Radioiodinated fenetylline (captagon) - a new radiopharmaceutical for brain imaging

The purpose of this study was to evaluate radioiodinated fenetylline as a potential brain imaging agent. Thirty Wistar rats were injected with 125I-N-isopropylamphetamine (IMP) and 131I-fenetylline each simultaneously. The animals were sacrificed 5, 10, 15, 30, 60, and 120 min. p. i. The radioactivity content of tissue specimens of different organs was measured in a well counter (% dose/g tissue). After 5/10 min. p. i. fenetylline-uptake in the brain of rats was 1.0/1.3% compared to 1.3/1.9% (IMP). A fast decrease of cerebral fenetylline concentration was established after 30(0.2%) and 60 (0.5%) min. In 2 dogs sequential scintigraphy was performed following the injection of 131I-fenetylline. Three patients underwent brain SPECT after injection of 123I-fenetylline. The canine and human sequential scintigraphy revealed a rapid cerebral uptake suggesting that fenetylline is concentrated in the brain as a function of cerebral blood flow. From our first clinical findings it appears to be likely that the combined use of 123I labeled IMP and fenetylline for SPECT may lead to a more differentiated evaluation of cerebral blood flow and metabolism. (orig.)