Clinical pharmacokinetics and pharmacodynamics of the oral direct thrombin inhibitor dabigatran etexilate

New oral anticoagulants for stroke prevention in atrial fibrillation: more choices bring more challenges

For patients with atrial fibrillation, anticoagulant therapy is essential to reduce the risk of ischemic stroke that is associated with this arrhythmia. Historically, warfarin has been the preferred treatment for patients at moderate to high risk despite many potential limitations. With the development of newer oral anticoagulants, clinicians now have 3 additional options: dabigatran, rivaroxaban, and apixaban. Although these agents clearly offer some advantages over warfarin, they may not be appropriate for all patients. This article will discuss factors that should be considered when selecting among these various anticoagulants.

Dabigatran bleed risk with closed head injuries: are we prepared?

OBJECT

The direct thrombin inhibitor dabigatran has recently been approved in the US as an alternative to warfarin. The lack of guidelines, protocols, and an established specific antidote to reverse the anticoagulation effect of dabigatran potentially increases the rates of morbidity and mortality in patients with closed head injury (CHI). Confronted with this new problem, the authors reviewed their initial clinical experience.

METHODS

The authors retrospectively reviewed all cases of adult patients (age ≥ 18 years) who sustained CHI secondary to ground-level falls and who presented to the authors' provisional regional Level I trauma center between February 2011 and May 2011. The authors divided these patients into 3 groups based on anticoagulant therapy: dabigatran, warfarin, and no anticoagulants.

RESULTS

Between February 2011 and May 2011, CHIs from ground-level falls were sustained by 5 patients while on dabigatran, by 15 patients on warfarin, and by 25 patients who were not on anticoagulants. The treatment of the patients on dabigatran at the authors' institution had great diversity. Repeat CT scans obtained during reversal showed 4 of 5 patients with new or expanded hemorrhages in the dabigatran group, whereas the warfarin group had 3 of 15 (p = 0.03). The overall mortality rate for patients sustaining CHI on dabigatran was 2 (40%) of 5, whereas that of the warfarin group was 0 (0%) of 15 (p = 0.05).

CONCLUSIONS

It is critical for physicians involved in the care of patients with CHI on dabigatran to be aware of an elevated mortality rate if no treatment protocol or guideline is in place. The authors will soon implement a reversal management protocol for patients with CHI on dabigatran at their institution in an attempt to improve efficacy and safety in their treatment approach.

Subtherapeutic anticoagulation with dabigatran following Roux-en-Y gastric bypass surgery

We report a 66-year-old male with a history of Roux-en-Y gastric bypass surgery who began dabigatran for new onset atrial fibrillation. After 5 weeks of therapy, his transesophageal echocardiogram prior to electrocardioversion showed severe spontaneous echo contrast. Cardioversion was postponed and anticoagulant therapy was continued. The following day, he suffered a thromboembolic stroke. Concern arose that postoperative malabsorption could have resulted in subtherapeutic anticoagulation. This notion was strengthened by a second patient who had subtherapeutic serum levels despite maximal dosing. To the best of our knowledge, we are the first to report impaired absorption of dabigatran following Roux-en-Y gastric bypass surgery. <Learning objective: Dabigatran has a predictable pharmacokinetic profile, allowing for a fixed-dose regimen that does not require frequent monitoring or dietary modifications. However, its absorption in patients who have undergone Roux-en-Y gastric bypass surgery has not been studied. Postoperative malabsoprtion, a major complication following Roux-en-Y gastric bypass surgery, can result in inadequate anticoagulation. As a result of unpredictable absorption, strategies allowing for routine monitoring may be best in this population.>.

Protecting the Brain and the Heart

Novel anticoagulants (NOACs) are the recent therapeutic breakthrough in the prophylaxis of stroke in patients with nonvalvular atrial fibrillation (NVAF). Patients with NVAF seem to have a high atherosclerotic burden, but it has not yet been established whether these agents also protect against cardiovascular disease (CVD). Different NOACs could have cardioprotective properties of different importance, but data come only from indirect comparisons. Patients with NVAF are at risk of stroke when there is concomitant atherosclerosis that also necessitates optimal treatment to reduce CVD risk. Combining antiplatelets with anticoagulants is a common clinical scenario and not always justified by current data and guidelines, putting patients at unnecessary bleeding risk. This review provides current knowledge about the cardioprotective properties of NOACs, the clinical importance of the link between CVD and NVAF, and the pitfalls of combining antiplatelet therapy with warfarin or NOACs.

Hemodialysis for the treatment of pulmonary hemorrhage from dabigatran overdose

Dabigatran is an oral direct thrombin inhibitor indicated for thromboembolism prophylaxis in patients with nonvalvular atrial fibrillation. Since its approval in the United States in 2010, dabigatran-associated hemorrhages have garnered much attention because bleeding rates were higher than initially expected. Additionally, reversing anticoagulation remains challenging. Traditional modes of reversing warfarin-associated coagulopathies are ineffective in reversing anticoagulation from dabigatran. Although hemodialysis is proposed as a method to accelerate dabigatran elimination, evidence supporting its clinical utility remains unproved. We report the case of an 80-year-old man who presented with worsening hemoptysis in the setting of unintentional ingestion of excess dabigatran. Despite transfusion of 2 units of fresh frozen plasma, he continued to bleed, although his international normalized ratio improved from 8.8 to 7.2. He underwent hemodialysis, and serum dabigatran concentration decreased from 1,100 to 18 ng/mL over 4 hours, with an initial extraction ratio of 0.97 and blood clearance of 291 mL/min. Although his serum dabigatran concentration rebounded to 100 ng/mL 20 minutes after the cessation of dialysis, his bleeding stopped and he improved clinically. Hemorrhage in the setting of dabigatran anticoagulation remains a therapeutic predicament. Hemodialysis may play an adjunct role in accelerating the elimination of dabigatran in bleeding patients.

