Dabigatran etexilate: a new oral thrombin inhibitor

Measurement of dabigatran in standardly used clinical assays, whole blood viscoelastic coagulation, and thrombin generation assays

Dabigatran, a direct thrombin inhibitor, is increasingly used clinically as one of the new oral anticoagulants. This review summarizes the assays available to measure its activity and includes the relative sensitivity of the different assays for this agent. In addition to plasma-based clotting tests, assays commonly used in surgical/emergency settings, such as activated clotting time and thromboelastometry/thromboelastography, are reviewed. In addition, the thrombin generation assay is discussed as an important method to determine the potential risk of thrombosis or bleeding and its relevance to the measurement of direct thrombin inhibitors.

Dabigatran in secondary stroke prevention: clinical experience with 106 patients

INTRODUCTION

Our aim was to analyze our clinical experience with dabigatran etexilate in secondary stroke prevention.

METHODS

We retrospectively included patients starting dabigatran etexilate for secondary stroke prevention from March 2010 to December 2012. Efficacy and safety variables were registered.

RESULTS

106 patients were included, median follow-up of 12 months (range 1-31). Fifty-six females (52.8%), mean age 76.4 (range 50-95, SD 9.8), median CHADS2 4 (range 2-6), CHA2DS2-VASc 5 (range 2-9), and HAS-BLED 2 (range 1-5). Indication for dabigatran etexilate was ischemic stroke in 101 patients and acute cerebral hemorrhage (CH) due to warfarin in 5 (4.7%). Dabigatran etexilate 110 mg bid was prescribed in 71 cases (67%) and 150 mg bid was prescribed in the remaining. Seventeen patients (16%) suffered 20 complications during follow-up. Ischemic complications (10) were 6 transient ischemic attacks (TIA), 3 ischemic strokes, and 1 acute coronary syndrome. Hemorrhagic complications (10) were CH (1), gastrointestinal bleeding (6), mild hematuria (2), and mild metrorrhagia (1), leading to dabigatran etexilate discontinuation in 3 patients. Patients with previous CH remained uneventful. Three patients died (pneumonia, congestive heart failure, and acute cholecystitis) and 9 were lost during follow-up.

CONCLUSIONS

Dabigatran etexilate was safe and effective in secondary stroke prevention in clinical practice, including a small number of patients with previous history of CH.

Transfer of dabigatran and dabigatran etexilate mesylate across the dually perfused human placenta

OBJECTIVE

To assess the transplacental pharmacokinetics at term of the oral thrombin inhibitor, dabigatran, and its prodrug, dabigatran etexilate mesylate, to estimate fetal drug exposure.

METHODS

Placentae were obtained with informed consent after cesarean delivery of healthy term pregnancies in Toronto, Ontario, Canada. The transplacental transfer of dabigatran and dabigatran etexilate mesylate was separately assessed using the ex vivo dual perfusion of an isolated human placental cotyledon. Dabigatran, at a concentration of 35 ng/mL, was added to the maternal circulation at the start of the experimental phase. Maternal and fetal samples were taken throughout the preexperimental (1 hour) and experimental (3 hours) phases for measurement of dabigatran and markers of placental viability. Separate placenta perfusions with dabigatran etexilate mesylate were conducted at an initial maternal concentration of 3.5 ng/mL. Dabigatran and dabigatran etexilate mesylate were measured using liquid chromatography-tandem mass spectrometry.

RESULTS

There was slower transfer of dabigatran compared with antipyrine from the maternal-to-fetal circulation, because the median fetal-to-maternal concentration ratio was 0.33 (interquartile range 0.29-0.38) after 3 hours (n=3). The prodrug, dabigatran etexilate mesylate, had limited placental transfer as characterized by a fetal-to-maternal ratio of 0.17 (interquartile range 0.15-0.17) after 3 hours (n=3). Placental viability markers for all perfusions were within normal ranges.

CONCLUSION

This report provides direct evidence of the transfer of dabigatran and its prodrug across the term human placenta from the mother to the fetus. From a clinical perspective, these data suggest that, pending further study, dabigatran should not be used for anticoagulation of pregnant women, because the drug may have an adverse effect on fetal blood coagulation.

How do we manage cardiopulmonary bypass coagulopathy?

BACKGROUND

Patients who undergo cardiopulmonary bypass (CPB) are at risk for coagulopathy. Suboptimal turnaround time (TAT) of laboratory coagulation testing results in empiric administration of blood products to treat massive bleeding. We describe our initiative in establishing the coagulation-based hemotherapy (CBH) service, a clinical pathology consultation service that uses rapid TAT coagulation testing and provides comprehensive assessment of bleeding in patients undergoing CPB. A transfusion algorithm that treats the underlying cause of coagulopathy was developed.

STUDY DESIGN AND METHODS

The coagulation testing menu includes all aspects of coagulopathy with close proximity of the laboratory to the operating room to allow for rapid test results. The hemotherapy pathologist monitors laboratory results at several stages in surgery and uses a comprehensive algorithm to monitor a patient's hemostasis. The optimal number and type of blood products are selected when the patient is taken off CPB.

RESULTS

The CBH service was consulted for 44 ventricular assist device implants, 30 heart transplants, and 31 other cardiovascular surgeries from May 2012 through November 2013. The TAT for laboratory tests was 15 minutes for complete blood count, antithrombin, and coagulation panel and 30 minutes for VerifyNow and thromboelastography, in comparison to 45 to 60 minutes in normal settings. The transfusion algorithms were used with optimal administration of blood components with preliminary data suggestive of reduced blood product usage and better patient outcomes.

CONCLUSION

We described the successful introduction of a novel pathology consultation service that uses a rapid TAT coagulation testing menu with transfusion algorithms for improved management of CPB patients.

