Haemodialysis with low MW heparin: dosage requirements for the elimination of extracorporeal fibrin formation.

We have performed a dose ranging study of a low MW heparin, Kabi 2165, during haemodialysis in humans (n = 16) and compared it to a dose of unfractionated commercial heparin that has already been shown to inhibit fibrin formation. Low MW heparin administered as 5000 or 10,000 anti-factor Xa units, s.c., half an hour prior to the initiation of dialysis was unable to prevent fibrin formation in the dialyser circuit. A single bolus injection of 5000 anti-factor Xa units of low MW heparin given i.v. inhibited fibrin formation, as determined by FPA generation, for up to 4 h and permitted dialysis for 6 h. Such a bolus injection may be useful for short frequent dialyses. Infusion of low MW heparin in the same dosage regimen as unfractionated heparin, 5000 anti-factor Xa units bolus plus 1500 anti-factor Xa units/h, resulted in a progressive rise in heparin, caused by its longer half-life of elimination from the circulation, and almost completely suppressed both FPA generation and fibrin clot formation for 6 h dialysis. From these studies we calculate that infusion of this low MW heparin at a dose of approximately 4000 anti-factor Xa units bolus plus 750 anti-factor Xa units/h should be a useful regimen that will be effective in suppressing fibrin formation during prolonged dialysis, and the plasma anti-factor Xa level of low MW heparin may reflect its ability to inhibit fibrin formation, although exactly comparable anti-factor Xa levels of unfractionated commercial heparin and low MW heparins may not have identical inhibitory effects.