New Anticoagulants

Non-vitamin K antagonist oral anticoagulants in cardiovascular disease management: evidence and unanswered questions

WHAT IS KNOWN AND OBJECTIVE

Anticoagulation is important in the management of cardiovascular disorders; however, traditional anticoagulants such as heparins and vitamin K antagonists (VKAs) have limitations, including parenteral administration with the former and the need for coagulation monitoring and dose adjustments with the latter. Three non-VKA oral anticoagulants (OACs), dabigatran, rivaroxaban and apixaban, are available for the prevention of stroke in patients with atrial fibrillation (AF) and may change clinical practice. This article reviews current knowledge and important unanswered questions on the use of these agents in patients with cardiovascular disease.

METHODS

A literature search was performed using PubMed and the search terms dabigatran, rivaroxaban, apixaban, AF and acute coronary syndrome (ACS). Peer-reviewed, published clinical trials, review articles, relevant treatment guidelines and prescribing information documents were identified and reviewed for relevance.

RESULTS AND DISCUSSION

Dabigatran is an oral direct thrombin inhibitor; rivaroxaban and apixaban are oral direct Factor Xa inhibitors. These agents have a quicker onset and offset of action, more predictable pharmacokinetic and pharmacodynamic profiles, and fewer drug-drug interactions than VKAs, allowing use of fixed doses. For the prevention of stroke in patients with AF, the non-VKA OACs were either non-inferior or superior to warfarin with similar or improved bleeding profiles, particularly with respect to reductions in intracranial haemorrhage. In patients with ACS receiving dual antiplatelet therapy, the addition of rivaroxaban significantly reduced the rate of death from cardiovascular causes, myocardial infarction or stroke without increasing fatal bleeding, but led to higher rates of major bleeding. Dose reductions with non-VKA OACs are mandated in certain circumstances in patients with AF, such as moderate renal impairment. Contraindications include creatinine clearance <15 mL/min (<30 mL/min for dabigatran in Europe and Canada) and moderate or severe hepatic impairment, but patients can be transitioned to other anticoagulants if appropriate. It is unknown which non-VKA OAC is optimal for stroke prevention in patients with AF, although factors such as co-medications (e.g. dabigatran may be preferred if a patient is taking a co-medication that is a strong cytochrome P450 3A4 inhibitor) and renal function (rivaroxaban and apixaban depend less on renal clearance than dabigatran) will be important for individual patients. Addition of rivaroxaban to antiplatelet therapy for prevention of recurrent events in patients with recent ACS is approved in Europe for patients at the highest risk (with elevated cardiac biomarkers) and must take into account the increased risk of major bleeding. Although routine coagulation monitoring is not required, an understanding of which assays are appropriate for each non-VKA OAC and how they are affected is important. In a bleeding emergency, non-specific prohaemostatic agents are suggested to reverse the action of the non-VKA OACs, but more clinical data are needed.

WHAT IS NEW AND CONCLUSION

Non-VKA OACs provide similar or improved efficacy and, on current evidence, improved safety. They provide greater convenience, compared with traditional anticoagulants for the prevention of stroke in patients with AF. Rivaroxaban may be of benefit to selected high-risk patients with ACS. Selection of the most appropriate non-VKA OAC will depend on individual patient factors.

Meta-analysis of randomized controlled trials on risk of myocardial infarction from the use of oral direct thrombin inhibitors