New oral anticoagulants in the treatment of pulmonary embolism: efficacy, bleeding risk, and monitoring

Anticoagulation therapy is mandatory in patients with pulmonary embolism to prevent significant morbidity and mortality. The mainstay of therapy has been vitamin-K antagonist therapy bridged with parenteral anticoagulants. The recent approval of new oral anticoagulants (NOACs: apixaban, dabigatran, and rivaroxaban) has generated significant interest in their role in managing venous thromboembolism, especially pulmonary embolism due to their improved pharmacokinetic and pharmacodynamic profiles, predictable anticoagulant response, and lack of required efficacy monitoring. This paper addresses the available literature, on-going clinical trials, highlights critical points, and discusses potential advantages and disadvantages of the new oral anticoagulants in patients with pulmonary embolism.

Novel oral anticoagulants for stroke prevention in patients with atrial fibrillation: dawn of a new era

Atrial fibrillation (AF) is an important cause of ischemic stroke and is the underlying cause of > 20% of all strokes, with increasing age being a risk factor. Until recently, warfarin was the only available oral anticoagulant used to decrease this risk in patients with AF. However, there are several disadvantages of warfarin use, such as the requirement for monitoring the international normalized ratio, its wide range of drug-food interactions, and its narrow therapeutic index. Thus, there has been a strong impetus for the development of newer oral anticoagulants with predictable pharmacokinetics that obviate the need for monitoring the international normalized ratio. The US Food and Drug Administration has approved a direct thrombin inhibitor (dabigatran) and 2 factor Xa inhibitors (rivaroxaban and apixaban) for stroke prevention in patients with nonvalvular AF. There are several other new oral anticoagulant agents on the horizon, including the factor Xa inhibitor edoxaban. This review article discusses the pharmacological properties, clinical trial data, and practical issues associated with the use of these novel oral anticoagulants.

A review of oral anticoagulants in patients with atrial fibrillation

There is a high prevalence of atrial fibrillation in the United States, particularly in the elderly population. Patients with atrial fibrillation are at an increased risk of stroke and anticoagulant therapy is recommended. However, many eligible patients are not receiving therapy due to limitations and concerns related to the use of the vitamin K antagonist warfarin, such as slow onset of action, variable drug metabolism, risk of bleeding, and requirement for monitoring. Novel oral anticoagulants (NOACs) have been developed and may be used as an alternative to warfarin. This review article summarizes the current clinical trial data for warfarin compared with the NOACs dabigatran (direct thrombin inhibitor), and rivaroxaban and apixaban (factor Xa inhibitors). Dabigatran (150 mg twice daily) demonstrated superiority in reducing the stroke or systemic embolism rate compared with warfarin (1.53% vs 1.69%; P < 0.001). The risk of major bleeding was similar for dabigatran and warfarin (3.32% per year vs 3.57% per year; P = 0.32). Rivaroxaban (20 mg once daily) demonstrated noninferiority in reducing the stroke or systemic embolism rate compared with warfarin (2.1% vs 2.4%; P < 0.001). There was no significant difference between rivaroxaban and warfarin for the risk of major bleeding and clinically relevant nonmajor bleeding (14.9% per year vs 14.5% per year; P = 0.44). Apixaban (5 mg twice daily) demonstrated superiority compared with warfarin in preventing stroke or systemic embolism (1.27% vs 1.60%; P = 0.01). Apixaban significantly reduced major bleeding compared with warfarin (2.13% per year vs 3.09% per year; P < 0.001). Compared with warfarin, all-cause mortality was numerically lower for dabigatran (P = 0.051) and similar for rivaroxaban (P = 0.15). Apixaban demonstrated significantly lower mortality rates compared with warfarin (3.52% vs 3.94%; P = 0.047). All 3 NOACS--dabigatran, rivaroxaban, and apixaban--significantly reduced intracranial hemorrhage compared with warfarin. Novel oral anticoagulants may be a suitable alternative to warfarin for different patient populations due to minimal drug interactions, lower bleeding risk, and no monitoring requirement.

New oral anticoagulants in elderly patients with atrial fibrillation

The prevalence of atrial fibrillation increases with age, augmenting the risk of embolic stroke in elderly individuals. Clinical practice guidelines recommend the long-term use of oral anticoagulation in elderly patients with atrial fibrillation to reduce risk of stroke. Until recently, vitamin K antagonists (eg, warfarin) were the only oral anticoagulants available, but using warfarin in elderly patients can be challenging. Newer oral anticoagulants may offer specific benefits and increased convenience for elderly patients, because they have predictable pharmacologic profiles, a rapid onset of action, a wide therapeutic window, no requirement for routine coagulation monitoring, and fewer and better-defined food and drug interactions compared with warfarin. This review highlights the benefits and challenges of warfarin use in elderly patients with atrial fibrillation and discusses potential efficacy and safety benefits for newer oral agents in these patients. The potential for increased rates of major bleeding in the elderly, particularly those with numerous concomitant medications or renal impairment, also is discussed. Practical considerations for the use of long-term anticoagulation in elderly patients also are discussed.

Acute pulmonary emboli in a patient on long-term dabigatran therapy

OBJECTIVE

To describe the case of a patient who developed acute pulmonary emboli (PE) despite long-term anticoagulation with dabigatran.

