Technetium-99m labeling of hippuric and p-amino-hippuric acid in the presence of DTPA: Biological and pharmacokinetic evaluation and comparison with Tc-99m-DTPA

Abstract

Tc-99m-Hipp as a modified Tc-99m-DTpA, and Tc-99m-PAH as a new renal agent are developed. Each veal of lyophilised kit contain hippuric (Hipp) or p-aminohippuric acid (PAH), diethyltriaminepentaacetic acid as calciumtrisodium salt (CaNa(3)DTPA) and stannouschloride (SnCl2. xH(2)O), in molar ratio Hipp/PAH:DTPA = 4:1. They are high radiochemical purity radiopharmaceuticals, with hydrophilic character and low percentage of protein binding. The ITL chromatography and HPLC analyses of these labeled compounds have shown almost identical results as Tc-99m-DTPA, but their biological behavior in rats confirm certain differences. Tc-99m-Hipp is a renal agent clearing by the glomerular system, with better pharmacokinetical parameters than Tc-99m-DTPA: t(1/2(alpha)) = 4.1 min, t(1/2(beta)) = 198.6 min, K-d = 1.2.10(-2)min(-1) and a twofold value for blood clearance (Cl=2.07 ml/min). Tc-99m-PAH is a quite different renal agent, rapidly secreted by kidney as a tubular secretion agent. Its pharmacokinetical parameters: t(1/2(alpha)) = 2.5 min, t(1/2(beta)) = 41.7 min and K-cl = 5.1.10(-4) min(-1) are almost equal to those of Tc-99m-MAG(3), but the blood clearance of Cl = 5.22 ml/min is even higher than that of IOH clearance.