The role of novel anticoagulants in the management of venous thromboembolism

Venous thromboembolism (VTE) is a common health condition with a high mortality and morbidity as well as significant health cost. Traditional treatment with parenteral heparin followed by vitamin K antagonist (VKA) has helped to decrease both morbidity and mortality over years. However, difficulties with warfarin such as INR monitoring, drug-drug interactions, and dietary restrictions has led to research for new anticoagulants. Thus, novel anticoagulants such as direct thrombin and factor X inhibitors have been developed and studied for various indications including the management of VTE. There is now good evidence that some novel anticoagulants are at least as effective as traditional anticoagulation therapy with probably safer outcomes. We have reviewed the literature on the medical management of VTE with the focus on the role of dabigatran, rivaroxaban, apixaban and edoxaban for this indication.

Comparison of minor bleeding complications using dabigatran or enoxaparin after cemented total hip arthroplasty

BACKGROUND

Orally administered chemical thromboprophylactic agents for total hip replacement (THR) have become popular in recent years. Certain clinical trials suggest that the efficacy and the risk of major bleeding after administration of direct thrombin inhibitor dabigatran etexilate are equivalent to the clinical trial comparator, subcutaneous low-molecular-weight heparin enoxaparin. Our aim was to compare and evaluate the incidence of minor haemorrhagic and soft-tissue adverse effects of enoxaparin and dabigatran.

MATERIALS AND METHODS

122 patients who were treated by elective cemented primary THR were enrolled in our quasi-randomised study. Two groups were formed according to which perioperative thromboprophylactic agent was used: 61 patients in enoxaparin group versus 61 patients in dabigatran group. Thigh volume changes, calculated perioperative blood loss, area of haematoma, wound bleeding, duration of wound discharge and intensity of serous wound discharge on postoperative day 3 and day 7 were recorded.

RESULTS

The duration and intensity of serous wound discharge differed significantly between the two groups. Duration of wound discharge after drain removal was 2.2 (±2.7) days in the dabigatran group and 1.2 (±1.9) days in the enoxaparin group (p < 0.05). Significant increase in serous discharge was found in the dabigatran group (p < 0.05) on third and seventh postoperative days compared to the enoxaparin group.

CONCLUSION

Both thromboprophylactic agents were found to have appropriate antithrombotic effects after THR. However, dabigatran was associated with an increased incidence of prolonged serous wound discharge, which might cause longer hospitalization and might instigate the use of prolonged antibiotic prophylaxis.

Comparison of the phase III clinical trial designs of novel oral anticoagulants versus warfarin for the treatment of nonvalvular atrial fibrillation: implications for clinical practice

Although vitamin K antagonists (VKAs) have been the backbone of thromboprophylaxis in nonvalvular atrial fibrillation, their limitations have encouraged the development of a new generation of oral anticoagulants. This review compares the different designs and procedures used to conduct four phase III trials that tested dabigatran, rivaroxaban, apixaban, and edoxaban versus VKAs. Although pharmacologic characteristics and results of the main trials are briefly discussed, this review mainly focuses on study designs, enrollment criteria, populations studied, quality metrics, and transition strategies between oral anticoagulants. While each of the trials was of high quality, performed independently, and led by independent academic groups, substantial differences exist in terms of drug pharmacology and trial characteristics. Caution is advised when comparing results across trials as practicing clinicians strive to personalize anticoagulation treatments for their individual patients. We believe that the differences in the pharmacokinetic and pharmacodynamic profiles of the available novel oral anticoagulants (NOACs), coupled with substantial heterogeneity in the trial populations and designs and procedures used to conduct the trials, support an important role for each of the NOACs dependent upon the specific clinical scenario faced by the practicing clinician.

A Review of and Recommendations for the Management of Patients With Life-Threatening Dabigatran-Associated Hemorrhage

Dabigatran is an oral direct thrombin inhibitor that is approved for the prevention of stroke and systemic embolism in nonvalvular atrial fibrillation. Dabigatran has several advantages over warfarin including predictable pharmacokinetics and pharmacodynamics which eliminates the need for routine laboratory monitoring, superiority over warfarin in preventing stroke, or systemic embolism without having an increased risk of bleeding. However, as with any anticoagulant, there remains a real chance of bleeding, including major or life-threatening hemorrhage. Many physicians feel comfortable managing bleeding complications on older anticoagulants like warfarin and heparin, due to extensive experience with the medications along with antidotes to reverse their effects as well as established protocols for treating anticoagulant-associated hemorrhage. However, most physicians have limited clinical experience with dabigatran, there is no specific antidote for dabigatran reversal and there is a paucity of protocols, guidelines, and recommendations for how to manage dabigatran-associated hemorrhage. In this review, we present a case series of patients admitted to our institution for management of bleeding while receiving dabigatran. We retrospectively reviewed these cases to evaluate the efficacy and rationale of the various anticoagulation reversal strategies employed in the context of the existing evidence found in the literature. Specific focus is placed on the therapies utilized and the coagulation studies used to manage these patients.

How I treat target-specific oral anticoagulant–associated bleeding

Target-specific oral anticoagulants (TSOACs) that directly inhibit thrombin (dabigatran) or factor Xa (rivaroxaban, apixaban) are effective and safe alternatives to vitamin K antagonists (VKAs) and low-molecular-weight heparin (LMWH). Although these agents have practical advantages compared with VKAs and LMWH, there are no antidotes that reverse their anticoagulant effect. Clinical evidence for the efficacy of nonspecific therapies that promote formation of fibrin (prothrombin complex concentrate [PCC], activated PCC [aPCC], and recombinant factor VIIa) in the setting of TSOAC-associated bleeding is lacking, and these prohemostatic products are associated with a risk of thrombosis. In the absence of specific antidotes, addition of PCC or aPCC to maximum supportive therapy may be reasonable for patients with severe or life-threatening TSOAC-associated bleeding. Targeted antidotes for these agents are in development.

