Coagulation parameters in patients receiving dabigatran etexilate or rivaroxaban: Two observational studies in patients undergoing total hip or total knee replacement

Measuring Oral Direct Inhibitors (ODIs) of thrombin and factor Xa: A recommendation from the Subcommittee on Control of Anticoagulation of the Scientific and Standardisation Committee of the International Society on Thrombosis and Haemostasis

Oral direct inhibitors (ODIs) of thrombin and factor Xa are now approved as anticoagulant drugs. The first two drugs to complete phase III clinical trials for thromboprophylaxis in orthopaedic surgery and treatment of patients with atrial fibrillation or venous thromboembolism were dabigatran and rivaroxaban. These small molecules are given at fixed dose with no requirement for monitoring as pharmacokinetic and pharmacodynamic responses are reliably predicted in patients with adequate renal function who are not taking other interacting drugs. However, there will be clinical circumstances in specific patients when measurement of the anticoagulant effect of an ODI will be required. © 2013 International Society on Thrombosis and Haemostasis.

Antithrombotic therapy for stroke prevention in non-valvular atrial fibrillation

The world faces an epidemic of atrial fibrillation and atrial fibrillation-related stroke. An individual's risk of atrial fibrillation-related stroke can be estimated with the CHADS(2) or CHA(2)DS(2)VASc scores, and reduced by two-thirds with effective anticoagulation. Vitamin K antagonists, such as warfarin, are underused and often poorly managed. The direct thrombin inhibitor dabigatran etexilate and factor Xa inhibitors rivaroxaban and apixaban are new oral anticoagulants that are at least as efficacious and safe as warfarin. Their advantages are predictable anticoagulant effects, low propensity for drug interactions, and lower rates of intracranial haemorrhage than with warfarin. A disadvantage is the continuing need to develop and validate rapidly effective antidotes for major bleeding and standardised tests that accurately measure plasma concentrations and anticoagulant effects, together with the disadvantage of possible higher rates of gastrointestinal haemorrhage and greater expense than with warfarin. The new oral anticoagulants should increase the number of patients with atrial fibrillation at risk of stroke who are optimally anticoagulated, and reduce the burden of atrial fibrillation-related stroke.

[Reversal for heparins and new anticoagulant treatments]

Even with unfractionated heparin or derivates, the reversal of pharmacologic anticoagulation is crucial in anticoagulated patients developing a life-threatening bleeding or scheduled for an emergency procedure. The antagonisation of unfractionated heparin is well codified: each milligram of protamine sulfate antagonizes 100 IU of heparin. Measurement of thrombin time reflects the anti-IIa effect of heparin and has to be monitored immediately and 1hour after the injection of protamine. The required dose of protamine sulfate depends on dosage and time of LMWH administration, although no clinical study supports these data. To date, there is no effective antidote for new anticoagulants (fondaparinux and other pentasaccharides, direct thrombin inhibitors, direct anti-Xa inhibitors). Some preliminary studies suggest the effectiveness of recombinant activated factor VII for pentasaccharides and activated or not Prothrombin Complex Concentrates and recombinant activated factor VII for oral anti-Xa and anti-IIa agents. Therefore, while the characteristics of these new anticoagulants could increase the comfort and improve the compliance, their development needs to ascertain the lack of increase in bleeding complications and the need for a safe and effective antidote.

Dabigatran effects on the international normalized ratio, activated partial thromboplastin time, thrombin time, and fibrinogen: a multicenter, in vitro study

BACKGROUND

Patients receiving the direct thrombin inhibitor dabigatran may have selected anticoagulation assays performed as part of routine care. The effect of dabigatran on the international normalized ratio (INR), activated partial thromboplastin time (aPTT), thrombin time (TT), and fibrinogen requires clarification.

OBJECTIVE

To describe the effect of dabigatran on selected assays in North America and the United Kingdom.

METHODS

Pooled normal plasma enriched with dabigatran at concentrations of 25, 50, 75, 100, 125, 150, 200, 300, 400, and 500 ng/mL were sent blinded to 19 centers in the US, the UK, and Canada to assess the effect of dabigatran on routine coagulation screening tests, the INR, aPTT, TT, and fibrinogen.