Dabigatran has been associated with greater risk of myocardial infarction (MI) than warfarin. It is unknown whether the increased risk is unique to dabigatran, an adverse effect shared by other oral direct thrombin inhibitors (DTIs), or the result of a protective effect of warfarin against MI. To address these questions, we systematically searched MEDLINE and performed a meta-analysis on randomized trials that compared oral DTIs with warfarin for any indication with end point of MIs after randomization. We furthermore performed a secondary meta-analysis on atrial fibrillation stroke prevention trials with alternative anticoagulants compared with warfarin with end point of MIs after randomization. A total of 11 trials (39,357 patients) that compared warfarin to DTIs (dabigatran, ximelagatran, and AZD0837) were identified. In these trials, patients treated with oral DTIs were more likely to experience an MI than their counterparts treated with warfarin (285 of 23,333 vs 133 of 16,024, odds ratio 1.35, 95% confidence interval 1.10 to 1.66, p = 0.005). For secondary analysis, 8 studies (69,615 patients) were identified that compared warfarin with alternative anticoagulant including factor Xa inhibitors, DTIs, aspirin, and clopidogrel. There was no significant advantage in the rate of MIs with the use of warfarin versus comparators (odds ratio 1.06, 95% confidence interval 0.85 to 1.34, p = 0.59). In conclusion, our data suggest that oral DTIs were associated with increased risk of MI. This increased risk appears to be a class effect of these agents, not a specific phenomenon unique to dabigatran or protective effect of warfarin. These findings support the need for enhanced postmarket surveillance of oral DTIs and other novel agents.

Novel oral anticoagulants for the prevention and treatment of thromboembolism

Over the last 5 years, new oral anticoagulant options, including dabigatran, rivaroxaban and apixaban, have become available. Prior to this, vitamin K antagonists were the sole oral anticoagulants, which have been in use for more than 60 years. These novel agents have been studied in a variety of patient populations, including atrial fibrillation, acute coronary syndrome, treatment of venous thromboembolism and thromboprophylaxis. Compared with standard care, these agents have largely been found to be noninferior or superior for efficacy end points, with similar or improved rates of bleeding. As a result, these agents have become attractive alternatives to vitamin K antagonists for the prevention and treatment of thromboembolic disease. This article provides a summary of clinical trial data to help clinicians determine which agent is most appropriate for a given patient.

Basics of Antithrombotic Therapy for Cardiovascular Disease: Pharmacologic Targets of Platelet Inhibitors and Anticoagulants

Arterial thrombus formation is the common pathophysiologic process of cardiovascular disease manifestations, requiring interplay between platelets and coagulation factors. Current platelet inhibitors block the formation of thromboxane A₂ and interfer with adenosine diphosphate stimulation mediated by the P2Y₁₂ receptor. Novel antiplatelet agents blocking these and other pathways are under clinical development. Thrombin represents a bridge between platelets and coagulation. Indirect and direct thrombin inhibitors are pivotal in clinical settings. Other key coagulation factors include factors IX and X which are therapeutic targets of current and novel anticoagulants. This article reviews the pathophysiology of arterial thrombosis and current and novel antiplatelet and anticoagulant agents.

Recent pharmacological advances for treating venous thromboembolism: are we witnessing the demise of warfarin?

Vitamin K antagonists, such as warfarin, have been the mainstay in treatment and prophylaxis of venous thromboembolism. However, warfarin has many disadvantages including a narrow therapeutic window, numerous potential drug interactions, modulation of effect by alcohol and foods containing vitamin K and genetic variation in metabolism of warfarin, all of which contribute to the unpredictability of therapy. This has provided the impetus for developing new oral anticoagulants with a rapid onset of action, wide therapeutic window, predictable and reversible action, with few drug or dietary interactions, no requirement for routine coagulation monitoring or dose adjustment and acceptable cost. No single agent incorporates all these characteristics, but new factor Xa and direct thrombin inhibitors are being introduced into clinical practice that fulfil some of these aims. Here, we briefly discuss the current practice with its limitations and pitfalls, and then review important trials that have launched new oral anticoagulants into clinical practice.

The new oral anti-coagulants and the phase 3 clinical trials - a systematic review of the literature

Background

Anticoagulation with vitamin K antagonists such as warfarin has historically been used for the long term management of patients with thromboembolic disease. However, these agents have a slow onset of action which requires bridging therapy with heparin and its analogues, which are available only in parenteral route. To overcome these limitations, new oral anticoagulants such as factor Xa inhibitors and direct thrombin inhibitors have been developed. The aim of this article is to systematically review the phase 3 clinical trials of new oral anticoagulants in common medical conditions.

