Platelets and Heparin Induced Thrombocytopenia Antibodies Do Not Influence the Inhibitory Activity of Argatroban on Thrombin Generation.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 929-929
Author(s):  
Grigoris T. Gerotziafas ◽  
Marie-Paule Roman ◽  
Elisabeth Verdy ◽  
Mohamed Hatmi ◽  
Meyer M. Samama ◽  
...  
Keyword(s):  
Inhibitory Activity ◽  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
Lag Time ◽  
Thrombin Inhibitor ◽  
Prospective Clinical Study ◽  
Dependent Manner ◽  
Heparin Induced Thrombocytopenia ◽  
Normal Platelet

Abstract Argatroban is a synthetic, reversible, direct thrombin inhibitor (DTI) used in patients with heparin induced thrombocytopenia (HIT). Argatroban as other DTIs prolongs PT, aPTT and ecarin clotting time. Argatroban added in vitro in normal platelet poor plasma (PPP) inhibits tissue factor (TF) triggered thrombin generation (TG) in a concentration dependent manner. We studied the influence of platelets, HIT antibodies and residual heparin, on the inhibitory effect of argatroban on TG. Argatroban (0 to 2 μM) was added in normal platelet rich plasma (PRP) and PPP, in pool PPP from three consecutive HIT patients (HIT-PPP) and in HIT-PRP prepared by mixing normal PRP with HIT-PPP (v/v). HIT-PRP and HIT-PPP were containing residual heparin (0,035 and 0,07 anti-Xa IU/ml respectively). All experiments were repeated 3 times. TG was triggered in the presence of TF (Dade-Behring Innovin; 1/1000 final dilution in plasma) and assessed with Calibrated Automated Thrombinoscope®. TG in PPP was triggered by adding PPP reagent (Thrombogram-Thrombinoscope®). Lag time (LT), time to peak (ttP), peak (P), endogenous thrombin potential (ETP) and mean velocity index (MVI) of thrombin generation were measured. The concentrations of argatroban which prolonged 2-fold the LT and the ttP and which inhibited 50% (IC50) the P, ETP and MVI were calculated. In the presence of low argatroban concentrations (0,1 an 0,2 μM) an artifactual increase of TG was observed. This is probably due to the interference of alpha2macroglobulin-bound thrombin with the fluorogenic substrate (as shown by Hemker’s group for other reversible DTIs). Argatroban at 1 μM inhibited TG by 50% in both normal PRP and PPP. Argatroban at 1 μM induced a 2-fold prolongation of aPTT (Table 1). HIT antibodies did not modify the inhibitory activity of argatroban on TG in HIT-PRP and HIT-PPP. The presence of traces of heparin in plasma from HIT patients had a synergistic effect with argatroban on the inhibition of TG (Table 1). Our in vitro study shows that argatroban at concentration achieved in clinical practice (about 1 μM) induces 50% inhibition of TG. The inhibitory activity of argatroban on TG is not modified by the presence of platelets or HIT antibodies. In contrast, traces of residual heparin in plasma from HIT patients amplify the inhibition of thrombin generation induced by argatroban. This finding has to be confirmed in a prospective clinical study since it implicates an increased vigilance during the switch from heparin to argatroban in acute HIT patients. Table 1. Inhibitory activity of argatroban on thrombin generation. normal PRP normal PPP HIT-PRP (0,03 aXa/ml) HIT-PPP (0,07 aXa/ml) Lag-time x2 0,7 μM 0,7 μM 0,9 μM 0,1 μM ttPeak x2 1 μM 1 μM 1 μM 0,2 μM Peak IC50 1 μM 1 μM 0,7 μM 0,3 μM ETP IC50 1 μM 1 μM 0,7 μM 0,3 μM MRI IC50 1 μM 1 μM 0,5 μM 0,3 μM PTx2 - 1 μM - - aPTT x2 - 1 μM - -

