Indium-111 DTPA-Heparin: Radiolabeling, Pharmacokinetics, and Biodistribution Following Intravenous Administration in Rat and Rabbit

Abstract Heparin was coupled to DTPA using the bicyclic anhydride and labeled with Indium-111. This resulted in a radiochemically pure preparation (greater than 95% activity in one peak) as determined by high pressure liquid radiochromatography and did not affect the anticoagulant properties of heparin. Biodistribution in the rat at 1, 20, and 60 minutes after intravenous injection showed rapid blood clearance with uptake in the liver followed by bone and kidney when expressed as percent injected total dose per organ and liver followed by kidney and spleen when expressed as percent injected total dose per gram. Blood elimination in the rabbit was 18.5 minutes which decreased to 7.5 minutes when followed by the injection of protamine. Radioactivity cleared from the liver and lungs as a single exponential with a half-time of 30 minutes, but there was very rapid increase of radioactivity in the lungs, peaking at 1–2 minutes, following the injection of protamine. Indium-111 DTPA-heparin may be used to study in vivo pharmacokinetics and biodistribution of heparin.