Activated Clotting Time as an Appropriate Test to Compare Heparin and Direct Thrombin Inhibitors Such as Hirudin or Ro 46-6240 in Experimental Arterial Thrombosis

Abstract Funding Acknowledgements Type of funding sources: None. Background Direct thrombin inhibitors (DTIs) unlike factor Xa-inhibitors (Xa-inhibitors) is associated with fewer bleeding complications than warfarin in patients who had catheter ablation (CA) for atrial fibrillation (AF). However, the mechanisms remains unclear, and activated clotting time (ACT) is used to control heparin-dose for thromboembolic prevention during CA. Methods: We retrospectively studied 543 patients taking direct oral anticoagulant (DOAC) who underwent CA for AF (375 males, age 67 ± 10, 251 non-paroxysmal AF, 142 DTIs). Patients with off-label usage of DOAC were excluded. ACT was measured before (Pre-ACT) and after (post-ACT) initial heparin administration (3000U + 100U/kg), and total heparin-dose was evaluated. Results: Pre-ACT and post-ACT were extended in patients with DTIs (150 ± 21 vs 123 ± 15; P < 0.0001 and 322 ± 39 vs 309 ± 42 sec; P = 0.0013). Patients with Xa-inhibitors required higher total heparin-dose (199 ± 43 vs 175 ± 34 U/kg; P < 0.0001). During and after CA, none had thromboembolic events and 14 patients (3 DTIs, 11 Xa-inhibitor) showed bleeding events (Figure). Conclusions: ACT is extended in patients taking DTIs. Xa-inhibitors might have anticoagulant effects which are not reflected in ACT. Abstract Figure.

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The uncalibrated prothrombinase-induced clotting time test

Hämostaseologie ◽

10.1055/s-0037-1619058 ◽

2010 ◽

Vol 30 (04) ◽

pp. 212-216 ◽

Cited By ~ 9

Author(s):

R. Jovic ◽

M. Hollenstein ◽

P. Degiacomi ◽

M. Gautschi ◽

A. Ferrández ◽

...

Keyword(s):

Factor Xa ◽

Heparin Therapy ◽

Thrombin Inhibitors ◽

Coagulation Cascade ◽

Diagnostic Tools ◽

Direct Thrombin Inhibitors ◽

Functional Assay ◽

Clotting Time ◽

Coagulation Time ◽

Time Test

SummaryThe activated partial thromboplastin time test (aPTT) represents one of the most commonly used diagnostic tools in order to monitor patients undergoing heparin therapy. Expression of aPTT coagulation time in seconds represents common practice in order to evaluate the integrity of the coagulation cascade. The prolongation of the aPTT thus can indicate whether or not the heparin level is likely to be within therapeutic range. Unfortunately aPTT results are highly variable depending on patient properties, manufacturer, different reagents and instruments among others but most importantly aPTT’s dose response curve to heparin often lacks linearity. Furthermore, aPTT assays are insensitive to drugs such as, for example, low molecular weight heparin (LMWH) and direct factor Xa (FXa) inhibitors among others. On the other hand, the protrombinase-induced clotting time assay (PiCT®) has been show to be a reliable functional assay sensitive to all heparinoids as well as direct thrombin inhibitors (DTIs). So far, the commercially available PiCT assay (Pefakit®-PiCT®, DSM Nutritional Products Ltd. Branch Pentapharm, Basel, Switzerland) is designed to express results in terms of units with the help of specific calibrators, while aPTT results are most commonly expressed as coagulation time in seconds. In this report, we describe the results of a pilot study indicating that the Pefakit PiCT UC assay is superior to the aPTT for the efficient monitoring of patients undergoing UFH therapy; it is also suitable to determine and quantitate the effect of LMWH therapy. This indicates a distinct benefit when using this new approach over the use of aPPT for heparin monitoring.

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Determination of direct thrombin inhibitors like hirudin in plasma - Comparison of the Ecarin Chromogenic Assay (ECA) with the Ecarin Clotting Time (ECT) and the Activated Partial Thromboplastin Time (APTT)

Journal of Thrombosis and Haemostasis ◽

10.1111/j.1538-7836.2003.tb05302.x ◽

2003 ◽

Vol 1 ◽

pp. P1908-P1908

Author(s):

U. Lange ◽

A. Olschewski ◽

A. Heider ◽

G. Nowak ◽

E. Bucha

Keyword(s):

Partial Thromboplastin Time ◽

Activated Partial Thromboplastin Time ◽

Thrombin Inhibitors ◽

Direct Thrombin Inhibitors ◽

Clotting Time ◽

Chromogenic Assay ◽

Ecarin Clotting Time

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The Ecarin Clotting Time, a Universal Method to Quantify Direct Thrombin Inhibitors