CASE SUMMARY

A 69-year-old obese woman was hospitalized for worsening shortness of breath, dyspnea on exertion, and left pleuritic chest pain. On admission, a computed tomography angiogram revealed acute bilateral PE, despite use of dabigatran for atrial fibrillation for approximately 5 years prior to admission. Dabigatran was stopped and therapeutic enoxaparin was initiated concomitantly with warfarin. An investigation into possible causes for the development of the PE, including hypercoagulability, was unrevealing. Since dabigatran should have protected against PE, the patient was questioned regarding adherence to her regimen. She stated that she was adherent but reported using a pillbox. The patient was discharged home on warfarin with an enoxaparin bridge until her international normalized ratio was at least 2.0.

DISCUSSION

The underlying cause for the patient's acute PE is unknown but could possibly be attributed to obesity and reduced mobility. Although dabigatran should have prevented PE, the presence of interacting drugs, patient-specific pharmacokinetics, suboptimal medication storage, and laboratory abnormalities may have resulted in reduced dabigatran exposure and protection. This is a reasonable hypothesis; however, the patient did not develop a stroke while receiving dabigatran.

CONCLUSIONS

Our patient developed acute bilateral PE despite receiving long-term anticoagulation with dabigatran. While it is possible that patient-specific factors resulted in reduced dabigatran exposure and efficacy, conclusions cannot be made.

Intracerebral haemorrhage associated with antithrombotic treatment: translational insights from experimental studies

Little is known about the pathophysiology of intracerebral haemorrhage that occurs during anticoagulant treatment. In observational studies, investigators have reported larger haematoma volumes and worse functional outcome in these patients than in those with intracerebral haemorrhage and a normal coagulation status. The need to prevent extensive haematoma enlargement by rapid reversal of the anticoagulation seems intuitive, although no evidence is available from randomised clinical trials. New oral anticoagulants, such as the direct thrombin inhibitor dabigatran and the factor Xa inhibitor rivaroxaban, have been approved recently; however, intracerebral haemorrhage during dabigatran or rivaroxaban anticoagulation has not been characterised, and whether anticoagulation reversal can be beneficial in this scenario is unknown. In a translational approach, new experimental models have been developed to study anticoagulation-associated intracerebral haemorrhage in more detail and to test treatment strategies. Vitamin k antagonists enlarge haematoma volumes and worsen functional outcome in animal models. Rapid reversal of anticoagulation in the experimental setting prevents prolonged haematoma expansion and improves outcome. The new oral anticoagulants increase intracerbral haemorrhage volumes less than does warfarin. Haemostatic approaches that have been used for vitamin k-associated intracerebral haemorrhage also seem to be effective in intracerebral haemorrhage associated with the new anticoagulants. These experimental studies are valuable for filling gaps in knowledge, but the results need careful translation into routine clinical practice.

Cost-effectiveness of dabigatran compared with warfarin for stroke prevention in patients with atrial fibrillation--a real patient data analysis in a Hong Kong teaching hospital

BACKGROUND

To compare the management cost and cost-effectiveness of dabigatran with warfarin in patients with nonvalvular atrial fibrillation (AF) from the hospital's and patients' perspectives.

HYPOTHESIS

Dabigatran is more cost-effective than warfarin for stroke prevention of AF in Hong Kong.

METHODS

The analysis was performed in conjunction with a drug utilization evaluation of dabigatran study in a teaching hospital in Hong Kong. The study recruited 244 patients who received either dabigatran or warfarin for stroke prevention of AF. A cost-effectiveness analysis was performed and was expressed as an incremental cost-effectiveness ratio (ICER) in averting a cardiac event or a bleeding event. A sensitivity analysis was used on all relevant variables to test the robustness.

RESULTS

From the hospital's perspective, the dabigatran group had a lower total cost of management than that of the warfarin group (median: US$421 vs US$1306, P < 0.001) (US$1 = HK$7.75) and was dominant over warfarin. From the patients' perspective, the total cost of management in the dabigatran group was higher than that in warfarin group (median: US$1751 vs US$70, P < 0.001), and the ICER in preventing a cardiac or bleeding event of dabigatran vs warfarin was estimated at US$68,333 and US$20,500, respectively. If dabigatran was subsidized by the hospital, a higher cost would be incurred by the hospital (median: US$1679 vs US$1306, ICER (cardiac and bleeding events): US$15,163 and US$4549, respectively).

CONCLUSIONS

The study favored dabigatran for stroke prophylaxis in patients with nonvalvular AF in Hong Kong under the current hospital's perspective and provided a reference for further comparisons under patient and subsidization perspectives.

Case report: dabigatran-associated gynecologic bleeding

PURPOSE

The case of a patient who experienced major gynecological bleeding after initiation of dabigatran therapy for atrial fibrillation is reported.

SUMMARY

A 33-year-old Hispanic female with multiple medical problems presented to the emergency department (ED) with a 5-day history of menorrhagia and a 3-day history of dizziness, fatigue, and weakness. Prior to ED presentation, she had been initiated on dabigatran 150 mg twice daily for atrial fibrillation. Four days later, she began having profuse vaginal bleeding. She discontinued all of her home medications including dabigatran, and her bleeding subsided the next day. Upon presentation to the ED, her hemoglobin was 7.1 g/dL, for which she was transfused 2 units of packed red blood cells, increasing her hemoglobin to 9.6 g/dL. Because the patient was in atrial fibrillation, warfarin was initiated once she was clinically stable and she was never restarted on dabigatran. Her hemoglobin was stable throughout admission with no further bleeding. She was discharged on warfarin and closely followed without incident.

CONCLUSION

A 33-year-old Hispanic female with no pre-existing gynecologic abnormalities had a major gynecological bleed shortly after starting dabigatran that resolved after discontinuation.