Methods

We searched PubMed (Medline) from January 2007 to February 2013 using “Oral anticoagulants”, “New oral anticoagulants”, “Randomized controlled trial”, “Novel anticoagulants”, “Apixaban”, “Rivaroxaban”, “Edoxaban”, “Dabigatran etexilate”, “Dabigatran” and a combination of the above terms. The available evidence from the phase 3 RCTs was summarized on the basis of individual drug and the medical conditions categorized into “atrial fibrillation”, “acute coronary syndrome”, “orthopedic surgery”, “venous thromboembolism” and “medically ill patients”.

Results

Apixaban, rivaroxaban and dabigatran have been found to be either non-inferior or superior to enoxaparin in prophylaxis of venous thromboembolism in knee and hip replacement with similar bleeding risk, superior to warfarin for stroke prevention in atrial fibrillation with significant reduction in the risk of major bleeding, non-inferior to aspirin for reducing cardiovascular death and stroke in acute coronary syndrome with significant increase in the risk of major bleed. Rivaroxaban and dabigatran are also superior to the conventional agents in the management of symptomatic venous thromboembolism. However, compared to enoxaparin, apixaban and rivaroxaban use lead to significantly increased bleeding risk in medically ill patients. Additional studies evaluating the specific reversal agents of these new drugs for the management of life-threatening bleeding or other adverse effects are necessary.

Conclusion

Considering their pharmacological properties, their efficacy and bleeding complications, the new oral agents offer a net favourable clinical profile in orthopedic surgery, atrial fibrillation, acute coronary syndrome and increase the risk of bleeding in critically ill patients. Further studies are necessary to determine the long term safety and to identify the specific reversal agents of these new drugs.

Factor Xa inhibitors versus vitamin K antagonists for preventing cerebral or systemic embolism in patients with atrial fibrillation

BACKGROUND

Anticoagulant treatment with vitamin K antagonists (VKAs) is aimed at preventing thromboembolic complications and has been the therapy of choice for most people with non-valvular atrial fibrillation (AF) for many decades. A new class of anticoagulants, the factor Xa inhibitors, appear to have several pharmacological and practical advantages over VKAs.

OBJECTIVES

To assess the effectiveness and safety of treatment with factor Xa inhibitors versus VKAs for the prevention of cerebral or systemic embolic events in people with AF.

SEARCH METHODS

We searched the trials registers of the Cochrane Stroke Group and the Cochrane Heart Group (June 2012), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2012, Issue 10), MEDLINE (1950 to April 2013) and EMBASE (1980 to April 2013). In an effort to identify further published, unpublished and ongoing trials we searched trials registers and Google Scholar (July 2012). We also screened reference lists and contacted pharmaceutical companies, authors and sponsors of relevant published trials.

SELECTION CRITERIA

Randomised controlled trials that directly compared the effects of long-term treatment (more than four weeks) with factor Xa inhibitors and VKAs for the prevention of cerebral and systemic embolism in patients with AF. We included patients with and without a previous stroke or TIA.

DATA COLLECTION AND ANALYSIS

The primary efficacy outcome was the composite endpoint of all strokes and other systemic embolic events. Two authors independently assessed trial quality and the risk of bias, and extracted data. We calculated a weighted estimate of the typical treatment effect across trials using the odds ratio (OR) with 95% confidence interval (CI) by means of a fixed-effect model. However, in the case of moderate or high heterogeneity of treatment effects, we used a random-effects model to compare the overall treatment effects and performed a pre-specified sensitivity analysis excluding any fully open-label studies.