In Vitro Effect of Danaparoid Sodium (Orgaran®) on Thrombin Generation after Minimal Tissue Factor Pathway Activation.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 4151-4151
Author(s):  
Ismail Elalamy ◽  
Anna D. Petropoulou ◽  
Mohamed Hatmi ◽  
Meyer M. Samama ◽  
Grigoris T. Gerotziafas
Keyword(s):  
Molecular Weight ◽  
Tissue Factor ◽  
Thrombin Generation ◽  
Lag Time ◽  
Dependent Manner ◽  
Pathway Activation ◽  
Coagulation Tests ◽  
Vitro Effect ◽  
Routine Coagulation

Abstract Introduction: Orgaran® (Org 10172) is a low molecular weight heparinoid which consists of natural sulphated glycosaminoglycans (heparan, dermatan, chondroitin sulphate). It has a mean molecular weight of approximately 6 kDa (4–10 kDa), an excellent bioavailability following subcutaneous administration and an anti-Xa/anti-IIa activity ratio superior to 22. It is the anticoagulant of choice in patients developping Heparin-Induced Thrombocytopenia (HIT), whereas its’ use is also proposed for surgical thromboprophylaxis. Orgaran® has no effect on routine coagulation tests (aPTT, PT, TT). Thrombin generation test(TG) is a global clotting assay proven to be sensitive to the anticoagulant effect of LMWHs and specific FXa inhibitors (i.e. fondaparinux and BAY-597939). In this in vitro study, we determined the tissue factor (TF)-induced TG inhibition potency of Orgaran® using the Thrombogram-Thrombinoscope® assay. Materials and Methods: TG was assessed after TF pathway activation in Platelet Rich Plasma (PRP) (1.5x105 platelets/μl) using diluted thromboplastin (Dade Innovin®, 1:1000 final dilution). The clotting process is provoked by a physiologically relevant TF concentration. Orgaran® was added to control plasma from 8 healthy volunteers at five different final concentrations (0.2, 0.4, 0.6, 0.8 and 1IU anti-Xa/ml). TG was initiated by adding the triggering solution containing CaCl2 and the fluorogenic substrate. The analyzed TG parameters are the lag time, the maximal concentration of thrombin (Cmax), the time to reach Cmax (Tmax), the TG velocity and the endogenous thrombin potential (ETP). Results: Orgaran® prolonged significantly the lag time and the Tmax at a concentration over 0.40 IU anti-Xa/ml (p<0.05). At the lowest studied concentration (0.20 IU anti-Xa/ml), lag time and Tmax were only prolonged by 12%, whereas their maximal prolongation (around 50%) was observed at 1IU anti-Xa/ml. Furthermore, Orgaran® inhibited ETP, Cmax and TG velocity in an almost linear dose dependent manner. A significant inhibition of ETP, Cmax and TG velocity was obtained at concentrations superior to 0.20 IU anti-Xa/ml. (p<0.05). At the highest studied concentration (1IU anti-Xa/ml) Orgaran® suppressed all TG parameters by about 80% (Table 1). Conclusion: Orgaran® exhibited a significant inhibitory activity of in vitro TG. At concentrations achieved in clinical practice (prophylactic or therapeutic dose), Orgaran® modified in vitro TG profile while it has no effect on routine coagulation tests. Thus, TG assay is a sensitive method for monitoring Orgaran® and this test requires a clinical prospective evaluation. Table 1. Determination of IC20 and IC50 anti-Xa inhibitory concentrations of Orgaran® on TG parameters Lag Time Tmax ETP Cmax Velocity IC: Inhibitory Concentration * or Concentration increasing 20% and 50% the lag time and the Tmax respectively IC 20 (IU/ml) 0.30 0.30 0.18 0.18 0.15 IC 50 (IU/ml) 0.83 >1 0.30 0.50 0.35 1IU anti-Xa/ml 53% 47% 68% 76% 84%

Effect of New Synthetic Heparin Mimetics on Whole Blood Thrombin Generation In Vivo and In Vitro in Rats