Effective elimination of dabigatran by haemodialysis. A phase I single-centre study in patients with end-stage renal disease

Dabigatran, a specific, reversible direct thrombin inhibitor, is used to prevent ischaemic and haemorrhagic strokes in patients with atrial fibrillation. As with every anticoagulant, there is a need to rapidly reverse its effects in emergency situations. In an open-label, single-centre phase I study with two fixed multiple dosing periods, we investigated the pharmacokinetics, pharmacodynamics and safety of dabigatran before, during and after 4 hour haemodialysis sessions with either 200 or 400 ml/min targeted blood flow in seven end-stage renal disease patients without atrial fibrillation. Dabigatran was administered over three days in a regimen designed to achieve peak plasma concentrations comparable to those observed in atrial fibrillation patients receiving 150 mg b.i.d. and to attain adequate distribution of dabigatran in the central and peripheral compartments. Plasma concentration-time profiles were similar in both periods on Day 3 (Cmax: 176 and 159 ng/ml). Four hours of haemodialysis removed 48.8% and 59.3% of total dabigatran from the central compartment with 200 and 400 ml/minute targeted blood flow, respectively. The anticoagulant activity of dabigatran was linearly related to its plasma levels. There was a minor redistribution of dabigatran (<16%) after the end of the haemodialysis session. In conclusion, a 4 hour haemodialysis session can rapidly eliminate a substantial amount of dabigatran from the central compartment with a concomitant marked reduction in its anticoagulant activity. There was a clinically negligible redistribution of dabigatran after haemodialysis. These results demonstrate that haemodialysis can be a suitable approach to eliminate dabigatran in emergency situations.

Thrombin inhibitors: surgical considerations and pharmacology

The new thrombin inhibitors have provided an exciting opportunity for effective thromboprophylaxis without some of the disadvantages of the current anticoagulants. These drugs are orally administered, have predictable pharmacokinetics and dose-response, do not require monitoring and have an acceptable safety profile when used appropriately. However, inappropriate prescribing of these drugs may lead to catastrophic consequences. Clinicians need to be aware of some of the drawbacks associated with the use of dabigatran and, in particular, its reduced clearance in the setting of renal failure and the lack of an effective reversing agent when bleeding does occur. In this review, the evidence for efficacy and safety of dabigatran is discussed. We also aim to provide practical clinical advice on the pre- and post-operative management of the elective and emergency surgical patient on dabigatran and provide guidelines for the management of acute haemorrhage in the context of dabigatran therapy.

Implications of new anticoagulants in primary practice

BACKGROUND

Effective prophylaxis and treatment of thromboembolic disorders remain suboptimal in many healthcare systems, partly owing to limitations of traditional anticoagulants. New oral anticoagulants have been developed and among these, rivaroxaban, apixaban and dabigatran etexilate are in the most advanced stage of clinical development.

METHOD

A literature search using the PubMed and ClinicalTrials.gov databases was performed to identify English-language publications. The search was performed up to 31 December 2011 with the terms rivaroxaban OR Xarelto, apixaban OR Eliquis and dabigatran OR Pradaxa. Ongoing, completed and published phase III randomised controlled trials were selected as the primary source of information for the clinical development programme of each drug.

RESULTS

The new oral agents demonstrate several advantages over traditional anticoagulants, including administration at fixed doses and no requirement for routine coagulation monitoring On the basis of phase III clinical trials, rivaroxaban, apixaban and dabigatran etexilate have been approved in many countries for the prevention of venous thromboembolism after hip and knee replacement surgery. Dabigatran etexilate and rivaroxaban have also been approved for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation in Europe and the US. In addition, rivaroxaban has been approved in Europe for the treatment of acute deep vein thrombosis and prevention of recurrent venous thromboembolism. Approval of these agents and postapproval monitoring of their safety and efficacy will have implications for primary care.

CONCLUSION

Rivaroxaban, apixaban and dabigatran etexilate offer the possibility of simplified prevention and treatment strategies for thromboembolic disorders in the outpatient setting.

Drug treatment of acute ischemic stroke

Acute ischemic stroke (AIS) is the fourth leading cause of death and the leading cause of adult disability in the USA. AIS most commonly occurs when a blood vessel is obstructed leading to irreversible brain injury and subsequent focal neurologic deficits. Drug treatment of AIS involves intravenous thrombolysis with alteplase (recombinant tissue plasminogen activator [rtPA]). Intravenous alteplase promotes thrombolysis by hydrolyzing plasminogen to form the proteolytic enzyme plasmin. Plasmin targets the blood clot with limited systemic thrombolytic effects. Alteplase must be administered within a short time window to appropriate patients to optimize its therapeutic efficacy. Recent trials have shown this time window may be extended from 3 to 4.5 hours in select patients. Other acute supportive interventions for AIS include maintaining normoglycemia, euthermia and treating severe hypertension. Urgent anticoagulation for AIS has generally not shown benefits that exceed the hemorrhage risks in the acute setting. Urgent antiplatelet use for AIS has limited benefits and should only promptly be initiated if alteplase was not administered, or after 24 hours if alteplase was administered. The majority of AIS patients do not receive thrombolytic therapy due to late arrival to emergency departments and currently there is a paucity of acute interventions for them. Ongoing clinical trials may lead to further medical breakthroughs to limit the damage inflicted by this devastating disease.

Decrease in the oral bioavailability of dabigatran etexilate after co-medication with rifampicin

AIMS

This study examined the effects of the CYP3A/P-glycoprotein inducer, rifampicin, on the pharmacokinetics of dabigatran following oral administration of the prodrug, dabigatran etexilate.

METHODS

This was an open-label, fixed-sequence, four-period study in healthy volunteers. Subjects received a single dose of dabigatran etexilate 150 mg on day 1, rifampicin 600 mg once daily on days 2-8, and single doses of dabigatran etexilate on days 9, 16 and 23.