RESULTS

Data were returned from 16 centers. For effects on INR, Neoplastine CI Plus and Simplastin HTF were the most sensitive and Thromborel S the least sensitive to increasing dabigatran concentrations. For the aPTT, all reagents demonstrated decreasing sensitivity to increasing dabigatran concentrations. Measured fibrinogen either demonstrated no change or factitious decrease with increasing dabigatran concentrations. Commercial TT methods were very sensitive to low concentrations of dabigatran, with 9 of 10 reporting sites exceeding test limits at dabigatran concentrations of 100 ng/mL.

CONCLUSIONS

The INR, aPTT, and TT rise as dabigatran concentrations increase. Both the INR and aPTT increase in a linear pattern with marginal slopes, creating challenges in using these assays as reliable means for assessing the amount of dabigatran present. The commercial TT assay is very sensitive at low concentrations of dabigatran. Fibrinogen test results may be either unaffected or lower in the presence of dabigatran.

Acute management of bleeding in patients on novel oral anticoagulants

Novel oral anticoagulants that directly inhibit thrombin (dabigatran) or factor Xa (rivaroxaban, apixaban) are currently available for prevention of venous thromboembolism (VTE) after orthopaedic surgery, treatment of acute VTE, and prevention of arterial thromboembolism in non-valvular atrial fibrillation. These agents offer advantages over VKAs, including rapid onset, shorter half-lives, fewer drug interactions, and lack of need for routine monitoring. However, there are no established agents to reverse their anticoagulant effect. We review the risk of bleeding with the novel oral anticoagulants and the limitations of conventional coagulation assays for measuring anticoagulant effect. We provide an approach to the management of patients with bleeding complications with evidence for various interventions for reversal, where available.

Large inter-individual variation of the pharmacodynamic effect of anticoagulant drugs on thrombin generation

Anticoagulation by a standard dosage of an inhibitor of thrombin generation presupposes predictable pharmacokinetics and pharmacodynamics of the anticoagulant. We determined the inter-individual variation of the effect on thrombin generation of a fixed concentration of direct and antithrombin-mediated inhibitors of thrombin and factor Xa. Thrombin generation was determined by calibrated automated thrombinography in platelet-poor plasma from 44 apparently healthy subjects which was spiked with fixed concentrations of otamixaban, melagatran, unfractionated heparin, dermatan sulfate and pentasaccharide. The variability of the inhibitory effect of the different anticoagulants within the population was determined using the coefficient of variation, i.e. the standard deviation expressed as a percentage of the mean. The inter-individual coefficients of variation of the endogenous thrombin potential and peak height before inhibition were 18% and 16%, respectively and became 20%-24% and 24%-43% after inhibition. The average inhibition of endogenous thrombin potential and peak height (ETP, peak) brought about by the anticoagulants was respectively: otamixaban (27%, 83%), melagatran (56%, 63%), unfractionated heparin (43%, 58%), dermatan sulfate (68%, 57%) and pentasaccharide (25%, 67%). This study demonstrates that the addition of a fixed concentration of any type of anticoagulant tested causes an inhibition that is highly variable from one individual to another. In this respect there is no difference between direct inhibitors of thrombin and factor Xa and heparin(-like) inhibitors acting on the same factors.

Assessment of the impact of rivaroxaban on coagulation assays: laboratory recommendations for the monitoring of rivaroxaban and review of the literature

INTRODUCTION

Rivaroxaban does not require monitoring nor frequent dose adjustment. However, searching for the optimal dose in the individual patient may be useful in some situations.

AIM

To determine which coagulation assay could be used to assess the impact of rivaroxaban on haemostasis and provide guidelines for the interpretation of routine lab tests.

MATERIALS

Rivaroxaban was spiked at concentrations ranging from 11 to 1,090 ng/mL in plateletpoor plasma. A large panel of coagulation assays was tested.