Novel oral anticoagulants for stroke prevention in the geriatric population

Prior to the availability of several newer anticoagulant medications, there had been no new advances in anticoagulation management for stroke prevention since the advent of warfarin in the 1950s. The availability of the novel oral anticoagulants (NOACs) dabigatran, rivaroxaban,and apixaban represent improvements over warfarin in many respects, including the elimination of the need for therapeutic drug monitoring, fewer drug and food interactions,and favorable efficacy; however, these agents are not without risk. Specifically, the use of the NOACs in the geriatric population, who are more likely to have an increased risk of stroke due to atrial fibrillation and other medical comorbidities, is not without risk. The objective of this review is to update the clinician on the use of the NOACs in the geriatric population and introduce the controversies and risks surrounding these newer therapies.

New anticoagulant and antiplatelet agents: a primer for the gastroenterologist

A large number of patients worldwide receive anticoagulant and antiplatelet agents, collectively known as antithrombotic agents. Several new anticoagulants and antiplatelet agents recently were approved for use. Gastroenterologists may be unfamiliar with the mechanism of action, indications for use, and pharmacokinetics of these newer drugs. In patients undergoing elective and urgent endoscopic procedures, clinicians must be familiar with these medications to optimize outcomes. When the decision is made to continue the newer antithrombotic agents for elective procedures, the clinician must understand the risk that these agents may impart on procedural-induced bleeding. Finally, it is important to understand how to manage these agents in the presence of acute gastrointestinal bleeding. In this article the use of newer antithrombotic agents is reviewed.

New anticoagulants and antiplatelet agents: a primer for the clinical gastroenterologist

The discovery of the first oral anticoagulant, warfarin, was a milestone in anticoagulation. Warfarin's well-known limitations, however, have led to the recent development of more effective anticoagulants. The rapidly growing list of these drugs, however, presents a challenge to endoscopists who must treat patients on these sundry medications. This review is intended to summarize the pharmacological highlights of new anticoagulants, with particular attention to suggested "best-practice" recommendations for the withholding of these drugs before endoscopic procedures.

5-Chlorothiophene-2-carboxylic acid [(S)-2-[2-methyl-3-(2-oxopyrrolidin-1-yl)benzenesulfonylamino]-3-(4-methylpiperazin-1-yl)-3-oxopropyl]amide (SAR107375), a selective and potent orally active dual thrombin and factor Xa inhibitor

Compound 15 (SAR107375), a novel potent dual thrombin and factor Xa inhibitor resulted from a rational optimization process. Starting from compound 14, with low factor Xa and modest anti-thrombin inhibitory activities (IC50's of 3.5 and 0.39 μM, respectively), both activities were considerably improved, notably through the incorporation of a neutral chlorothiophene P1 fragment and tuning of P2 and P3-P4 fragments. Final optimization of metabolic stability with microsomes led to the identification of 15, which displays strong activity in vitro vs factor Xa and thrombin (with Ki's of 1 and 8 nM, respectively). In addition 15 presents good selectivity versus related serine proteases (roughly 300-fold), including trypsin (1000-fold), and is very active (0.39 μM) in the thrombin generation time (TGT) coagulation assay in human platelet rich plasma (PRP). Potent in vivo activity in a rat model of venous thrombosis following iv and, more importantly, po administration was also observed (ED50 of 0.07 and 2.8 mg/kg, respectively). Bleeding liability was reduced in the rat wire coil model, more relevant to arterial thrombosis, with 15 (blood loss increase of 2-fold relative to the ED80 value) compared to rivaroxaban 2 and dabigatran etexilate 1a.

Evaluation of dabigatran utilization and risk among hospitalized patients

BACKGROUND

Few data exist to evaluate the use of dabigatran among hospitalized patients and this population that may be at increased risk for toxicity or reduced efficacy. As such, the objectives of this study were to describe the characteristics of hospitalized patients prescribed dabigatran and to compare select characteristics with patients included in the Randomized Evaluation of Long-Term Anticoagulation (RE-LY) phase III clinical trial.

METHODS

A cross-sectional study was performed at Upstate University Hospital. Select patient characteristics, including age, renal function, and drug interaction exposure, were compared with those for patients in the RE-LY trial.

RESULTS

The study included 140 patients. Mean age was 69.7 years (SD = 13.8) and 72 (51.4%) were male. The mean CHADS2 score was 2.48 as compared with 2.2 in RE-LY. Significantly more patients in our study had moderate to severe renal dysfunction (creatinine clearance [CrCl] < 50 mL/min) as compared with the RE-LY trial (27.5% vs 19.4%, P = .0207) when analyzing our study patients' worst recorded CrCl. Among the 29 patients prescribed dose-adjusted dabigatran, 3 were correctly dose adjusted, 2 were overdosed, and 26 were underdosed. At least 1 pharmacokinetic drug interaction with dabigatran occurred in 110 study patients (78.6%). Use of proton pump inhibitors was more predominant in our study population when compared with RE-LY (64.3% vs 13.9%, P < .0001).

CONCLUSIONS

Hospitalized patients exhibit multiple characteristics that place them at heightened risk for altered dabigatran drug concentrations and may have a heightened risk for clinical sequelae related to dabigatran use.

