Contemporary use of and future roles for heparin in antithrombotic therapy.
Although heparin therapy is an established component of the prevention and treatment of thromboembolic disease, recent advances have resulted in improvements in the clinical use of this agent. Studies have shown that weight-based dosing influences significantly both the time to reach a therapeutic intensity of anticoagulation and the incidence of thromboembolic recurrence. It is now considered the standard of care. A growing understanding of the variability among activated partial thromboplastin time (aPTT) reagents and the influence of these differences on aPTT outcomes has led to the use of reagent-specific therapeutic ranges for heparin monitoring. Many practitioners now choose to adjust the therapeutic range to correspond to heparin serum concentrations of 0.2-0.4 U/mL rather than the more common practice of prolonging aPTT to 1.5-2.5 times the mean normal aPTT. Pharmaceutical companies have developed low molecular weight heparins to minimize adverse effects associated with unfractionated heparin. More specific thrombin inhibitors are also under investigation with the aim of improving clinical outcomes in coronary syndromes now treated with heparin. Low molecular weight heparins or specific thrombin inhibitors are unlikely to replace unfractionated heparin in the near future. Therefore, optimum dosing and appropriate monitoring of heparin are critically important in the management of thromboembolic disease.