2002 ◽  
Vol 87 (02) ◽  
pp. 238-244 ◽  
Author(s):  
J.P. Hérault ◽  
A. Bernat ◽  
C. Gaich ◽  
J.M. Herbert
Keyword(s):  
Venous Thrombosis ◽  
Charge Density ◽  
Whole Blood ◽  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
Lag Time ◽  
Drug Candidate ◽  
Platelet Factor

SummaryThe effect of new heparin mimetics (synthetic oligosaccharides) was studied in vitro with regard to thrombin generation (TG) in rat platelet rich plasma (PRP) and whole blood (WB) and in vivo on stasis-induced venous thrombosis in the rat.TG in PRP and in WB was highly dependent on platelet count and strongly influenced by the haematocrit. The peak of TG appeared to be significantly higher in WB than in PRP whereas the endogenous thrombin potential (ETP) was not significantly different under either condition.The effect of hirudin, the synthetic pentasaccharide SR90107/ Org31540 (SP) and heparin were measured on TG in PRP and WB. We then compared the effect of two new synthetic heparin mimetics (SR121903A and SanOrg123781) with potent and comparable antithrombin (AT) mediated activity against factor Xa and thrombin. These two compounds were made of a pentasaccharide with a high affinity to AT, prolonged at the non-reducing end by an oligosaccharide chain recognised by thrombin. In SR121903A, the charge density and charge distribution was analogous to that of heparin whereas in SanOrg123781 the charges were only located on the last 5 saccharides of the non-reducing end of the molecule. In PRP and in WB, SR121903A acted on the lag time and on the AUC whereas SanOrg123781 inhibited thrombin formation with no effect on the lag time. SanOrg123781 was more potent in inhibiting TG than SR121903A. This difference was due to the structures of the compounds that differed in their ability to be neutralised by platelet factor 4. The antithrombotic effect of the two compounds was examined in a venous thrombosis model in rats. We observed that SanOrg123781 was more active than SR121903A and heparin.Taken together, these results indicate that the activity of oligosaccharides is greatly influenced by the global charge density of the molecule and show that SanOrg123781 is a potent and promising antithrombotic drug candidate.

Abstract WP269: Increased Sensitivity to recombinant Tissue Plasminogen Activator (rtPA)-induced Lysis in vitro of Thrombi Produced in Human Platelet Rich Plasma containing Dabigatran

Stroke ◽  
2013 ◽  
Vol 44 (suppl_1) ◽  
Author(s):  
Joanne van Ryn ◽  
Monika Kink-Eiband ◽  
Davina Fischer ◽  
Johanna Schurer ◽  
Andreas Clemens
Keyword(s):  
Human Platelet ◽  
Synergistic Effects ◽  
Platelet Rich Plasma ◽  
Recombinant Tissue Plasminogen Activator ◽  
Thrombin Inhibitor ◽  
Similar Degree ◽  
Dependent Manner ◽  
Experimental Conditions ◽  
Human Fibrinogen