RESULTS

A concentration dependent prolongation of aPTT, PT, dPT, PiCT was observed. PT and dPT were the most sensitive chronometric assays but results varied depending on the reagent (Triniclot PT Excel S>Recombiplastin 2G>Neoplastin R>Neoplastin CI+>Triniclot PT Excel>Triniclot PT HTF>Innovin). FXa chromogenic assays showed the highest sensitivity. In TGA, Cmax was the most sensitive parameter with the tissue factor induced pathway. Rivaroxaban interferes on haemostasis diagnostic tests such the measurement of clotting factors, fibrinogen, antithrombin, proteins C and S, activated protein-C resistance and Xa-based chomogenic assays.

CONCLUSIONS

PT may be used as screening test to assess the risk of bleedings. A more specific and sensitive assay such as Biophen DiXaI using calibrators should be used to confirm the concentration of rivaroxaban. We also propose cut-off associated with a bleeding or thrombosis risk based on pharmacokinetic studies. Standardization of the time between the last intake of rivaroxaban and the sampling is mandatory.

Reversal of dabigatran anticoagulation by prothrombin complex concentrate (Beriplex P/N) in a rabbit model

BACKGROUND

One limitation of the direct thrombin inhibitor dabigatran is the lack of specific antidotes that allow acute bleeding events to be managed or urgent interventional procedures performed. Prothrombin complex concentrates (PCCs) have served as a standard treatment for the reversal of coumarin anticoagulation.

OBJECTIVES

This study was designed to determine in an animal model whether a PCC (Beriplex P/N) can effectively reverse the effects of dabigatran. An additional objective was to evaluate markers of dabigatran-associated bleeding diathesis.

METHODS

Anesthetized rabbits were treated with 0.4 mg kg(-1) dabigatran followed by PCC doses of 20, 35 or 50 IU kg(-1) or placebo. After a standardized kidney incision, volume of blood loss and time to hemostasis were determined.

RESULTS

From an initial mean of 29 mL, blood loss progressively declined by 5.44 mL with a 95% confidence interval (CI) of 2.21-8.67 mL per 10 IU kg(-1) increment in PCC dose (P = 0.002). At a PCC dose of 50 IU kg(-1) blood loss was fully normalized. Increasing PCC doses shortened the median time to hemostasis from 20.0 to 5.7 min (P < 0.001). The rate of hemostasis was nearly trebled with each 10 IU kg(-1) increment in PCC dose (rate ratio, 2.89; CI, 1.64-5.09).

CONCLUSIONS

In this animal study, PCC showed potential as an agent for reversing the effects of dabigatran. Further investigation is warranted.

New direct oral anticoagulants--current therapeutic options and treatment recommendations for bleeding complications

To date, clinical studies show that the incidence of spontaneous bleeding with new direct oral anticoagulants (DOAs) is comparable to that of established anticoagulants. However, unlike vitamin K antagonists, there are currently no clinically available antidotes or approved reversal agents for new DOAs. Restoring normal coagulation is important in many cases, such as emergency surgeries, serious bleedings, or anticoagulant overdosing. Attempts have been made to restore normal coagulation after treatment with new DOAs using compounds such as recombinant activated factor VII (rFVIIa), prothrombin complex concentrate (PCC), or FEIBA (factor eight inhibitor bypassing activity). Limited pre-clinical data and even less clinical evidence are available on the usefulness of these methods in restoring normal coagulation for the emergency management of critical bleeding episodes. Evaluating the utility of DOAs is further complicated by the fact that it is unknown how predictive established test systems are of the bleeding risks. Clinical practice requires further evaluation of the emergency management options for the new DOAs to define the agents and the doses that are most useful. Furthermore, patients receiving long-term treatment with a DOA are likely to undergo elective surgery at some point, and there is lack of evidence regarding perioperative treatment regimens under such conditions. This review summarises potential bleeding management options and available data on the new DOAs.

