Technetium-99m-labeled p-aminohippuric acid analog: a new renal agent: concise communication.

A renal agent labeled with Tc-99m and quantitatively secreted by the tubules has been sought for many years. To meet this need, a PAH analog (PAHIDA), has been synthesized by the coupling of p-aminohippuric acid with nitrilotriacetic acid anhydride, using Sn(II) reduction. This yields a stable complex with Tc-99m at a pH of 5.8. The purity and stability of the Tc-99m complex have been established by ITLC and high performance liquid chromatography (HPLC). Urinary excretions of the Tc-99m PAHIDA and I-131 hippurate, determined in mice and rats at different time intervals, are similar. The new compound is clearly excreted but its total clearance is lower than that of hippurate as a result of high protein binding. Rat urine analysis by ITLC and HPLC suggests that the agent excreted is similar to the complex administered to the animals. The Tc-99m-labeled agent is rapidly excreted in urine with no significant extrarenal pathway, thus providing excellent renal scintigrams in a rabbit model. The Tc-99m PAHIDA contains the R-CO-NH-CH2-COOH grouping, analogous to that in hippurate, and consequently may provide the substrate specificity for renal excretion of this new class of agents labeled with technetium-99m.