Dabigatran is a direct thrombin inhibitor approved for the prevention of stroke in patients with atrial fibrillation. It significantly reduced ischemic and hemorrhagic stroke in these patients vs warfarin. However, in patients treated with dabigtran who developed a stroke, there remain unresolved issues regarding thrombolysis therapy, both in terms of timing of lytic treatment to minimize hemorrhage risk and also lytic dose. It is hypothesized that if the fibrin network in a thrombus formed in patients on dabigatran treatment is altered and is less compact, then it may be more sensitive to lysis at lower doses of rtPA. Thrombi were produced in human platelet rich plasma (PRP) in the presence of low conc. of dabigatran (0, 30, 75 ng/ml). PRP was supplemented with 594-Alexa fluorescent labelled human fibrinogen. Thromboplastin (Thromborel ® ) and 200mM CaCl 2 were added and this was incubated at 37°C for 60 min to allow clot formation. Thrombi were removed from PRP and washed twice in saline. They were then added to human plasma from the same subject containing increasing conc. (0-250 IU/ml) of rtPA (Actilyse ® ) and incubated for 2 hrs under continual stirring conditions at 37°C. Lysis was measured as amount of fluorescence released into plasma from the thrombus over 2hrs. Preformed thrombi added to plasma containing only dabigatran underwent no lysis. Lysis of preformed control thrombi (in the absence of dabigatran) occurred in a conc-dependent manner when incubated with rtPA and maximal lysis was achieved with 300 IU/mL. Thus further experiments were performed with ≤250 IU/ml rtPA to look for potential synergistic effects with dabigatran. Clots preformed in PRP containing either 30 or 75 ng/mL dabigatran were more susceptible to rtPA-induced lysis, with maximal lysis achieved with 100 IU/mL rtPA, and ~ 90% lysis was achieved with 50 IU/mL rtPA. These data provide evidence that thrombi preformed in low concentrations of dabigatran appear to be more susceptible to thrombolysis with rtPA than those preformed in the absence of dabigatran, thus lower concentrations of rtPA achieve a similar degree of thrombolysis under these experimental conditions. This may imply that in patients that suffer a stroke while on dabigatran therapy, lower doses of tPA may also be effective.

In-vitro evaluation of anti-factor IXa aptamer on thrombin generation, clotting time, and viscoelastometry

2009 ◽  
Vol 101 (05) ◽  
pp. 827-833 ◽  
Author(s):  
Kenichi Tanaka ◽  
Fania Szlam ◽  
Christopher Rusconi ◽  
Jerrold Levy
Keyword(s):  
Thrombin Generation ◽  
Lag Time ◽  
Clot Formation ◽  
Dependent Manner ◽  
Plasma Samples ◽  
Clotting Time ◽  
Concentration Dependent Manner ◽  
Factor Ixa ◽  
Prolonged Aptt

SummaryThe REG1 system consists of factor IXa inhibitor, RB006, an ap-tamer-based anticoagulant and its antidote, RB007. The optimal use of RB006 can be facilitated by understanding its effect on the formation of thrombin and fibrin, and other standard tests of coagulation. Blood from consented volunteers was drawn into 3.2% citrate (9:1 v/v) and either used immediately or centrifuged to obtain platelet-poor plasma. Increasing concentrations of ap-tamer (6–24 μg/ml) alone or in combination with heparin (0.1 U/ml) or lepirudin (0.2 μg/ml) were added to blood and plasma samples. Activated clotting times (ACT+, low range-ACT), thrombelastometry (ROTEM™) or thrombelastography (TEG®) were performed in recalcified whole blood samples. Thrombin generation, prothrombin time (PT) and activated partial thromboplastin time (aPTT) were performed in plasma samples. To some samples the antidote RB007 was added to neutralise the anticoagulation activity of RB006. In all experiment the ratio of RB006 to RB007 was kept 1:2. RB006 dose-dependently prolonged aPTT and low range-ACT, but, as expected, had no effect on PT. RB006 prolonged the lag time and decreased the peak of Actin-triggered thrombin generation. Thrombin-activated TEG demonstrated that RB006 decreases the rate of clot formation. These effects were potentiated when RB006 was combined with heparin or lepirudin. In all experiments RB007 reversed the effects of RB006 back to baseline. In conclusion, RB006 inhibits thrombin generation and clot formation in a concentration-dependent manner. It is feasible to monitor RB006 and its reversal with RB007 using aPTT, low range-ACT, and thrombin-activated TEG.