Dabigatran etexilate for thromboembolic prophylaxis in non-valvular atrial fibrillation: the RE-LY study and substudies with commentary

In 2010, dabigatran etexilate, a direct thrombin inhibitor, was the first new oral anticoagulant to be approved for thromboembolic prophylaxis in atrial fibrillation in over 50 years. Dabigatran, unlike warfarin, has a short half-life with a rapid onset of anticoagulant effect, does not require dose adjustment or monitoring, and does not interact with food. The RE-LY trial compared two doses of dabigatran (110 and 150 mg twice daily) with adjusted dose warfarin in patients with non-valvular atrial fibrillation and at least 1 stroke risk factor. Compared with warfarin, dabigatran 150 mg twice daily was superior in reducing the risk of stroke or systemic embolism and was associated with a similar rate of major bleeding, while dabigatran 110 mg twice daily was equally effective in reducing stroke or systemic embolism and was associated with less major bleeding. Despite these favorable results, there remains disagreement regarding the optimal dose and overall safety of dabigatran in certain patient populations including the elderly and those with renal dysfunction.

New aspects on efficient anticoagulation and antiplatelet strategies in sheep

BACKGROUND

After addressing fundamental questions in preclinical models in vitro or in small animals in vivo, the translation into large animal models has become a prerequisite before transferring new findings to human medicine. Especially in cardiovascular, orthopaedic and reconstructive surgery, the sheep is an important in vivo model for testing innovative therapies or medical devices prior to clinical application. For a wide variety of sheep model based research projects, an optimal anticoagulation and antiplatelet therapy is mandatory. However, no standardised scheme for this model has been developed so far. Thus the efficacy of antiplatelet (acetylsalicylic acid, clopidogrel, ticagrelor) and anticoagulant (sodium enoxaparin, dabigatran etexilate) strategies was evaluated through aggregometry, anti-factor Xa activity and plasma thrombin inhibitor levels in sheep of different ages.

RESULTS

Responses to antiplatelet and anticoagulant drugs in different concentrations were studied in the sheep. First, a baseline for the measurement of platelet aggregation was assessed in 20 sheep. The effectiveness of 225 mg clopidogrel twice daily (bid) in 2/5 sheep and 150 mg bid in 3/5 lambs could be demonstrated, while clopidogrel and its metabolite carboxylic acid were detected in every plasma sample. High dose ticagrelor (375 mg bid) resulted in sufficient inhibition of platelet aggregation in 1/5 sheep, while acetylsalicylic acid did not show any antiplatelet effect. Therapeutic anti-factor Xa levels were achieved with age-dependent dosages of sodium enoxaparin (sheep 3 mg/kg bid, lambs 5 mg/kg bid). Administration of dabigatran etexilate resulted in plasma concentrations similar to human ranges in 2/5 sheep, despite receiving quadruple dosages (600 mg bid).

CONCLUSION

High dosages of clopidogrel inhibited platelet aggregation merely in a low number of sheep despite sufficient absorption. Ticagrelor and acetylsalicylic acid cannot be recommended for platelet inhibition in sheep. Efficient anticoagulation can be ensured using sodium enoxaparin rather than dabigatran etexilate in age-dependent dosages. The findings of this study significantly contribute to the improvement of a safe and reliable prophylaxis for thromboembolic events in sheep. Applying these results in future translational experimental studies may help to avoid early dropouts due to thromboembolic events and associated unnecessary high animal numbers.

Practical Issues to Prevent Stroke Associated with Non-valvular Atrial Fibrillation

Stroke associated with non-valvular atrial fibrillation (NVAF) is one of the most important subtypes of ischemic stroke, and its importance is becoming even more apparent in an aging population. To assess the risk of stroke associated with NVAF, the CHADS2 and CHA2DS2-VASc scores are mainly used. Such scores can be used to predict the recurrence and prognosis of ischemic stroke. In addition, new oral anticoagulants (NOACs) and devices are being evaluated in the prevention of stroke associated with NVAF in addition to treatment with the conventional oral anticoagulant, warfarin. Since clinical experience with NOACs is not globally sufficient, a cautious approach is needed.

Current and new oral antithrombotics in non-valvular atrial fibrillation: a network meta-analysis of 79 808 patients

BACKGROUND

Antithrombotic therapy reduces stroke, embolism and mortality in patients with atrial fibrillation (AF); however, meta-analyses have focused on pairwise comparisons of treatments.

OBJECTIVE

To synthesise the evidence from trials using a multiple treatment comparison methods thereby permitting a broader comparison across multiple therapies.

DESIGN, SETTING, PATIENTS

Randomised controlled trials in patients with AF of antithrombotics were identified from MEDLINE, Embase, and Cochrane Central Register of Controlled Trials through May 2012. We performed a random-effects model within a Bayesian framework using Markov Chain Monte Carlo simulation to calculate pooled OR and 95% credibility intervals (CrI). We also ranked therapies by their likelihood of leading to the best results for the outcomes.

MAIN OUTCOME MEASURE

Multiple endpoints including stroke, embolism, death and bleeding.

RESULTS

We identified 20 studies with 79 808 patients allocated to 8 treatments: ASA, ASA plus clopidogrel, vitamin K antagonists (VKAs), dabigatran 110 mg, dabigatran 150 mg, rivaroxaban, apixaban or placebo/control. Compared with placebo/control, dabigatran 150 mg was associated with the lowest risk of stroke (OR=0.25, 0.15-0.43), the composite of ischaemic stroke or systemic embolism (OR=0.26, 0.12-0.54) and mortality (OR=0.53, 0.28-0.88). ASA plus clopidogrel was associated with the highest risk of major bleeding (OR=3.65, 1.22-13.56). In simulated comparisons, the novel oral anticoagulants ranked better than VKA or antiplatelet therapies for prevention of stroke, ischaemic stroke or systemic embolism and mortality.