Pathophysiology of Haemostasis and Thrombosis ◽

10.1159/000081505 ◽

2003 ◽

Vol 33 (4) ◽

pp. 173-183 ◽

Cited By ~ 95

Author(s):

Götz Nowak

Keyword(s):

Thrombin Inhibitors ◽

Direct Thrombin Inhibitors ◽

Universal Method ◽

Clotting Time ◽

Ecarin Clotting Time

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Assessment of Heparins, Heparinoids and Direct Thrombin Inhibitors Using a New FXa-and RVV-V-Based Assay.

Blood ◽

10.1182/blood.v104.11.1856.1856 ◽

2004 ◽

Vol 104 (11) ◽

pp. 1856-1856

Author(s):

Andreas Calatzis ◽

Armin J. Reininger ◽

Michael Spannagl

Keyword(s):

Molecular Weight ◽

Healthy Volunteers ◽

Dose Response ◽

Low Molecular Weight Heparin ◽

Thrombin Inhibitors ◽

Direct Thrombin Inhibitors ◽

Low Molecular Weight ◽

Additive Effects ◽

Clotting Time ◽

Linear Dose

Abstract UFH and direct thrombin inhibitors are usually monitored using the activated partial thromboplastin time (aPTT), which has many known limitations. These include non-linear-dose response-relationships as well as a high variability among different reagents. In addition the aPTT has a low sensitivity towards low molecular weight heparin (LMWH). Newer methods such as chromogenic substrate analysis, ecarin clotting time or the Heptest assay have provided improved sensitivity and specificity, but still have not reached broad application in routine or emergency laboratories. The performance of a new universal monitoring method (Pefakit® PiCT®, Pentapharm, Basel) in detecting anticoagulant effects of anti-Xa and / or arti-IIa agents was evaluated. Methods: Measurements were performed by addition of platelet poor plasma to a reagent containing a combination of FXa, RVV-V (FV activating snake venom) and phospholipids. After 180 s the samples were recalcified and the clotting time was recorded. Plasma samples from 30 healthy blood donors and 50 patients receiving low molecular weight heparin were analyzed. To evaluate the assay precision 30 samples were analyzed in triplicate. Plasma pools from healthy volunteers and patients under oral anticoagulant treatment were spiked with unfractionated heparin, low molecular weight heparin, argatroban and pentasaccharide. Results: PiCT® clotting times of the healthy volunteers were 20.6 ± 1.2 sec. Clotting times of the patient samples ranged 29–195 sec. Correlation of anti-Xa activity to PiCT® clotting times was good (r=0.94). The mean variation coefficient of the repeated determinations was 2.6%. Addition of LMWH, UFH or Argatroban to normal plasma showed a steep increase and almost linear dose-response of the PiCT clotting times. Addition of pentasaccharide showed a non-linear dose-response with lesser increase of clotting times at concentrations above 0.75 μg/ml plasma. The addition of LMWH or UFH to plasma of patients under warfarin therapy showed moderate additive effects when compared to normal plasma, while stronger additive effects of warfarin and heparin therapy were found for argatroban. Conclusion: The prothrombinase induced clotting test (PiCT ®) is a new clotting assay, which sensitively assesses LMWH, UFH and direct thrombin inhibitors with almost linear dose-response-relationships. The results revealed a wide measuring range which allows for assessment of prophylactic, therapeutic and supratherapeutic doses of these compounds. As a clotting test with pipetting volumes and an incubation regimen identical with the aPTT, the test can be used in routine or emergency laboratories, thus facilitating 24-hour availability of the method with short turn-around times. Allowing the assessment of heparins, heparinoids as well as direct thrombin inhibitor therapy with one method may simplify their management in clinical practice.

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Transition from argatroban to oral anticoagulation with phenprocoumon or acenocoumarol: effects on prothrombin time, activated partial thromboplastin time, and Ecarin Clotting Time

Thrombosis and Haemostasis ◽

10.1160/th03-12-0794 ◽

2004 ◽

Vol 91 (06) ◽

pp. 1137-1145 ◽

Cited By ~ 43

Author(s):

Jochen Graff ◽

Ute Klinkhardt ◽

Nils von Hentig ◽

Jeanine Walenga ◽

Hikari Watanabe ◽

...