Inhibition of In Vitro Thrombin Generation: Another Parameter Reinforcing the LMWH Heterogeneity.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 912-912 ◽  
Author(s):  
Grigoris T. Gerotziafas ◽  
Anna D. Petropoulou ◽  
Mohamed Hatmi ◽  
Meyer M. Samama ◽  
Ismail Elalamy
Keyword(s):  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
In Vitro Study ◽  
Lag Time ◽  
Inhibitory Effect ◽  
Therapeutic Concentration ◽  
Unfractioned Heparin ◽  
Concentration Peak ◽  
Pathway Activation

Abstract Introduction: Low molecular weight heparins (LMWH) are derived from unfractioned heparin (UFH) by depolymerization. Thus, they present biochemical and pharmacological differences and the ratio of anti-Xa/anti-IIa activities varies from one product to another. In this study, we compared in vitro the Thrombin Generation (TG) inhibition potency of various LMWHs and UFH using the Thrombogram-Thrombinoscope® assay. Materials and Methods: TG was assessed after Tissue Factor (TF) pathway activation in Platelet Rich Plasma (PRP) (1.5x105 platelets/μl) using diluted thromboplastin (Dade Innovin®, 1:1000 final dilution). We studied five different LMWHs (Enoxaparin, Dalteparin, Nadroparin, Tinzaparin and Bemiparin), as well as UFH at five different prophylactic and therapeutic anti-Xa final concentrations. These agents were added to control plasma from 14 healthy volunteers with equivalent anti-Xa concentrations. TG was initiated by adding the triggering solution containing CaCl2 and the fluorogenic substrate. The analyzed TG parameters are the lag time, the maximal concentration of thrombin (Cmax), the time to reach Cmax (Tmax), the TG velocity and the endogenous thrombin potential (ETP). Results: Bemiparin had almost no effect on TG, with concentrations below 0.60 IUanti-Xa/ml. Dalteparin, Nadroparin and Enoxaparin showed a similar potency in inhibiting TG at equal anti-Xa concentrations. Tinzaparin proved to be the most active LMWH in inhibiting TG and had a similar potency to UFH. Tinzaparin and UFH, with the lowest anti-Xa/anti-IIa ratio, exerted their inhibitory effect mostly by prolonging lag time and Tmax and by reducing TG velocity, especially at concentration below 0.40 IU anti-Xa/ml. Besides, UFH totally inhibited TG, as expressed by ETP, at a concentration over 0.40 IU anti-Xa/ml. For a given anti-Xa/anti-IIa ratio characterizing each LMWH the IC50 for each parameter was different. The IC50 for the reduction of TG velocity was lower in comparison to the IC50 for the other parameters (Table 1). Conclusion: Our study reinforces the concept of LMWH heterogeneity and the important effect exerted by the additional anti-IIa activity combined with anti-Xa activity. Thus, their characterization can be made through their ability to inhibit TG and not only their anti-Xa/anti-IIa ratio. Nevertheless, in vitro study ignores pharmacokinetic characteristics which are important in clinical practice. Thus, Enoxaparin, at validated prophylactic concentrations (0.20–0.40 IU anti-Xa/ml) had a weak effect on TG parameters, whereas, at peak therapeutic concentrations, it showed an important inhibitory activity similar to Tinzaparin. (Table 2).The use of TG test for the biological monitoring of LMWH requires further evaluation. Table 1. The IC50 for each parameter of TG (anti-Xa IU/ml) Lag time Tmax ETP Cmax Velocity Bemiparin >1 >1 0.98 0.85 0.68 Enoxaparin 0.62 0.58 0.55 0.45 0.38 Nadroparin 0.80 0.75 0.55 0.45 0.38 Dalteparin 0.65 0.65 0.50 0.42 0.38 Tinzaparin 0.35 0.28 0.35 0.25 0.18 UFH 0.05 0.10 0.30 0.25 0.18 Table 2. Effect of Enoxaparin and Tinzaparin on TG at therapeutic concentration peak in vitro Therapeutic Concentration Peak (anti-Xa) Lag Time Tmax ETP Cmax Velocity Enoxaparin 1IU/ml 91% 94% 72% 82% 91% Tinzaparin 0.85 IU/ml >100% >100% 82% 90% 97%

Effect of SR121566A, a Potent GP IIb-IIIa Antagonist on Platelet-mediated Thrombin Generation In Vitro and In Vivo