CONCLUSIONS

In this network meta-analysis, novel oral anticoagulants were the most promising treatments to reduce stroke, stroke or systemic embolism, and all-cause mortality in patients with AF.

Anticoagulant therapy with the oral direct factor Xa inhibitors rivaroxaban, apixaban and edoxaban and the thrombin inhibitor dabigatran etexilate in patients with hepatic impairment

The direct factor Xa (FXa) inhibitors rivaroxaban, apixaban and edoxaban, and the thrombin inhibitor dabigatran etexilate (dabigatran) have gained approval for use in several indications, most notably for the prevention and treatment of venous thromboembolism (VTE) and for the prevention of stroke in patients with atrial fibrillation. Hepatic impairment can affect the disposition of these anticoagulants considerably not only because of the hepatic metabolism of the direct FXa inhibitors but also because moderate to severely impaired hepatic function will affect coagulation. This review describes the key pharmacological properties of novel oral anticoagulants with special attention to patients with impaired hepatic function. In subjects with moderately impaired liver function (i.e. Child-Pugh classification B), the area under the plasma concentration-time curve (AUC) of rivaroxaban (10 mg single dose) is increased by 2.27-fold, which is paralleled by an increase in FXa inhibition. The AUC of apixaban (5 mg single dose) is increased by 1.09-fold, whereas the AUC of edoxaban (15 mg single dose) is decreased by 4.8 % and the AUC of dabigatran (150 mg single dose) is decreased by 5.6 %. Specific labelling restrictions for rivaroxaban, apixaban and dabigatran regarding impaired hepatic function are based on both the Child-Pugh classification and liver-related exclusion criteria applied in pivotal clinical trials. Rivaroxaban is contraindicated in patients with hepatic disease associated with coagulopathy and clinically relevant bleeding risk, including cirrhotic patients classified as Child-Pugh B and C. Apixaban can be used with caution in patients with mild (Child-Pugh A) or moderate (Child-Pugh B) hepatic impairment or in patients with alanine aminotransferase and aspartate aminotransferase levels >2× upper limit of normal (ULN). Apixaban is not recommended in patients with severe hepatic impairment and is contraindicated in those with hepatic disease associated with coagulopathy and clinically relevant bleeding risk. Dabigatran is not recommended in patients with elevated liver enzymes (>2× ULN). Dabigatran is contraindicated in patients with hepatic impairment or liver disease expected to have any impact on survival. Currently, edoxaban is not available in the US or European markets. However, the Japanese label did not restrict use in hepatic dysfunction but advises care in patients with severe hepatic impairment.

A review of apixaban for stroke prevention in atrial fibrillation: insights from ARISTOTLE

Atrial fibrillation (AF) is associated with significant mortality and morbidity, and stroke represents the most-feared complication. Consequently, AF treatment has focused on thromboprophylaxis, with warfarin as the mainstay of therapy. However, concerns over ease of use and safety have limited its use. Three novel oral anticoagulants have been approved for use in stroke prevention in AF based on randomized data: 1) dabigatran, studied in Randomized Evaluation of Long-term Anticoagulation Therapy (RE-LY); 2) rivaroxaban, studied in Rivaroxaban Once-daily, Oral, Direct Factor Xa Inhibition Compared with Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation (ROCKET AF); and 3) apixaban, studied in Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation (ARISTOTLE). In this review, we focus on apixaban and discuss subgroup analyses that have been performed in the three trials comparing novel oral anticoagulants with warfarin. We conclude with recommendations regarding further investigations.

Disadvantages of VKA and requirements for novel anticoagulants

Vitamin K antagonists have been in wide use for over 70 years. Warfarin, the most commonly used vitamin K antagonist, has been shown to be highly effective in treating and preventing thrombosis. Despite this, warfarin has many disadvantages, which has led to the development of a new class of oral anticoagulants targeted to specific coagulation factors designated as target-specific oral anticoagulants (TSOAs). TSOAs include the thrombin inhibitors (dabigatran) and factor Xa inhibitors (rivaroxaban, apixaban). This chapter reviews the disadvantages of warfarin and evaluates both the advantages and disadvantages of the new oral anticoagulants.

Dabigatran and kidney disease: a bad combination

Dabigatran is an oral direct thrombin inhibitor widely used to prevent and treat various thromboembolic complications. An advantage of this agent over other anticoagulants is that routine laboratory monitoring and related dose adjustments are considered unnecessary. A major disadvantage is the absence of a reliable means of reversing its anticoagulant effect. After U.S. Food and Drug Administration approval, recently emerged data suggest a higher bleeding risk with dabigatran, especially in the elderly. Clinicians are thus faced with caring for patients with serious bleeding events without readily available tests to measure drug levels or the anticoagulant effects of dabigatran and without effective antidotes to rapidly reverse the anticoagulant effect. On the basis of dabigatran's pharmacokinetic profile, hemodialysis and continuous renal replacement therapy have been used to remove dabigatran with the hope, still unproven, that this would rapidly reverse the anticoagulant effect and reduce bleeding in patients with normal and those with reduced kidney function. However, the best clinical approach to the patient with serious bleeding is not known, and the risks of placing a hemodialysis catheter in an anticoagulated patient can be substantial. This article reviews this issue, addressing clinical indications, drug pharmacokinetics, clinical and laboratory monitoring tests, and dialytic and nondialytic approaches to reduce bleeding in dabigatran-treated patients.

