Key result
Direct thrombin inhibitors alter aPTT characteristics, complicating comparisons during overlapping VKA therapy.
Why the study?
Does phenprocoumon affect the aPTT measurement of direct thrombin inhibitors and unfractionated heparin?
Does phenprocoumon affect the aPTT measurement of direct thrombin inhibitors and unfractionated heparin?
Answers are grounded in this paper and cite their sources.
Overlapping therapy with vitamin K antagonists significantly alters aPTT measurements for direct thrombin inhibitors and heparin, complicating the interpretation of anticoagulation intensity.
The activated partial thromboplastin time (aPTT) is currently the most common test used to measure the anticoagulation intensity of heparins and direct thrombin inhibitors (DTIs). Vitamin K antagonists variably affect aPTT reagents. Interactions between heparin and DTIs occur during concurrent therapy. Three DTIs (lepirudin, argatroban, melagatran) and one unfractionated heparin (liquemin) were added to normal plasma (NP) samples (n = 23) and to vitamin K antagonist plasma (VKAP) samples (n = 23) of patients treated with phenprocoumon. Lepirudin and argatroban were added at concentrations from 300 to 3000 ng/ml, melagatran from 30 to 1000 ng/ml, and unfractionated heparin from 0.016 to 0.48 IU/ml. Wave parameters of clotting time and aPTT ratio curves were evaluated by multivariate analysis for inhibitors, aPTT reagents and NP and VKAP samples. Normal ranges resulting from NP samples were 34.5 +/- 1.0 s with Pathromtin SL and 33.9 +/- 0.8 s with Platelin LS. Normal ranges using VKAP were 52.8 +/- 2.6 s (Pathromtin SL) and 44.2 +/- 1.1 s (Platelin LS) (P < 0.0001). Variance analysis showed that inhibitors, plasmas (NP versus VKAP) and reagents influenced the wave characteristics of aPTT (s) (P < 0.0001) and aPTT ratios (P < 0.0001). Distinct statistical differences between aPTT reagents on one hand and normal versus vitamin K antagonist plasma on the other hand make a comparison of reported aPTT results difficult, especially during overlapping therapy with vitamin K antagonists.
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Fenyvesi et al. (2004) studied Patients treated with phenprocoumon (n=46). Direct thrombin inhibitors and unfractionated heparin vs. Normal plasma vs Vitamin K antagonist plasma was evaluated on Wave characteristics of aPTT and aPTT ratios (p=<0.0001). Direct thrombin inhibitors, plasma type, and reagents significantly influenced aPTT characteristics (P<0.0001), complicating aPTT comparisons during overlapping vitamin K antagonist therapy.
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