1998 ◽  
Vol 79 (02) ◽  
pp. 383-388 ◽  
Author(s):  
J. P. Herault ◽  
V. Peyrou ◽  
P. Savi ◽  
A. Bernat ◽  
J. M. Herbert
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Venous Thrombosis ◽  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
Venous Stasis ◽  
Lag Phase ◽  
Dependent Manner

SummaryThe effect of SR121566A, a new non-peptide GP IIb-IIIa antagonist was studied in vitro with regard to thrombin generation in platelet rich plasma and in vivo on stasis-induced venous thrombosis in the rabbit. SR121566A inhibited ADP-, arachidonic acid- and collagen-induced human platelet aggregation with IC50 values of 46 ± 7.5, 56 ± 6 and 42 ± 3 nM, respectively. In the same experimental conditions, SR121566A strongly inhibited thrombin generation triggered by low concentrations of tissue factor. SR121566A reduced in a dose-dependent manner both the area under the curve and the thrombin peak concentration but did not affect the lag phase (defined as the time until 10 nM thrombin was generated). Aspirin (100 µg/ml) did not affect thrombin generation.One hour after intravenous administration to rabbits, SR121566A exhibited a potent ex vivo inhibitory effect against ADP-, arachidonic acid- and collagen-induced platelet aggregation. The ID50 were 0.6 ± 0.25, 0.7 ± 0.08 and 0.13 ± 0.08 mg/kg, respectively. The ability of aspirin and SR121566A to affect venous stasis was determined in a stasis-induced venous thrombosis model in rabbits under high and low thrombogenic challenges. While aspirin was ineffective in both conditions, SR121566A significantly inhibited thrombus formation under low thrombogenic challenge demonstrating for the first time that a potent non-peptide platelet GP IIb-IIIa antagonist inhibits thrombin generation in vivo and exhibits a strong antithrombotic effect with regard to stasis-induced venous thrombosis. These results therefore confirm the existence of a close relationship between platelet activation and thrombin generation leading to blood coagulation but also emphasise the key role of platelets in the development of venous thrombosis, most likely through activation of the GP IIb-IIIa complex.

Effects of argatroban, danaparoid, and fondaparinux on trombin generation in heparin-induced thrombocytopenia

2013 ◽  
Vol 109 (03) ◽  
pp. 504-509 ◽  
Author(s):  
Marion Combe ◽  
Michèle Piot ◽  
Céline Chapelle ◽  
Majid Akrour ◽  
Bernard Tardy ◽  
...  
Keyword(s):  
Clinical Studies ◽  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
Study Objective ◽  
Heparin Induced Thrombocytopenia ◽  
Thrombin Generation Assay ◽  
Vitro Effect ◽  
Vitro Data ◽  
In Vitro Data

SummaryThere is no in vitro data on the comparison of the effects of danaparoid, argatroban and fondaparinux on thrombin generation in patients with heparin-induced thrombocytopenia. It was the study objective to compare the in vitro anticoagulant potential of argatroban, danaparoid and fondaparinux using a thrombin generation assay TGA on a mixture of control platelet-rich plasma (PRP) and HIT patient platelet-poor plasma (PPP). The plasma of seven patients with a clear HIT diagnosed at our institution was selected. Mixtures of donor PRP and patient PPP were incubated with unfractionated heparin 0.2 U.mL-1, argatroban at 600 ng.mL-1, argatroban at 400 ng.mL-1, danaparoid at 0.65 IU.mL-1 and fondaparinux at 1 [uni03BC]g.mL-1. Thrombin generation was assessed by calibrated thrombinography. The percentage of inhibition of the endogenous thrombin potential observed with argatroban at 600 ng.mL-1 was statistically significantly higher compared with those observed with fondaparinux (median: 53.6% vs. 3.9%; p = 0.031) but not compared with argatroban at 400 ng.mL-1 and danaparoid. The percentage of inhibition of the thrombin peak observed with argatroban at 600 ng.mL-1 was statistically significantly higher compared with those observed with danaparoid (median: 71.2 vs. 56.8; p = 0.031) and fondaparinux (mean: 71.2 vs. 30; p = 0.031) but not with argatroban at 400 ng.mL-1. In conclusion, the in vitro effect of argatroban and danaparoid on thrombin generation seems to corroborate the results of clinical studies of these drugs in the treatment of HIT in term of efficiency. Fondaparinux showed a very small effect on thrombin generation evaluated by calibrated thrombinography.