RESULTS

Twenty-four subjects were treated, of whom 22 received all treatments. Relative to the reference (single dose of dabigatran etexilate alone; treatment A), administration of dabigatran etexilate following 7 days of rifampicin (treatment B) decreased the geometric mean (gMean) area under the concentration-time curve (AUC(0-∞)) and maximal plasma concentration (C(max)) of total dabigatran by 67 and 65.5%, respectively. The time to peak and the terminal half-life were not affected. The gMean ratio for the primary comparison (treatment B vs. treatment A) was 33.0% (90% confidence interval 26.5, 41.2%) for AUC(0-∞) and 34.5% (90% confidence interval 26.9, 44.1%) for C(max), indicating a significant effect on total dabigatran exposure (total pharmacologically active dabigatran represents the sum of nonconjugated dabigatran and dabigatran glucuronide). After a 7 day (treatment C) or 14 day washout (treatment D), the AUC(0-∞) and C(max) of dabigatran were reduced by 18 and 20%, and by 15 and 20%, respectively, compared with treatment A, which was considered not clinically relevant. The overall safety profile of all treatments was good.

CONCLUSIONS

Administration of rifampicin for 7 days resulted in a significant reduction in the bioavailability of dabigatran, which returned almost to baseline after 7 days washout.

New anticoagulants in atrial fibrillation: an update for clinicians

Anticoagulation is vital for stroke and systemic embolism prevention in patients with atrial fibrillation. Current therapy with the vitamin K inhibitor warfarin has many inherent limitations in clinical practice. With the potential of broadening anticoagulation therapy to a larger population, new classes of anticoagulants have recently emerged with the potential for improved efficacy, safety and convenience. Direct thrombin inhibitor and Factor Xa inhibitor classes are showing promise for both patients and clinicians.

Role of new drugs for management of atrial fibrillation

OBJECTIVE

To evaluate the role of newer agents in the management of atrial fibrillation (AF).

DATA SOURCES

EMBASE and MEDLINE were searched (up to June 2012) combining medication names with atrial fibrillation, humans, clinical trials, and pharmacoeconomic. References of the articles identified and www.clinicaltrials.gov were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

Studies were limited to the English language with clinical or pharmacoeconomic end points followed by the consensus of 3 authors.

DATA SYNTHESIS

Formulated to reduce some of the adverse effects associated with amiodarone by removing the iodine component, dronedarone has improved clinical outcomes over placebo when used in paroxysmal or persistent AF; however, it is less efficacious than amiodarone. Worse outcomes with dronedarone have been seen in patients with heart failure or permanent AF. It has not been compared to antiarrhythmic agents other than amiodarone, and pharmacoeconomic evaluations are lacking. Dabigatran 150 mg is superior to warfarin in preventing stroke or systemic embolism and has been associated with lower rates of vascular-associated mortality. Although the rates of major bleeding were not significantly different between the 2 agents, gastrointestinal bleeding and myocardial infarction occurred more frequently with dabigatran. Dabigatran appears to have the most pharmacoeconomic benefit over warfarin in patients with a higher risk of stroke. Rivaroxaban is noninferior to warfarin for the prevention of stroke and systemic embolism, with no difference in the rates of major bleeding. Cost-effectiveness studies have not been performed with this agent at this time. In patients with AF who were not suitable candidates for warfarin, apixaban is superior to aspirin in preventing stroke or systemic embolism without increasing the risk for major bleeding. Additionally, apixaban is superior to warfarin in preventing stroke or systemic embolism, results in fewer bleeding events, and is associated with lower mortality. Apixaban is not cost-effective against aspirin when used for a short duration but gains superiority with prolonged use or in patients with higher risks of stroke. Additionally, apixaban appears to offer a pharmacoeconomic advantage over warfarin at no to minimal cost. Each new anticoagulant lacks a reversal agent and an assay to detect the presence of the anticoagulant, as well as long-term data when used in the clinical setting.

CONCLUSIONS

Use of dronedarone should be limited to patients with paroxysmal or persistent AF and should not be used in patients with heart failure or with permanent AF. Newer antithrombotic agents appear to be promising alternatives for the prevention of stroke in patients with AF; however, more data are needed to understand their role.

Removal of dabigatran by hemodialysis

Dabigatran is a newly available oral direct thrombin inhibitor approved for anticoagulation therapy to prevent strokes in patients with nonvalvular atrial fibrillation. Unlike warfarin, dabigatran's observed therapeutic window and minimal drug-to-drug interaction suggest that invasive laboratory testing and dose adjustment is not necessary. In circumstances of excessive anticoagulation, such as overdoses, decreased kidney function, or instances of significant bleeding, reversing dabigatran's effects may be necessary. Unlike warfarin, no rapid-acting antidote to reverse the effects of dabigatran is known. However, hemodialysis has been suggested as a method of removing dabigatran and thereby reducing its anticoagulant effect. We describe a case in which hemodialysis was used in an attempt to remove dabigatran in a patient with excessive anticoagulation from dabigatran and severe intracranial hemorrhage. Serial dabigatran levels suggested that hemodialysis removed the drug. However, given the large volume of distribution of dabigatran in the terminal phase of elimination, a rebound in drug level was noted. We suggest that a longer duration of therapy or more continuous modality of hemodialysis may be needed in conjunction with the initial hemodialysis treatment of dabigatran coagulopathy.

Anticoagulation for atrial fibrillation in patients on dialysis: are the benefits worth the risks?

PURPOSE OF REVIEW

Atrial fibrillation is common among patients with end-stage renal disease undergoing hemodialysis. Although oral anticoagulation is recommended for stroke prevention in most patients with atrial fibrillation, limited evidence is available to guide treatment in hemodialysis patients with this arrhythmia. We summarize the available evidence on the epidemiology of atrial fibrillation in dialysis patients and review the data on the effectiveness of oral anticoagulation in this population.