Dabigatran: review of pharmacology and management of bleeding complications of this novel oral anticoagulant

Dabigatran (Pradaxa) is a competitive direct thrombin inhibitor approved by the US FDA for prevention of embolic stroke in patients with nonvalvular atrial fibrillation. Dabigatran has a pharmacokinetic profile that produces predictable anticoagulation responses, does not undergo CYP 450 metabolism, has few drug-drug and drug-food interactions, and does not require frequent laboratory monitoring of clotting parameters. Clinicians are rapidly prescribing this agent as a replacement for warfarin therapy. However, no therapeutic agent has been accepted to reliably reverse the hemorrhagic complications of dabigatran. As of yet, there is no solid evidence to guide management of bleeding complications; management should start with local control of bleeding when possible and transfusion of pRBCs if needed. Transfusion of FFP would not be expected to help control bleeding. Limited and mixed data exist for transfusion of factor VIIa and prothrombin complex concentrates; these therapies should be considered as well as dialysis, which will increase elimination in patients with life-threatening or closed-space bleeding due to dabigatran. We present an article that reviews the pharmacokinetics, clinical trial literature, and consensus guidelines regarding this novel oral anticoagulant.

Rivaroxaban in Nonvalvular Atrial Fibrillation

Each month, subscribers to The Formulary Monograph Service receive 5 to 6 well-documented monographs on drugs that are newly released or are in late phase 3 trials. The monographs are targeted to Pharmacy & Therapeutics Committees. Subscribers also receive monthly 1-page summary monographs on agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation/medication use evaluation (DUE/MUE) is also provided each month. With a subscription, the monographs are sent in print and are also available on-line. Monographs can be customized to meet the needs of a facility. Subscribers to The Formulary Monograph Service also receive access to a pharmacy bulletin board, The Formulary Information Exchange (The F.I.X.). All topics pertinent to clinical and hospital pharmacy are discussed on The F.I.X. A drug class review is now published monthly with The Formulary Monograph Service. Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. For more information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The April 2012 monograph topics are on ivacaftor, vismodegib, axitinib, glucarpidase, and loxapine inhalation. The DUE/MUE is on glucarpidase.

Impact of dabigatran on a large panel of routine or specific coagulation assays. Laboratory recommendations for monitoring of dabigatran etexilate

Due to low bioavailability and high inter-individual variability, monitoring of dabigatran may be required in specific situations to prevent the risk of bleedings or thrombosis. The aim of the study was to determine which coagulation assay(s) could be used to assess the impact of dabigatran on secondary haemostasis. Dabigatran was spiked at concentrations ranging from 4.7 ng/ml to 943.0 ng/ml in pooled citrated human platelet-poor plasma. The following clotting assays were performed: prothrombin time (PT); activated partial thromboplastin time (aPTT); thrombin time (TT); ecarin clotting time (ECT); ecarin chromogenic assay (ECA); prothrombinase-induced clotting time (PiCT); activated clotting time (ACT); Hemoclot Thrombin Inhibitor (HTI) and thrombin generation assay (TGA). A concentration-dependent prolongation of PT, dPT, and aPTT was observed with aPTT being the more sensitive test. The results varied mostly due to the clotting reagent. HTI, ECT and TGA were the most sensitive tests but are not available 24 hours a day. In addition, HTI showed a linear correlation with a good reproducibility. Dabigatran induced a concentration-dependent delay and inhibition of tissue factor-induced TGA. Cut-offs related with higher risk of bleedings or thrombosis were defined for each reagent of aPTT and HTI. In conclusion, aPTT could be used for the monitoring of dabigatran and as screening test for the risk of overdose. However, because of its higher sensitivity, good reproducibility, excellent linear correlation at all doses, its simplicity of use, and possibilities of automation, HTI should be considered as the gold-standard.