Abstract 264: Differential Profiles of Thrombin Inhibitors (Dabigatran, Hirudin, Bivalirudin and Heparin) in the Thrombin Generation Assay (TGA) and Thromboelastography (TEG) in Vitro

2012 ◽  
Vol 32 (suppl_1) ◽  
Author(s):  
Yiming Xu ◽  
Weizhen Wu ◽  
Andrew S Plump ◽  
Madhu Chintala ◽  
Martin L Ogletree ◽  
...  
Keyword(s):  
Thrombin Generation ◽  
Rank Order ◽  
Therapeutic Index ◽  
Lag Time ◽  
Thrombin Inhibitors ◽  
Bleeding Complications ◽  
Thrombin Inhibitor ◽  
Direct Thrombin Inhibitors ◽  
Therapeutic Benefits

Thrombin is a central enzyme in haemostasis and thrombosis, and a proven target for anticoagulant therapies. Different classes of thrombin inhibitors, while exerting therapeutic benefits in most clinical trials, have different indications, dosing regimens, and bleeding complications. To gain more insight into the underlying mechanisms for their differential clinical profiles, we compared four marketed and representative agents, including dabigatran, hirudin, bivalirudin (direct thrombin inhibitors, DTIs), and heparin (an indirect thrombin inhibitor), in two in vitro spike-in assays with concentration titrations covering their therapeutic ranges. The two assays were the Thrombinoscope TGA with plasma, triggered by low tissue factor (1 nM TF), and TEG with whole blood, triggered by 1:8000 Recombiplastin (equivalent to low TF), with or without a threshold level of tPA to induce fibrinolysis. In TGA, the largest effect was prolongation of lag time, with the potency of the three DTIs rank-ordered as hirudin>dabigatran>bivalirudin; regarding peak, slope, and ETP, while complete inhibition was achieved with 1-2 μM dabigatran or hirudin, bivalirudin had no effect even at 4 μM, possibly due to its short half life in plasma. In TEG, the three DTIs prolonged clotting time (R) in the same rank order as TGA; for clot strength (MA), while all four agents reduced MA in synergy with tPA, only hirudin reduced MA without tPA, likely due to its highest potency. With tPA-induced fibrinolytic activity (Ly30), dabigatran and bivalirudin enhanced Ly30 (dabigatran>bivalirudin), but hirudin and heparin did not. This contrast might involve differential access to clot-bound thrombin. Heparin had a steep dose-response curve for both lag time in TGA and R in TEG, which is in line with its very narrow therapeutic index. All three DTIs, but not heparin, displayed the previously reported paradoxical increase in peak and slope in TGA in the low concentration range, suggesting this is indeed a class effect of DTI. In summary, our observations highlight the distinct features of each agent in thrombin generation, coagulation, and fibrinolysis. These results in combination with known clinical properties are informative on efforts to define the optimal profiles of new anticoagulants.

HEPARIN-INDUCED THROMBOCYTOPENIA: IN VITRO STUDIES WITH LOW MOLECULAR WEIGHT HEPARINOID, ORG 10172

1987 ◽  
Author(s):  
B H Chong ◽  
F Ismail ◽  
J Cade ◽  
A S Gallus ◽  
S Gordon ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Inhibitory Effect ◽  
Heparin Therapy ◽  
Cross Reactivity ◽  
Low Molecular Weight ◽  
Heparin Induced Thrombocytopenia ◽  
Normal Platelet

