Heparins are commonly used agents in the prevention and treatment of thromboembolic disease. Resistance to heparins is determined by the pharmacokinetic and the pharmacodynamic profile of each preparation. Various conditions, such as overweight, thrombocythemia, extensive thrombi, amino acid infusions, antithrombin deficiency, anti-heparin/platelet factor 4-antibod-ies can induce resistance to heparins, detected as inability to achieve therapeutic intensity of anticoagulation by the usual monitoring assays. Skin reactions might be possible causes of resistance, but no systematic data are available on that. Various types of hypersensitivity reactions to heparins have been reported, such as delayed type IV, immediate type I, heparin-antibodies, peripheral eosinophilia. Resistance can be overcome in most of the cases by proper dose adjustment. An alternative anticoagulant, considering cross-reactivity is the treatment of choice against hypersensitivity reactions.
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