New oral anticoagulants: comparative pharmacology with vitamin K antagonists

New oral anticoagulants (OACs) that directly inhibit Factor Xa (FXa) or thrombin have been developed for the long-term prevention of thromboembolic disorders. These novel agents provide numerous benefits over older vitamin K antagonists (VKAs) due to major pharmacological differences. VKAs are economical and very well characterized, but have important limitations that can outweigh these advantages, such as slow onset of action, narrow therapeutic window and unpredictable anticoagulant effect. VKA-associated dietary precautions, monitoring and dosing adjustments to maintain international normalized ratio (INR) within therapeutic range, and bridging therapy, are inconvenient for patients, expensive, and may result in inappropriate use of VKA therapy. This may lead to increased bleeding risk or reduced anticoagulation and increased risk of thrombotic events. The new OACs have rapid onset of action, low potential for food and drug interactions, and predictable anticoagulant effect that removes the need for routine monitoring. FXa inhibitors, e.g. rivaroxaban and apixaban, are potent, oral direct inhibitors of prothrombinase-bound, clot-associated or free FXa. Both agents have a rapid onset of action, a wide therapeutic window, little or no interaction with food and other drugs, minimal inter-patient variability, and display similar pharmacokinetics in different patient populations. Since both are substrates, co-administration of rivaroxaban and apixaban with strong cytochrome P450 (CYP) 3A4 and permeability glycoprotein (P-gp) inhibitors and inducers can result in substantial changes in plasma concentrations due to altered clearance rates; consequently, their concomitant use is contraindicated and caution is required when used concomitantly with strong CYP3A4 and P-gp inducers. Although parenteral oral direct thrombin inhibitors (DTIs), such as argatroban and bivalirudin, have been on the market for years, DTIs such as dabigatran are novel synthetic thrombin antagonists. Dabigatran etexilate is a low-molecular-weight non-active pro-drug that is administered orally and converted rapidly to its active form, dabigatran--a potent, competitive and reversible DTI. Dabigatran has an advantage over the indirect thrombin inhibitors, unfractionated heparin and low-molecular-weight heparin, in that it inhibits free and fibrin-bound thrombin. The reversible binding of dabigatran may provide safer and more predictable anticoagulant treatment than seen with irreversible, non-covalent thrombin inhibitors, e.g. hirudin. Dabigatran shows a very low potential for drug-drug interactions. However, co-administration of dabigatran etexilate with other anticoagulants and antiplatelet agents can increase the bleeding risk. Although the new agents are pharmacologically better than VKAs--particularly in terms of fixed dosing, rapid onset of action, no INR monitoring and lower risk of drug interactions--there are some differences between them: the bioavailability of dabigatran is lower than rivaroxaban and apixaban, and so the dabigatran dosage required is higher; lower protein binding of dabigatran reduces the variability related to albuminaemia. The risk of metabolic drug-drug interactions also appears to differ between OACs: VKAs > rivaroxaban > apixaban > dabigatran. The convenience of the new OACs has translated into improvements in efficacy and safety as shown in phase III randomized trials. The new anticoagulants so far offer the greatest promise and opportunity for the replacement of VKAs.

Antiplatelet medications and evolving antithrombotic medication

In treatment and prevention of thromboembolic events, the two major classes of anticoagulants are the antiplatelet agents and the antithrombotic agents. The antithrombotic agents have traditionally been heparin and warfarin, both of which were isolated in the 1930s, and have been used effectively since becoming commercially available in treatment and thromboprophylaxis of venous thromboembolic events (VTE). Though effective, they have a narrow therapeutic window and the antithrombotic response is variable, depending on the patient, and requires regular monitoring and adjustment to maintain the necessary therapeutic range. Recently developed novel anticoagulants in the prevention and treatment of VTE are now available and are increasingly encountered in day-to-day practice. A general understanding of these agents is essential in the planning of any interventional procedure in order to optimally balance the risk of hemorrhage, during or after a procedure, with the risk of periprocedural thrombosis.

Extracorporeal therapy for dabigatran removal in the treatment of acute bleeding: a single center experience

BACKGROUND AND OBJECTIVES

Dabigatran is an oral direct thrombin inhibitor that is Food and Drug Administration-approved for prevention of stroke in patients with atrial fibrillation. No antidote is available for reversal of dabigatran's anticoagulant effect. Despite limited clinical data, hemodialysis has been suggested as a strategy to remove dabigatran during acute bleeding. This work presents five cases, in which extracorporeal therapy was performed for dabigatran removal in acutely bleeding patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The series is comprised of five consecutive cases of patients receiving dabigatran 150 mg per os two times daily who were admitted with life-threatening bleeding between March of 2012 and January of 2013. Dabigatran plasma concentrations ranged from 149 to 1200 ng/ml. Treatment included administration of blood products to all patients and then, high-flux intermittent hemodialysis alone or followed by continuous renal replacement therapy.

RESULTS

Dabigatran concentrations decreased by 52%-77% during intermittent hemodialysis but rebounded up to 87% within 2 hours after completion of dialysis. Initiation of continuous renal replacement therapy after intermittent hemodialysis attenuated the rebound effect in one patient and contributed to a reduction in dabigatran concentrations of 81% over 30 hours.

CONCLUSIONS

Extracorporeal therapy lowered dabigatran concentrations, suggesting that it removed the drug and may effectively accelerate total clearance, especially in patients with impaired kidney function. The use of prolonged intermittent hemodialysis or intermittent hemodialysis followed by continuous renal replacement therapy is recommended for the management of life-threatening bleeding in patients receiving dabigatran. The advantage of extracorporeal therapy should be weighed against the risk of bleeding with catheter insertion.

Dabigatran: Is There a Role for Coagulation Assays in Guiding Therapy?

objective:

To determine the usefulness of coagulation assay monitoring for dabigatran etexilate in certain high-risk clinical situations.