Heparin-induced thrombocytopenia (HIT), an adverse effect of heparin therapy, may be associated with serious thrombosis resulting in severe disability or death. An IgG heparin-dependent antibody may be demonstrated in HIT by platelet aggregation studies with patient serum/plasma and standard (s) heparin. A recent study showed high cross-reactivity of the antibody with low molecular weight (LMW) heparins as most of the 22 patient sera tested gave a positive reaction with various LMW heparins including CY222, CY216, PK10169 and Kabi 2165 (Messmore HL et al, Blood 64(5), 1984 suppl). However, cross-reactivity rate with Org 10172, a LMW heparinoid which has strong anti-Xa but negligible antithrombin activity, is unknown. We tested the plasma of 17 patients with HIT for cross-reactivity with Org 10172. Although all 17 patient plasmas reacted positively with s.heparin (0.2 1.0 IU/ml), only 3 patient plasmas gave a positive but weaker reaction with Org 10172 (0.2-1.0 IU/ml).Further studies were performed to investigate the effect of adding Org 10172 (0.2 to 2.0 anti-Xa U/ml) to a reaction mixture of normal platelet-rich plasma, patient plasma and s.heparin (0.2 IU/ml). With 7 patient plasmas which showed no cross-reactivity with Org 10172, the antibody-induced platelet aggregation was inhibited when the concentration of Org 10172 exceeded 0.5 to 1.0 anti-Xa U/ml. When the study was repeated with other s.heparin concentrations (0.05, 0.1, 0.4 IU/ml), this inhibitory effect was again present provided the ratio of Org 10172 concentration (anti-Xa U/ml) to heparin concentration (IU/ml) exceeds 2.5 to 5. However, this inhibitory effect was not observed with the 3 patient plasmas which showed cross-reactivity with the heparinoid whqp. the same concentrations of Org 10172 were added. This inhibitory effect appeared to be specific for platelet aggregation induced by the heparin-dependent antibody as Org 10172 (<10 anti-Xa U/ml) did not affect platelet aggregation induced by collagen (2 ug/ml) and ADP (2.5 uM). These findings together with our experience of 3 cases of HIT successfully treated with Org 10172 suggest that this LMW heparinoid may be a useful drug for the treatment of HIT.

Combined Thrombin and Platelet Inhibition Treatment for HIT Patients

1999 ◽  
Vol 19 (03) ◽  
pp. 128-133 ◽  
Author(s):  
B.E. Lewis ◽  
W. P. Jeske ◽  
F. Leya ◽  
Diane Wallis ◽  
M. Bakhos ◽  
...  
Keyword(s):  
Standard Dose ◽  
Combined Therapy ◽  
Platelet Inhibition ◽  
Thrombin Inhibitors ◽  
Thrombin Inhibitor ◽  
Heparin Induced Thrombocytopenia ◽  
Acute Thrombosis ◽  
Anti Platelet Drug ◽  
Receptor Inhibitor

SummaryDespite the use of potent anticoagulants such as r-hirudin and argatroban, the morbidity and mortality in heparin-induced thrombocytopenia (HIT) patients remains unacceptable. Data from our in vitro investigations show that thrombin inhibitors do not block platelet activation induced by heparin antibodies and heparin but that GPIIb/IIIa receptor inhibitors do block this process. We have treated four HIT positive patients with a combined therapy of thrombin inhibitor and GPIIb/IIIa receptor inhibitor when treatment with thrombin inhibitor alone failed to alleviate acute thrombosis. Combination therapies included r-hirudin (Refludan®) with tirofiban (Aggrastat®) and argatroban (Novastan®) with abciximab (ReoPro®). A reduced dose of the thrombin inhibitor was used with the standard dose of the anti-platelet drug. In all cases, there was no overt bleeding which required intervention, and all patients exhibited clinical improvement or full recovery. These case studies suggest that treatment of active thrombosis in HIT patients with adjunct GPIIb/IIIa receptor inhibitor therapy may be more effective than thrombin inhibitor treatment alone.

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