Low Molecular Weight Heparin And Postoperative Deep Vein Thrombosis

Abstract

Recent studies have indicated that commercially available heparin is a hetrogenous compound consisting of the molecules of diverse chain length and different molecular weights. Low molecular weight (LMW) heparin has been shown in vitro to possess unique properties which should not only improve its efficacy for preventing post-op DVT but also reduce or eliminate the risk of bleeding complications. The aim of this paper is to report the results of in vivo studies performed to test this hypothesis.Ten healthy volunteers received 5000 USP units of unfractionated heparin (mol. wt. 15,000 daltons) or equivalent amount of LMW heparin (mol. wt. 6000 daltons) subcutaneously. Blood samples were withdrawn 1/2 1, 3 and 5 hours later. These were analysed for anti-thrombotic effect using anti-factor Xa (anti Xa) assay and anticoagulant effect by estimating kaolin cephalin clotting time (KCCT) method. While both the preparations of heparin produced similar response in KCCT assay, LMW heparin was found to be 4 times more active in anti-Xa assay. 30 patients undergoing major abdominal surgery were randomly allocated to receive either 5000 units of unfractionated heparin or equivalent amount of LMW heparin every 12 hourly for 10 days. Blood samples were withdrawn before, during and immediately after surgery and every day during post-op period. These were analysed for anti-thrombin III and heparin concentrations, lipoprotein lipase, fibrinopeptide A, prekallikrein, TxB2 and 6-oxo-PGF1α to assess platelet effect. Significant differences were only observed in lipoprotein lipase and anti-thrombin III concentrations. In ongoing trial 43 patients undergoing major abdominal surgery have received 1500 units of LMW heparin every 12 hourly for 7 post-operative days. Only 1 patient has developed DVT and another wound haematoma. If these results are confirmed in a larger number of patient, then LMW heparin may be ideal drug for prophylaxis against DVT.