Comparative pharmacology of low molecular weight heparins: implications of manufacturing processes on biological effects

Pharmacokinetics of Clivarin a new low molecular weight heparin in healthy volunteers

The antithrombotic activity and pharmacokinetics of Clivarin, a low molecular weight heparin was randomly studied in 10 healthy male volunteers. Doses of 20, 40, 60 and 80 anti F Xa U/kg BW were injected intravenously and subcutaneously in crossover fashion. The heparin concentrations were measured by inhibition of clotting assays (anti IIa and anti Xa activities using amidolytic assays and [dilute] thrombin time). The pharmacokinetic profile of Clivarin is characterized by a linear relationship between dose and absorption, relatively low clearance and a long elimination half-life, and a high anti Xa/anti IIa ratio of 5.3.

Potential use of recombinant hirudin as an anticoagulant in a cardiopulmonary bypass model

Recombinant (r) hirudin is a potent thrombin-specific inhibitor derived from the natural hirudin of the leech (Hirudo medicinalis). We have studied the efficacy of r-hirudin compared with heparin in a canine model of cardiopulmonary bypass operations. Two administration regimens were used for r-hirudin: group 1, 1.0 mg/kg intracardiac bolus then intravenous bolus at 30 minutes (n = 10); and group 2, 1.0 mg/kg intracardiac bolus with 1.25 +/- 0.04 mg.kg-1.h-1 intravenous infusion (n = 8). Group 3 was given an intracardiac bolus of heparin, 1.66 mg/kg (n = 9). Aspiration of blood from the chest cavity revealed no significant difference between the three groups. Measurement of fibrin deposits in the pump line filter revealed higher amounts in the r-hirudin groups (p = 0.02). Decreases in platelets, fibrinogen, and hematocrit due primarily to hemodilution were the same in each group. The bleeding time assay showed less prolongation for r-hirudin than for heparin (p less than 0.001). No antagonist for r-hirudin was used; however, due to its short half-life all coagulation variables returned to baseline within 30 minutes after cardiopulmonary bypass. Because r-hirudin lacks effect on platelets, is a poor immunogen, does not require a plasma cofactor, and may not require an antagonist, it may provide an alternative anticoagulant to heparin in cardiopulmonary bypass. Additional studies are, however, needed to optimize the dose and to evaluate other clinical aspects of r-hirudin.