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

99mTc-Hipp as a modified 99mTc-DTPA, and 99mTc-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 (CaNa3DTPA) and stannouschloride (SnCl2 x xH2O), 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 99mTc-DTPA, but their biological behavior in rats confirm differences. 99mTc-Hipp is a renal agent clearing by the glomerular system, with better pharmacokinetical parameters than 99mTc-DTPA:t1/2(α) = 4.1 min, t1/2(β) = 198.6 min, Kcl = 1.2 x 10-2 min-1 and a twofold value for blood clearance (Cl = 2.07 ml/min). 99mTc-PAH is a quite different renal agent, rapidly secreted by kidney as a tubular secretion agent. Its pharmacokinetical parameters: t1/2(α) = 2.5 min, t1/2(β) = 41.7 min and Kcl = 5.1 x 10-4 min-1 are almost equal to those of 99mTc-MAG3, but the blood clearance of Cl = 5.22 ml/min is higher than that of IOH clearance. (author)