Keyword(s):

Prothrombin Time ◽

Partial Thromboplastin Time ◽

Combined Treatment ◽

Activated Partial Thromboplastin Time ◽

Thrombin Inhibitors ◽

Thrombin Inhibitor ◽

Direct Thrombin Inhibitors ◽

Sensitivity Index ◽

Clotting Time ◽

Ecarin Clotting Time

SummaryTreatment with the direct thrombin inhibitor argatroban (ARG) is often followed by vitamin K-antagonist treatment (VKA). Phenprocoumon (PC) and acenocoumarol (AC) are frequently used in Europe. The standard monitoring test for VKA, prothrombin time (PT), is prolonged by direct thrombin inhibitors. Therefore the International Normalized Ratio (INR) obtained during combined treatment does not reflect the true effect of the VKA. A similar interference of the VKA on the activated partial thromboplastin time (aPTT), a monitoring assay for direct thrombin inhibitors, can occur. In 39 healthy volunteers the effect of ARG alone or combined with PC or AC on PT, INR, aPTT, and Ecarin Clotting Time (ECT) was investigated. 6 groups each of 6-8 volunteers received a 5-hour infusion of either 1.0, 2.0 or 3.0 µg/kg/min ARG (days 1, 3, 4 and 5) before initiation of either PC or AC (day 1) and during continued VKA dosing (target INR 2-3). A linear relationship (INR ARG+VKA = intercept + slope * INR VKA alone) was observed between the INR measured “on” and “off” ARG.The slope depended on the argatroban dose and on the International Sensitivity Index (ISI) of the PT reagent, the steepest slope (i.e., the largest difference between INR ARG+VKA and INR VKA alone) was seen with the highest ARG dose and the PT reagent with an ISI of 2.13.There was a close correlation between plasma levels of ARG and aPTT or ECT. Under VKA the ARG-aPTT relationship indicated an increased sensitivity of the aPTT to ARG, VKA treatment had no effect on the prolongation of the ECT induced by argatroban. In conclusion, ARG at doses up to 2 µg/kg/min can be discontinued at an INR of 4.0 on combined therapy with VKA, as this would correspond to an INR between 2.2 and 3.7 for the VKA. If it is necessary to monitor ARG in the critical transition period, the ECT which is not influenced by VKA can be used as an alternative to the aPTT.

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Differences in the clinically effective molar concentrations of four direct thrombin inhibitors explain their variable prothrombin time prolongation

Thrombosis and Haemostasis ◽

10.1160/th05-03-0154 ◽

2005 ◽

Vol 94 (11) ◽

pp. 958-964 ◽

Cited By ~ 106

Author(s):

Andreas Greinacher ◽

Sharon Craven ◽

Lori Dewar ◽

Jo-Ann Sheppard ◽

Frederick Ofosu ◽

...

Keyword(s):

Prothrombin Time ◽

Clinical Effect ◽

Rank Order ◽

Plasma Concentrations ◽

Factor Xa ◽

High Plasma ◽

Thrombin Inhibitors ◽

Direct Thrombin Inhibitors ◽

Clotting Time ◽

Bovine Plasma

SummaryFour direct thrombin inhibitors (DTIs), lepirudin, bivalirudin, argatroban, and melagatran, differ in their ability to prolong the prothrombin time (PT). Paradoxically, the DTI in clinical use with the lowest affinity for thrombin (argatroban) causes the greatest PT prolongation. We compared the effects of these DTIs on various clotting assays and on inhibition of human and bovine factor Xa (FXa). On a mole-for-mole basis, lepirudin was most able to prolong the PT, activated partial thromboplastin time (APTT), and thrombin clotting time (TCT), whereas argatroban had the least effect. At concentrations that doubled the APTT (argatroban, 1 μmol/l; melagatran, 0.5 μmol/l; bivalirudin, 0.25 μmol/l; lepirudin, 0.06 μmol/l), the rank order for PT prolongation was: argatroban > melagatran > bivalirudin > lepirudin. Although the Ki’s associated with inhibition of human FXa by melagatran (1.4 μmol/l) and argatroban (3.2 μmol/l) approach their therapeutic concentrations, inhibition of FXa did not appear to be a major contributor to PT prolongation, since argatroban also prolonged the PT of bovine plasma (despite a Ki for bovine FXa of 2,600 μmol/l). Only melagatran inhibited prothrombinase-bound FXa. We conclude that the differing effects of the DTIs on PT prolongation are primarily driven by their respective molar plasma concentrations required for clinical effect. DTIs with a relatively low affinity for thrombin require high plasma concentrations to double the APTT; these higher plasma concentrations, in turn, quench more of the thrombin generated in the PT, thereby more greatly prolonging the PT.

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