MAIN RESULTS

We included data from 42,084 participants randomised into 10 trials. All participants had a confirmed diagnosis of AF (or atrial flutter) and were deemed by the randomising physician to be eligible for long-term anticoagulant treatment with a VKA (warfarin) with a target International Normalised Ratio (INR) of 2.0 to 3.0 in most patients. The included trials directly compared dose-adjusted warfarin with either apixaban, betrixaban, darexaban, edoxaban, idraparinux or rivaroxaban. Four trials were double-masked, five partially-masked (that is different doses of factor Xa inhibitor administered double-masked and warfarin administered open-label) and one was open-label. Median duration of follow-up ranged from 12 weeks to 1.9 years.The composite primary efficacy endpoint of all strokes (both ischaemic and haemorrhagic) and non-central nervous systemic embolic events was reported in nine of the included studies (40,777 participants). Treatment with a factor Xa inhibitor significantly decreased the number of strokes and systemic embolic events compared with dose-adjusted warfarin (OR 0.81, 95% CI 0.72 to 0.91). We also analysed both components of this composite endpoint separately: treatment with a factor Xa inhibitor significantly decreased both the number of ischaemic and haemorrhagic strokes (OR 0.78, 95% CI 0.69 to 0.89) and the number of systemic embolic events (OR 0.53, 95% CI 0.32 to 0.87).All of the included studies (42,078 participants) reported the number of major bleedings. Treatment with a factor Xa inhibitor significantly reduced the number of major bleedings compared with warfarin (OR 0.89, 95% CI 0.81 to 0.98). There was, however, statistically significant and high heterogeneity (I² = 81%) and an analysis using a random-effects model did not show a statistically significant decrease in the number of major bleedings (OR 0.92, 95% CI 0.63 to 1.34). The pre-specified sensitivity analysis excluding open-label studies showed that treatment with a factor Xa inhibitor significantly reduced the number of major bleedings compared with warfarin (OR 0.84, 95% CI 0.76 to 0.92) but moderate heterogeneity was still observed (I² = 65%). A similar sensitivity analysis using a random-effects model did not show a statistically significant decrease in the number of major bleedings in patients treated with factor Xa inhibitors (OR 0.78, 95% CI 0.57 to 1.05). Part of the observed heterogeneity can thus be explained by the increased risk of major bleedings in the factor Xa treatment arm in the single included open-label study, which studied idraparinux. Other heterogeneity might be explained by differences in baseline bleeding risks in the two largest trials of apixaban and rivaroxaban that we included in this review.Data on intracranial haemorrhages (ICHs) were reported in eight studies (39,638 participants). Treatment with a factor Xa inhibitor significantly reduced the risk of ICH compared with warfarin (OR 0.56, 95% CI 0.45 to 0.70). Again, we observed statistically significant heterogeneity (I² = 60%). The pre-specified sensitivity analysis excluding the open-label study showed that treatment with a factor Xa inhibitor significantly reduced the number of ICHs compared with warfarin (OR 0.51, 95% CI 0.41 to 0.64), without any sign of statistical heterogeneity (I² = 0%).The number of patients who died from any cause was reported in six studies (38,924 participants). Treatment with a factor Xa inhibitor significantly reduced the number of all-cause deaths compared with warfarin (OR 0.88, 95% 0.81 to 0.97).

AUTHORS' CONCLUSIONS

Factor Xa inhibitors significantly reduced the number of strokes and systemic embolic events compared with warfarin in patients with AF. Factor Xa inhibitors also seem to reduce the number of major bleedings and ICHs compared with warfarin, though the evidence for a reduction of major bleedings is somewhat less robust. There is currently no conclusive evidence to determine which factor Xa inhibitor is more effective and safer for long-term anticoagulant treatment of patients with AF as head-to-head studies of the different factor Xa inhibitors have not yet been performed.

Anticoagulation in Patients Aged ≥75 years with Atrial Fibrillation: Role of Novel Oral Anticoagulants

Atrial fibrillation (AF) is an important cause of preventable, disabling stroke and is increasingly prevalent with advancing age. As life expectancies increase around the world, AF-related stroke is a growing global public health concern. Most AF patients are elderly (≥75 years old) and increasing age is a consistent independent risk factor for AF-associated stroke. Warfarin anticoagulation is highly effective for stroke prevention in AF patients, but is underutilized especially in the elderly. Although elderly patients are at increased risk of hemorrhage with oral anticoagulants, the benefit for ischemic stroke reduction exceeds the risk of hemorrhage for most elderly patients. Consequently, age alone should not be considered a contraindication for anticoagulation. Novel oral anticoagulants such as dabigatran, rivaroxaban and apixaban are at least as effective as warfarin in preventing strokes in patients with AF. Relative to warfarin, these novel agents reduce the risk of intracranial hemorrhage, the most devastating complication of anticoagulation therapy in elderly AF patients. The novel oral anticoagulants are especially appealing for stroke prevention in elderly patients with AF.