DATA SOURCES:

Literature retrieval was accessed through MEDLINE (1948-February 2013), Web of Science (1980-February 2013), International Pharmaceutical Abstracts (1977-February 2013), and Google Scholar using the terms dabigatran, dabigatran etexilate, BIBR 1048, BIBR 953, direct thrombin inhibitor, therapeutic monitoring, and atrial fibrillation. In addition, abstracts presented at the 2011-2012 American Society of Hematology, American College of Cardiology, International Society of Thrombosis and Haemostasis, and European Society of Cardiology annual meetings were reviewed. A search of Clinicaltrials.gov was performed to identify relevant ongoing or completed research.

STUDY SELECTION AND DATA EXTRACTION:

All English-language articles identified from the data sources were evaluated for inclusion. Priority was placed on all data derived from controlled clinical studies.

DATA SYNTHESIS:

Of the 6 published Phase 3 studies, only the RE-LY (Randomized Evaluation of Long-Term Anticoagulation Therapy) trial evaluated the safety and efficacy of dabigatran for the prevention of stroke in patients with nonvalvular atrial fibrillation. Post hoc analyses of the RE-LY trial have provided additional information in special situations. Several published reports highlight the potential for complications with dabigatran, the importance of determining the most optimal candidates, and the need for therapeutic monitoring. Activated partial thromboplastin time and thrombin time are effective qualitative assays for dabigatran. Ecarin clotting time and the dilute thrombin time (ie, Hemoclot direct thrombin inhibitor) assays are suitable for quantitative measurement.

CONCLUSIONS:

The correlation between coagulation-based assays and clinical outcomes among dabigatran-treated patients has not been definitively established. However, coagulation-based assays may be useful in the management of several clinical scenarios.

Traumatic Intracranial Hemorrhage in Patients Taking Dabigatran

BACKGROUND AND IMPORTANCE:

Dabigatran is a direct thrombin inhibitor gaining popularity as a stroke prevention agent in patients with atrial fibrillation. In comparison with warfarin, dabigatran showed superiority in stroke prevention, but lower rates of major hemorrhage and intracerebral hemorrhage. Although warfarin has a well-established reversal strategy, there is far less experience reversing dabigatran.

CLINICAL PRESENTATION:

We present our experience with 3 patients who experienced an intracranial hemorrhage either spontaneously or after low-energy cranial trauma and review the available literature describing dabigatran use in patients with traumatic brain injury.

CONCLUSION:

Intracranial hemorrhage in patients taking anticoagulants and/or antiplatelets can have either a benign or malignant clinical course. At this time, there is little experience with dabigatran reversal; however, several strategies for rapid reversal have been proposed. All patients with intracranial hemorrhage taking dabigatran should be admitted for close neurological monitoring and serial imaging.

New oral anticoagulants in non-valvular atrial fibrillation

Atrial fibrillation (AF) is associated with an increased risk of embolic stroke. Dose-adjusted vitamin K antagonists (VKAs) to a target international normalized ratio (INR) range of 2.0-3.0 reduce the risk of ischemic stroke and are currently recommended in all patients with AF at moderate-high risk for stroke or systemic embolism. However, VKAs have several drawbacks, including unpredictable anticoagulant response, food and drug interactions, need for regular laboratory monitoring and dose adjustment. These limitations prompted the introduction of new oral anticoagulants (NOA) that target thrombin and factor Xa, key-enzymes in the coagulation pathway. NOA have predictable pharmacodynamics, allowing fixed dosing without the need of laboratory monitoring, and have few drug and food interactions. The present review focuses on pharmacological properties, safety, and appropriate clinical use of dabigatran, rivaroxaban and apixaban.

Tutorial in oral antithrombotic therapy: biology and dental implications

Objectives: Recent developments of new direct oral anticoagulants that target specific clotting factors necessitate understanding of coagulation biology. The objective of this tutorial is to offer dental professionals a review of coagulation mechanisms and the pharmacodynamics of the conventional and new oral anticoagulants. Also, we summarized the dental implications of the conventional and new anticoagulants. Method: We searched Medline using search terms “antithrombotic”, “antihemostasis” or “anticoagulation” and combined them with the search results of “dental”, “oral surgery” or “periodontal”. We restricted the results to “human” and “English”. Results: The early coagulation cascade, the new cell-based coagulation model, the pharmacokinetics and pharmacodynamics of conventional antithrombotics, and new oral anticoagulants were reviewed. The new direct factor Xa inhibitors and the direct thrombin inhibitor (s), called direct oral anticoagulants (DOAs) have rapid onset of action, fast elimination on cessation, and fewer drug-drug or drug-food interactions than warfarin. However, the lack of antidotes raises concerns that some dental procedures may trigger serious hemorrhagic events. Additionally, careful perioperative withdrawal and resumption protocols for the DOAs are reviewed, because DOAs’ blood levels are dependent on renal function. Also, various reversal strategies in the event of excessive bleedings are summarized. Perioperative management of dental patients taking new DOAs and conventional oral anticoagulants are also discussed. However, the perioperative strategies for DOAs are yet to be validated in randomized trials.

Key words:Coagulation cascade, cell-based coagulation model, factor Xa inhibitors, direct thrombin inhibitors, prothrombin complex concentrates.

