• G A Marbet.
• Hämostaselabor DZL, Kantonsspital Basel. gmarbet@uhbs.ch
• Ther Umsch. 2003 Jan 1; 60 (1): 10-3.

AbstractUnfractionated heparin (UH) and low-molecular-weight heparins (LMWH) are antithrombotic drugs covering virtually all indications requiring immediately effective anticoagulation. For prevention and treatment of venous thromboembolism (VTE) UH have mainly been replaced by LMWH due to their practical usefulness (one or two subcutaneous daily doses without laboratory test for dose adjustment) and their more favourable risk-benefit profile. With respect to arterial occlusions this statement is also valid for unstable angina pectoris. The risk to develop heparin-induced thrombocytopenia (HIT) appears to be ten times lower with LMWH. In hospitals the use of UH is reserved for complex cases with high bleeding risk and the necessity to interrupt heparin effects rapidly. Therapeutic doses of UH are monitored by the classical coagulation assays, activated partial thromboplastin time (aPTT) and thrombin time (TT), but also by automated chromogenic tests of anti-factor Xa activity. There are no prospective studies directly comparing the efficiency of these three approaches. Disagreements between tests are not rare in individual cases. However, dosing recommendations for UH treatment of VTE (intravenous bolus of 80 IU/kg, followed by 18 IU/kg/h infusion) and average doses used are concordant. 0.30-0.70 anti-Xa IU/ml are considered as therapeutic range for UF infusion. Higher UH activities required during extracorporeal circulation in heart surgery or during coronary angioplasty are usually guided by bedside ACT (activated clotting time). For LMWH tests of anti-Xa activities may only be necessary during weight adjusted treatment of pregnant women, children, or cases with reduced kidney function (glomerular filtration rate < 30 ml/min.) or increased bleeding risk. Expected anti-Xa activities are 0.5-1.1 IU/ml and 1.0-2.0 IU/ml 4 hours after subcutaneous LMWH for dosing intervals of 12 hours and 24 hours respectively.

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