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Tc-99m(Sn)-N-Pyridoxylaminates: A New Series of Hepatobiliary Imaging Agents

Nihon Medi-Physics Co., Ltd., Takarazuka, Japan

Correspondence: For reprints contact: Makoto Kato-Azuma, Research and Development Section, Technical Department, Nihon Medi-Physics Co., Ltd., 4, 2-1, Takatsukasa, Takarazuka, Hyogo Pref., Japan 665.

ABSTRACT

Three derivatives of N-pyridoxylamino acid were synthesized: Tc-99m(Sn)-N-pyridoxylphenylalanine, -N-pyridoxyltryptophan, and -N-pyridoxyl-5-methyltryptophan. The chemical and biologic properties of each complex was found to be quite analogous to those of the corresponding Tc-99m(Sn)pyridoxylideneaminate. In rats, Tc-99m(Sn)-N-pyridoxyl-5-methyltryptophan [Tc-99m(Sn)PHMT] showed rapid blood clearance, fast hepatobiliary transit, low urinary excretion, and no intestinal reabsorption. Over 90% of the dose arrived in the intestine through the liver at 30 min after i.v. administration, whereas only 2% of the dose escaped through the kidneys. In rabbits the gallbladder was clearly visualized within 5 min of injection and no renal or bladder images were noted on any scintiphotos. The BSP (sulfobromophthalein) intervention study revealed that the biliary excretion of Tc-99m(Sn)PHMT is much more resistant than that of Tc-99m(Sn) diethyl-IDA to the intervention of BSP and hence to serum bilirubin. Toxicity studies on PHMT and Sn-PHMT indicated a wide margin of safety for the proposed human dose.