Evaluation of the anti-factor Xa chromogenic assay for the measurement of rivaroxaban plasma concentrations using calibrators and controls

Rivaroxaban is an oral, direct factor Xa inhibitor. Routine coagulation monitoring is not required, but a quantitative determination of rivaroxaban concentrations might be useful in some clinical circumstances. This multicentre study assessed the suitability of the anti-factor Xa chromogenic assay for the measurement of rivaroxaban plasma concentrations (ng/ml) using rivaroxaban calibrators and controls, and the inter-laboratory precision of the measurement. Twenty-four centres in Europe and North America were provided with sets of rivaroxaban calibrators (0, 41, 209 and 422 ng/ml) and a set of rivaroxaban pooled human plasma controls (20, 199 and 662 ng/ml; the concentrations were unknown to the participating laboratories). The evaluation was carried out over 10 days by each laboratory using local anti-factor Xa reagents as well as the centrally provided reagent, a modified STA® Rotachrom® assay. A calibration curve was produced each day, and the day-to-day precision was evaluated by testing three human plasma controls. When using the local anti-factor Xa reagents, the mean rivaroxaban concentrations (measured/actual values) were: 17/20, 205/199 and 668/662 ng/ml, and the coefficient of variance (CV) was 37.0%, 13.7% and 14.1%, respectively. When the modified STA Rotachrom method was used, the measured/actual values were: 18/20, 199/199 and 656/662 ng/ml, and the CV was 19.1%, 10.9% and 10.0%, respectively. The results suggest that, by using rivaroxaban calibrators and controls, the anti-factor Xa chromogenic method is suitable for measuring a wide range of rivaroxaban plasma concentrations (20-660 ng/ml), which covers the expected rivaroxaban plasma levels after therapeutic doses.

Rivaroxaban

Each month, subscribers to The Formulary Monograph Service receive 5 to 6 well-documented monographs on drugs that are newly released or are in late phase 3 trials. The monographs are targeted to Pharmacy & Therapeutics Committees. Subscribers also receive monthly 1-page summary monographs on agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation/medication use evaluation (DUE/MUE) is also provided each month. With a subscription, the monographs are sent in print and are also available on-line. Monographs can be customized to meet the needs of a facility. Subscribers to The Formulary Monograph Service also receive access to a pharmacy bulletin board, The Formulary Information Exchange (The F.I.X.). All topics pertinent to clinical and hospital pharmacy are discussed on The F.I.X. Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. For more information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The December 2011 monograph topics are on deferiprone tablets, tapentadol extended-release tablets, crizotinib, tadalafil tablets for BPH, and vismodegib. The DUE/MUE is on deferiprone tablets.

Rivaroxaban: Quantification by anti-FXa assay and influence on coagulation tests: a study in 9 Swiss laboratories

INTRODUCTION

Rivaroxaban (RXA) is licensed for prophylaxis of venous thromboembolism after major orthopaedic surgery of the lower limbs. Currently, no test to quantify RXA in plasma has been validated in an inter-laboratory setting. Our study had three aims: to assess i) the feasibility of RXA quantification with a commercial anti-FXa assay, ii) its accuracy and precision in an inter-laboratory setting, and iii) the influence of 10mg of RXA on routine coagulation tests.

METHODS

The same chromogenic anti-FXa assay (Hyphen BioMed) was used in all participating laboratories. RXA calibrators and sets of blinded probes (aim ii.) were prepared in vitro by spiking normal plasma. The precise RXA content was assessed by high-pressure liquid chromatography-tandem mass spectrometry. For ex-vivo studies (aim iii), plasma samples from 20 healthy volunteers taken before and 2 - 3hours after ingestion of 10mg of RXA were analyzed by participating laboratories.

RESULTS

RXA can be assayed chromogenically. Among the participating laboratories, the mean accuracy and the mean coefficient of variation for precision of RXA quantification were 7.0% and 8.8%, respectively. Mean RXA concentration was 114±43μg/L .RXA significantly altered prothrombin time, activated partial thromboplastin time, factor analysis for intrinsic and extrinsic factors. Determinations of thrombin time, fibrinogen, FXIII and D-Dimer levels were not affected.

CONCLUSIONS

RXA plasma levels can be quantified accurately and precisely by a chromogenic anti-FXa assay on different coagulometers in different laboratories. Ingestion of 10mg RXA results in significant alterations of both PT- and aPTT-based coagulation assays.