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In Vivo Chemistry of Iofetamine HCl Iodine-123 (IMP)

Medi-Physics, Inc., Emeryville, California

Correspondence: For reprints contact: Ronald M. Baldwin, Medi-Physics, Inc., 5855 Christie Ave., Emeryville CA 94608.

ABSTRACT

Application of chemical methods for characterizing the in vivo behavior of iofetamine HCl ¹²³I (IMP) has shed light on the metabolism of iofetamine in animals and humans. A successful technique consists of ethyl acetate extraction of the metabolites from tissue samples acidified with perchloric acid, separation of the mixture by high performance liquid chromatography, and quantitation of the radioactive components with a sensitive scintillation detector. Metabolism of iofetamine HCl ¹²³I proceeds sequentially from the N-isopropyl group on the amphetamine side chain. The first step, dealkylation to the primary amine p-iodoamphetamine (PIA), occurs readily in the brain, lungs, and liver; activity in the brain and lungs consists of only IMP and PIA even 24 hr after administration. The rate-limiting step appears to be deamination to give the transitory intermediate p-iodophenylacetone, which is rapidly degraded to p-iodobenzoic acid and conjugated with glycine in the liver to give the end product of metabolism, p-iodohippuric acid, which is excreted through the kidneys in the urine.