerebral blood flow. From 2 to 3 hours post-injection, washout of the radioactivity from the deep gray matter was observed, resulting in the distribution reflecting the reported distribution of BZR. No significant accumulation was seen in any organ other than the brain. The estimated absorbed dose of 123I-IMZ calculated by the MIRD method was comparable to that of 123I-N-isopropyl-p-iodoamphetamine. Neither adverse reactions nor abnormal clinical laboratory findings due to the drug administration were observed. These results suggest that 123I-IMZ is a safe and promising agent for evaluating the function of central-type BZR.