RECENT FINDINGS

Atrial fibrillation is increasingly common in patients undergoing chronic hemodialysis, especially among older patients wherein one in six patients is diagnosed with this arrhythmia. Patients with atrial fibrillation experience double the mortality of otherwise similar patients without it. Few hemodialysis patients with atrial fibrillation receive oral anticoagulation, which is consistently associated with excess risks of hemorrhagic stroke. Observational studies did not detect a beneficial association of oral anticoagulation with the risk of ischemic stroke, with some studies describing higher risks of ischemic stroke among warfarin users. New therapeutic options including one oral direct thrombin inhibitor and two oral factor Xa inhibitors have become available, but were not tested in patients with advanced kidney disease.

SUMMARY

Atrial fibrillation is increasingly common in patients undergoing hemodialysis, yet little is known about the optimal management of these patients. The current evidence does not support net benefits from oral anticoagulation in the dialysis population.

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.

Phase III studies on novel oral anticoagulants for stroke prevention in atrial fibrillation: a look beyond the excellent results

In this overview we address the three phase III studies that compared new oral anticoagulants (dabigatran, rivaroxaban and apixaban) with warfarin in the setting of stroke prevention in atrial fibrillation. Strengths and weaknesses of the studies were examined in detail through indirect comparison. We analyze and comment the inclusion and exclusion criteria, the characteristics of randomized patients, the primary efficacy and safety end points and side effects. All new oral anticoagulants resulted in being non-inferior to vitamin K antagonists in reducing stroke or systemic embolism in patients with atrial fibrillation. Dabigatran 150 mg and apixaban were superior to vitamin K antagonists. Importantly, new oral anticoagulants significantly reduced hemorrhagic stroke in all three studies. Major differences among new oral anticoagulants include the way they are eliminated and side effects. Both dabigatran and apixaban were tested in low- to moderate-risk patients (mean CHADS2 [Congestive heart failure, Hypertension, Age, Diabetes, Stroke] score = 2.1-2.2) whereas rivaroxaban was tested in high-risk patients (mean CHADS2 score = 3.48) and at variance with dabigatran and apixaban was administered once daily. Apixaban significantly reduced mortality from any cause. The choice of a new oral anticoagulant should take into account these and other differences between the new drugs.

Effects of dabigatran in vitro on thrombin biomarkers by Calibrated Automated Thrombography in patients after ischemic stroke

Randomized trials suggest superior and safe stroke prevention in patients with atrial fibrillation after anticoagulation with dabigatran (D) at a 150 mg BID as described in the RE-LY prospective randomized open-label trial when compared to warfarin. Thrombin generation (TG) is a cornerstone of coagulation cascade, and represents a critical biomarker of atherothrombosis. We, therefore, sought to define the effect of D in escalating concentrations on the time course of TG using the Calibrated Automated Thrombogram(®) (CAT) technology in patients after ischemic stroke. Serial plasma samples were obtained from 20 patients with ischemic stroke documented by neuroimaging, who were treated with aspirin for at least 30 days. The impact of 0.1, 0.23, 0.46, 0.69 mM D in platelet-poor plasma (PPP) on TG indices was assessed using fluorogenic substrate CAT device. The following integrated CAT parameters: TGmax, start time (t-start) peak time (t-peak), and mean time (t-mean) were calculated for each D dose and compared with those of the vehicle. Preincubation of PPP with D resulted in dose-dependent significant inhibition of most TG indices. The TGmax was gradually reduced from 447 ± 21 nM at baseline and reach significance for 0.46 mM D (355 ± 44 nM, P = 0.03); and decreased further at 0.69 mM D to 302 ± 27 nM (P = 0.01). The t-peak has been achieved 2-3 times later than after vehicle already at 0.23 nM D. The t-start was delayed 3-4 fold starting from 0.23 mM concentration of D (P < 0.001 for all), but not different from D 0.1 mM (1.5 vs. 1.6; P = 0.34). The t-mean was not significantly affected by D. D in vitro impacts indices of TG predominantly by dose dependent inhibition of endogenous TG, and delayed thrombin production. This preliminary evidence, while intriguing, requires confirmation in post-stroke patients receiving orally dosed D in order to determine whether these findings are clinically relevant.

Stroke prevention in atrial fibrillation: understanding the new oral anticoagulants dabigatran, rivaroxaban, and apixaban

Unlike vitamin K antagonists (VKAs), the new oral anticoagulants (NOACs)-direct thrombin inhibitor, dabigatran, and direct activated factor X inhibitors, rivaroxaban, and apixaban-do not require routine INR monitoring. Compared to VKAs, they possess relatively rapid onset of action and short halflives, but vary in relative degrees of renal excretion as well as interaction with p-glycoprotein membrane transporters and liver cytochrome P450 metabolic enzymes. Recent completed phase III trials comparing NOACs with VKAs for stroke prevention in atrial fibrillation (AF)-the RE-LY, ROCKET AF, and ARISTOTLE trials-demonstrated at least noninferior efficacy, largely driven by significant reductions in haemorrhagic stroke. Major and nonmajor clinically relevant bleeding rates were acceptable compared to VKAs. Of note, the NOACs caused significantly less intracranial haemorrhagic events compared to VKAs, the mechanisms of which are not completely clear. With convenient fixed-dose administration, the NOACs facilitate anticoagulant management in AF in the community, which has hitherto been grossly underutilised. Guidelines should evolve towards simplicity in anticipation of greater use of NOACs among primary care physicians. At the same time, the need for caution with their use in patients with severely impaired renal function should be emphasised.

