Clinical potential of low molecular weight heparins

In recent years there has been an explosion of clinical trials evaluating low molecular weight (LMW) heparin both in the prevention of venous thrombosis and in the treatment of established venous thrombosis. Results to date would indicate that LMW heparin is an effective method of prophylaxis and has a negligible risk of bleeding, provided the anti-factor Xa levels 4-6 h after injection do not exceed 0.2 units/ml. There is suggestive evidence that, if LMW heparin is given in doses which produce anti-factor Xa levels of more than 0.4 units/ml, there is an increased risk of perioperative bleeding in surgical patients. Although three studies have reported that LMW heparin is more effective than standard unfractionated low dose heparin in the prevention of venous thrombosis, further studies evaluating risks and benefits are required. The promising experimental findings that LMW heparin produces less bleeding for equivalent antithrombotic efficacy has yet to be established in man. Results of clinical trials in neurosurgical patients, patients undergoing knee surgery and patients undergoing cardiac surgery may establish whether LMW heparin is advantageous in such patients at very high risk for bleeding. Finally, the early results from randomized trials suggest that LMW heparins are effective in the treatment of established venous thrombosis, but further trials are required.