Novel oral anticoagulants: clinical pharmacology, indications and practical considerations

BACKGROUND

Novel oral anticoagulants are approved in several indications: rivaroxaban, apixaban, and dabigatran for the prevention of venous thromboembolism after elective hip or knee replacement surgery, and edoxaban for hip or knee replacement surgery and hip fracture surgery (in Japan only); rivaroxaban for the treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE), and prevention of recurrent DVT and PE; and rivaroxaban, apixaban, and dabigatran for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation. These agents overcome some limitations of traditional anticoagulants, are suggested to have no requirement for routine coagulation monitoring, and are administered orally. Rivaroxaban, apixaban, and dabigatran have different pharmacological characteristics, and guidance is needed on optimum doses and dosing intervals and the effects of renal or hepatic impairment, age, food, and other drugs. Dabigatran has stricter prescribing advice than rivaroxaban or apixaban for patients with moderate-to-severe renal impairment. All three drugs have restrictions on use in patients with hepatic impairment. Apixaban requires twice-daily dosing in all indications, whereas rivaroxaban and dabigatran are dosed once- or twice-daily depending on indication. Although head-to-head comparisons are lacking, the novel oral anticoagulants may show favorable cost-benefit relations compared with traditional vitamin K antagonists or no therapy.

AIM

This review summarizes the pharmacology of rivaroxaban, apixaban, edoxaban, and dabigatran, and the indications for which they are approved. Issues regarding the optimization of the use of these anticoagulants for the management of thromboembolic disorders will also be discussed.

Recent advances in the diagnosis and treatment of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a drug-mediated, prothrombotic disorder caused by immunization against platelet factor 4 (PF4) after complex formation with heparin or other polyanions. After their binding to PF4/heparin complexes on the platelet surface, HIT antibodies are capable of intravascular platelet activation by cross-linking Fcγ receptor IIA leading to a platelet count decrease and/or thrombosis. Diagnosis of HIT is often difficult. This, and the low specificity of the commercially available immunoassays, leads currently to substantial overdiagnosis of HIT. Timing of onset, the moderate nature of thrombocytopenia, and the common concurrence of thrombosis are very important factors, which help to differentiate HIT from other potential causes of thrombocytopenia. A combination of a clinical pretest scoring system and laboratory investigation is usually necessary to diagnose HIT. Although HIT is considered to be a rare complication of heparin treatment, the very high number of hospital inpatients, and increasingly also hospital outpatients receiving heparin, still result in a considerable number of patients developing HIT. If HIT occurs, potentially devastating complications such as life-threatening thrombosis make it one of the most serious adverse drug reactions. If HIT is strongly suspected, all heparin must be stopped and an alternative nonheparin anticoagulant started at a therapeutic dose to prevent thromboembolic complications. However, the nonheparin alternative anticoagulants bear a considerable bleeding risk, especially if given to patients with thrombocytopenia due to other reasons than HIT. While established drugs for HIT are disappearing from the market (lepirudin, danaparoid), bivalirudin, fondaparinux and potentially the new anticoagulants such as dabigatran, rivaroxaban and apixaban provide new treatment options.

Safety of continuous anticoagulation with dabigatran during implantation of cardiac rhythm devices

The perioperative bleeding risk associated with therapeutic anticoagulation at cardiac implantable electronic device implantation has previously been demonstrated to vary by the specific anticoagulant used. Although uninterrupted anticoagulation with warfarin appears to be safe, heparin products have been shown to increase the risk of perioperative bleeding. However, the risk associated with cardiac implantable electronic device implantation with anticoagulation using dabigatran, a novel oral direct thrombin inhibitor, is not known. We performed a prospective observational study of patients receiving dabigatran for anticoagulation who underwent cardiac implantable electronic device implantation from June 2011 through May 2012. The study end points included thromboembolic and bleeding complications within 30 days of surgery. Major bleeding complications were defined as bleeding requiring surgical intervention, prolongation of hospitalization, and discontinuation of the anticoagulant or transfusion of blood products within 30 days of surgery. Minor bleeding complications included the development of a hematoma not requiring additional intervention. The thrombotic end points included stroke, transient ischemic attack, myocardial infarction, pulmonary embolism, and deep vein thrombosis. A total of 25 patients were identified for inclusion. During the index hospitalization, no thromboembolic or bleeding complications developed. No major bleeding complications occurred within 30 days of surgery. One minor bleeding event (4%) occurred within 30 days of surgery in 1 patient who was also receiving dual antiplatelet therapy. In conclusion, although no thromboembolic or major bleeding events were observed, additional studies are required to define the optimal antithrombotic management in the perioperative period.

Dabigatran in the peri-procedural period for radiofrequency ablation of atrial fibrillation: efficacy, safety, and impact on duration of hospital stay

Purpose

Dabigatran is effective for both the prevention of stroke and bleeding in patients with atrial fibrillation (AF). However, the safety and efficacy of the use of dabigatran in the peri-procedural period for radiofrequency catheter ablation (RFCA) of AF is unknown. Therefore, the purpose of this study was to evaluate the safety and efficacy of dabigatran in the peri-procedural period for RFCA of AF and the duration of hospital stay.

Methods

Consecutive patients (n = 227) who underwent RFCA for AF were prospectively analyzed. Peri-procedural anticoagulant therapy with dabigatran (n = 101, D group) was compared with warfarin and heparin bridging (n = 126, W group). Dabigatran was discontinued 12–24 h before and restarted 3 h after the procedure. Warfarin was stopped 3 days before the procedure and unfractionated heparin was administered.

Results

Ischemic stroke occurred in one patient of the D group (0.8 %). There was no significant difference between the two groups in the incidence of major bleeding (three cases of cardiac tamponade in each group and one case of intracranial bleeding in the W group, p = 0.93) or minor bleeding (five cases in the D group vs. five in the W group, p = 0.54). The duration of hospital stay was significantly shorter in the D group than in the W group (7.2 vs. 10.3 days, p = 0.0001).

Conclusions

Peri-procedural anticoagulation therapy with dabigatran for RFCA of AF was equally safe and effective compared with warfarin and heparin bridging. The use of dabigatran for RFCA of AF shortened the duration of hospital stay.