99m technetium labelled heparin: potential value as a tracer of heparin activity in pharmacokinetic and biodistribution studies

Pharmacokinetics and biodistribution of 99m Technetium (sup(99m)Tc) labelled heparin were studied to assess its value as a tracer of heparin kinetics in comparison with unlabelled heparin. In vitro, the stability and labelling efficiency (98%) of the labelled drug were excellent and elution was minimal. In vivo, after I.V. infusion of the drug, there was no difference in the same animal between anticoagulant activity measurements and radioactive countings, both displaying a plasmatic biexponential pattern (T1=2.9 minutes, T2=76 minutes). Biodistribution studies showed primarily liver, spleen and kidney accumulation, with no thyroid uptake. The advantages of this technetium labelling may therefore be used for the heparin drug in various experimental and pathological situations even in humans