Anticoagulation Issues in Patients with AF

The evaluation of the risk of stroke for individual patients with atrial fibrillation (AF) is a crucial factor in the decision to provide anticoagulation therapy. Novel oral anticoagulants, as compared with warfarin, are associated with a lower or similar rate of stroke and systemic embolism and a lower rate of hemorrhagic stroke. These drugs are administered at a fixed dose, have a shorter peak action and half-life, and do not require international normalized ratio monitoring. After a successful AF ablation, oral anticoagulation therapy discontinuation seems to be feasible in patients with a CHADS2 score greater than or equal to 2 and normal left atrial (LA) function. However, larger prospective randomized trials are needed to confirm the safety of this strategy.

Coadministration of dabigatran etexilate and atorvastatin: assessment of potential impact on pharmacokinetics and pharmacodynamics

BACKGROUND

Dabigatran etexilate, a novel oral direct thrombin inhibitor, has been approved for prophylaxis of thromboembolism in patients undergoing total knee or total hip replacement, and is under clinical investigation for treatment of venous thromboembolism, prevention of stroke in patients with atrial fibrillation, and the treatment of thromboembolic complications following acute coronary syndromes.

OBJECTIVE

To evaluate the potential impact of atorvastatin coadministration on the pharmacokinetics, pharmacodynamics, and safety of dabigatran etexilate.

METHODS

Healthy male and female volunteers (n = 22) were recruited to this open, randomized, multiple-dose, three-way crossover study. They received dabigatran etexilate 150 mg twice daily on days 1-3 and once daily on day 4, atorvastatin 80 mg once daily on days 1-4, or both treatments together on days 1-4.

RESULTS

Exposure to dabigatran at steady state (area under the drug plasma concentration-time curve at steady state) was reduced by 18% with concomitant atorvastatin administration. An 18% increase in plasma atorvastatin concentration occurred with coadministration of dabigatran etexilate. Exposure to its metabolite 2'-hydroxy-atorvastatin remained essentially unchanged and exposure to 4'-hydroxy-atorvastatin was increased by 15%. The small changes observed are deemed of little clinical relevance given the overall inter-individual variability in the metabolism of atorvastatin. Furthermore, there were no changes in the concentrations of active HMG-CoA reductase inhibitors in plasma following dabigatran etexilate coadministration. Six subjects in the atorvastatin treatment group, six subjects during combination treatment, and eight subjects in the dabigatran treatment group reported adverse events. Most of the adverse events reported were nervous system disorders such as dizziness and headache, and general disorders such as fatigue. All adverse events were resolved at the end of the study.

CONCLUSION

Results of this randomized, open-label, three-way crossover design study in healthy male and female volunteers showed that atorvastatin had no influence on the pharmacokinetic/pharmacodynamic profile of dabigatran, and vice versa, dabigatran etexilate had no impact on the pharmacokinetic/pharmacodynamic profile of atorvastatin. Both drugs were well tolerated when given alone or in combination.

Atraumatic acute carpal tunnel syndrome in a patient taking dabigatran

Acute carpal tunnel syndrome is an uncommon diagnosis most often related to blunt trauma requiring immediate surgical decompression to avoid serious sequelae. Patients who present with bleeding-related acute carpal tunnel syndrome tend to have severe pain, rapid onset of swelling, and neurologic symptoms that appear early and progress rapidly secondary to mass effect. Acute carpal tunnel syndrome can occur in anticoagulated patients spontaneously or after minor trauma. This article describes a case of a 57-year-old man with progressive pain and paresthesias in the median nerve distribution after reaching for a picture frame. He was taking dabigatran, a direct thrombin inhibitor, for atrial fibrillation. He developed acute carpal tunnel syndrome secondary to spontaneous bleeding into the carpal canal and flexor tenosynovium with hematoma formation requiring surgical decompression. He reported immediate pain relief postoperatively, had no further bleeding complications, and regained full median nerve function within 2 months.Dabigatran has gained recent popularity for the treatment of atrial fibrillation. Unlike warfarin, its use does not involve regular laboratory monitoring or dose titration. The risks and benefits of dabigatran should be considered carefully by the prescriber, particularly in patients taking medications that may alter its metabolism. Aspirin and nonsteroidal anti-inflammatory drugs may have effects similar to dabigatran and may increase the risk of bleeding problems. Should acute carpal tunnel syndrome occur, the authors recommend prompt surgical decompression rather than conservative management. The modification of anticoagulant therapy should be considered on a case-by-case basis.

Novel drugs for oral anticoagulation pharmacotherapy

Long-term anticoagulation with warfarin is the mainstay of treatment in patients with diseases with high thromboembolic potential, such as atrial fibrillation. However, warfarin therapy carries a number of inherent limitations, including slow onset and offset of action, interindividual variability, food and drug interactions, lack of selectivity and a narrow therapeutic window. Recently developed oral anticoagulants that selectively block key factors in the coagulation cascade, with no need for monitoring or dose adjustment, have the potential to replace warfarin in clinical practice. The safety and efficacy of these agents in patients with atrial fibrillation, venous thromboembolisms and acute coronary syndromes have been the object of numerous recent large-scale clinical investigations. This article provides an overview of the evidence currently available on the use of novel, orally available, selective anticoagulants in patients at risk for thromboembolic events.

