BLEEDING EFFECTS ASSOCIATED WITH HEPARIN contaminants

Clinical use of heparin as an antithrombotic drug Is limited by the risk of excessive bleeding, generally ascribed to the anticoagulant activity of this mucopolysaccharide.

Unexpectedly, some low molecular weight heparins with reduced anticoagulant activity are reported to cause bleeding in clinical and experimental studies. To approach this problem, a number of heparin preparations with various molecular weights were characterized by analysis of their ¹³C-NMR spectra. The bleeding potential of the same heparins was tested by measuring the "template" bleeding time (BT, a method exploring the mechanisms of primary haemostasis) in the rat tail, 15 min after i.v. administration of 0.75 mg/kg b.w. of the drug.

Besides major NMR signals associated with known units of the regular and irregular regions of heparins, some of the preparations display ¹³C-NMR "extra-signals", which have a higher degree of relative intensity in the spectra of samples with higher haemorrhagic potential; indeed, all the samples exceeding in "extrasignals" a conventional intensity level of 2 had at least 70% prolongation of the BT over controls.

These results suggest that specific contaminants, responsible for these¹³C-NMR "extra-signals", may also be responsible for the unusually high bleeding expressed by some heparin preparations. Work is in progress to identify these components and to evaluate which mechanism of primary haemostasis is involved in their haemorrhagic effect.