Dabigatran etexilate: a review of its use for the prevention of venous thromboembolism after total hip or knee replacement surgery

Dabigatran etexilate (Pradaxa®, Pradax™, Prazaxa®) is indicated for the primary prevention of venous thromboembolic (VTE) events in adults who have undergone elective total hip replacement (THR) or total knee replacement (TKR) surgery. This article reviews the clinical efficacy and tolerability of oral dabigatran etexilate in patients undergoing major orthopaedic surgery, as well as summarizing its pharmacological properties and results of a cost-utility analysis. The discussion of clinical trial data focuses on comparative trials with the EU approved dosage regimen of once-daily subcutaneous enoxaparin sodium 40 mg. Dabigatran etexilate is an oral prodrug of the potent, rapidly acting, reversible, competitive inhibitor of thrombin, dabigatran. Dabigatran has predictable and consistent anticoagulant effects and does not require routine coagulation monitoring or dose titration. In the large, randomized, double-blind, phase III, noninferiority trials, RE-MODEL, RE-NOVATE and RE-NOVATE II, oral dabigatran etexilate, at dosages of 150 and 220 mg once daily, initiated postoperatively was shown to be noninferior to subcutaneous enoxaparin sodium 40 mg once daily (initiated prior to surgery) with regard to the incidence of the composite of total VTE events and all-cause mortality in patients undergoing TKR or THR surgery. In general, oral dabigatran etexilate was well tolerated in clinical trials of patients undergoing major orthopaedic surgery. There were no significant between-group differences in bleeding complications, including major bleeding, clinically relevant non-major bleeding or minor bleeding between the dabigatran etexilate or enoxaparin sodium groups. In addition, a cost-utility analysis from the perspective of the UK National Health Service indicated that dabigatran etexilate 220 mg once daily is dominant (i.e. more effective and less costly) to enoxaparin sodium 40 mg once daily in patients undergoing THR or TKR. Additional head-to-head comparisons would be beneficial to more definitively position dabigatran etexilate relative to other available oral treatment options for VTE prophylaxis, such as rivaroxaban and apixaban. In the meantime, dabigatran etexilate offers a convenient, effective and generally well tolerated treatment option for the prophylaxis of VTE in patients undergoing TKR and THR surgery.

Determination of the anti-F10a or anti-F2a generation action of rivaroxaban or dabigatran

Dabigatran and rivaroxaban are new oral inhibitors of the thrombin (F2a) and F10a, respectively. Both inhibitors decrease the extrinsic or intrinsic generation of F10a/F2a in plasma. An innovative test for extrinsic F10a/F2a generation is the extrinsic coagulation activity assay (EXCA). With the EXCA the action of all F10a/F2a generation inhibitors can be quantified. The present work aimed to establish the mean therapeutic ranges of these two new drugs, as determined in the EXCA. Forty microlitres reconstituted lyophilized commercial pooled normal plasma, that had been supplemented with 0-0.48 mg/l dabigatran or rivaroxaban, in high-quality polystyrene U-wells (Brand781600), were incubated with 4 μl 1 ng/ml human placental tissue factor in 5% human albumin, 250 mmol/l CaCl2 (EXCA-trigger) for 1 min (EXCA-1) or 2 min (EXCA-2) at 37°C. 80 μl 2.5 mol/l arginine, 0.16% Triton X 100, pH 8.6, were added. After 3 min, 20 μl 1 mmol/l CHG-Ala-Arg-pNA in 1.25 mol/l arginine was added and ΔA/t was determined (37°C). The mean therapeutic range (10-20% EXCA) of dabigatran is approximately 0.05-0.1 mg/l. The mean therapeutic range (10-20% EXCA) of rivaroxaban is approximately 0.13-0.22 mg/l. Mean prophylactic concentrations (20-40% EXCA) are approximately 0.02-0.05 mg/l dabigatran and approximately 0.05-0.13 mg/l rivaroxaban. These are the mean ranges. Individual plasma might well behave differently: either an individual patient could be more sensible or more resistant towards one or both of these drugs. It is suggested to perform EXCA tests for each individual patient to determine the real drug dosage he needs to reach 10-20% of normal EXCA for therapy or 20-40% of normal EXCA for prophylaxis.

No influence of dabigatran anticoagulation on hemorrhagic transformation in an experimental model of ischemic stroke

Background

Dabigatran etexilate (DE) is a new oral direct thrombin inhibitor. Clinical trials point towards a favourable risk-to-benefit profile of DE compared to warfarin. In this study, we evaluated whether hemorrhagic transformation (HT) occurs after experimental stroke under DE treatment as we have shown for warfarin.

Methods

44 male C57BL/6 mice were pretreated orally with 37.5 mg/kg DE, 75 mg/kg DE or saline and diluted thrombin time (dTT) and DE plasma concentrations were monitored. Ischemic stroke was induced by transient middle cerebral artery occlusion (tMCAO) for 1 h or 3 h. We assessed functional outcome and HT blood volume 24 h and 72 h after tMCAO.

Results

After 1 h tMCAO, HT blood volume did not differ significantly between mice pretreated with DE 37.5 mg/kg and controls (1.5±0.5 µl vs. 1.8±0.5 µl, p>0.05). After 3 h tMCAO, DE-anticoagulated mice did also not show an increase in HT, neither at the dose of 37.5 mg/kg equivalent to anticoagulant treatment in the therapeutic range (1.3±0.9 µl vs. control 2.3±0.5 µl, p>0.05) nor at 75 mg/kg, clearly representing supratherapeutic anticoagulation (1.8±0.8 µl, p>0.05). Furthermore, no significant increase in HT under continued anticoagulation with DE 75 mg/kg could be found at 72 h after tMCAO for 1 h (1.7±0.9 µl vs. control 1.6±0.4 µl, p>0.05).

Conclusion

Our experimental data suggest that DE does not significantly increase hemorrhagic transformation after transient focal cerebral ischemia in mice. From a translational viewpoint, this indicates that a continuation of DE anticoagulation in case of an ischemic stroke might be safe, but clearly, clinical data on this question are warranted.