Oral anticoagulants to reduce the risk of stroke in atrial fibrillation: how should a clinician choose?

Atrial fibrillation (AF), a common arrhythmia that occurs with increasing frequency in the aging population, is associated with increased mortality and morbidity. To ensure that patients receive adequate anticoagulant prophylaxis, clinical guidelines for anticoagulation advocate use of validated scoring systems to stratify patients by cardiovascular risk and predict the individual patient's risk of adverse effects of therapy. Recently approved oral anticoagulants-a direct thrombin inhibitor and the factor Xa inhibitors-may offer advantages over the 50-year standard, warfarin, for efficacy, safety, and ease of administration. Clinical trial experience with the newly approved agents and others, yet to be approved, will define their relative value in reducing the risk of thromboembolism associated with AF. This article discusses issues that may help clinicians choose among these newer agents and individualize treatment appropriately.

Rivaroxaban and other non-vitamin K antagonist oral anticoagulants in the emergency treatment of thromboembolism

Pulmonary embolism (PE) is potentially fatal and often requires emergency management. Because PE associated with shock and/or hypotension carries a high risk of sudden death, emergency clinicians must rapidly make a diagnosis and initiate appropriate therapeutic strategies, usually involving anticoagulant treatment. Traditional anticoagulants, such as heparins and vitamin K antagonists, although effective and recommended by guidelines, are associated with limitations. Several targeted, orally administered anticoagulants that may overcome some of these constraints have been developed recently and undergone analysis in randomised, phase III clinical trials. Rivaroxaban, a direct factor Xa inhibitor, was non-inferior to standard therapy with enoxaparin plus a vitamin K antagonist for the prevention of recurrent, symptomatic venous thromboembolism (VTE) in patients with acute PE and led to a 50% reduction in major bleeding. Dabigatran, a direct thrombin inhibitor, was also non-inferior to standard therapy for the prevention of recurrent VTE or VTE-related death when given after a parenteral anticoagulant and had a similar incidence of major bleeding. The results of a phase III study of apixaban, another direct factor Xa inhibitor, for the acute treatment of VTE are expected in the near future. Rivaroxaban is now approved in Europe and the US for the treatment of acute PE and prevention of recurrent VTE. This article reviews the current guidance on the treatment of PE with special focus on the emergency setting, and considers data regarding rivaroxaban and the other non-vitamin K antagonist oral anticoagulants and their potential role, including patients who are and are not appropriate for treatment with these agents. Issues such as drug interactions, reversal of anticoagulant effect and coagulation monitoring are also discussed.

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.

Blocking direct inhibitor bleeding

In this issue of Blood, Schiele et al report the development of a monoclonal antibody that reverses the anticoagulant effect of the direct thrombin inhibitor dabigatran.

Laboratory assessment of rivaroxaban: a review

Research into new anticoagulants for preventing and treating thromboembolic disorders has focused on targeting single enzymes in the coagulation cascade, particularly Factor Xa and thrombin, inhibition of which greatly decreases thrombin generation. Based on the results of phase III clinical trials, rivaroxaban, a direct Factor Xa inhibitor, has been approved in many countries for the management of several thromboembolic disorders. Owing to its predictable pharmacokinetic and pharmacodynamic characteristics, fixed-dose regimens are used without the need for routine coagulation monitoring. In situations where assessment of rivaroxaban exposure may be helpful, anti-Factor Xa chromogenic assays (in tandem with standard calibration curves generated with the use of rivaroxaban calibrators and controls) could be used. It is important to note that test results will be affected by the timing of blood sampling after rivaroxaban intake. In addition, the anti-Factor Xa method measures the drug concentration and not the intensity of the drug’s anticoagulant activity, and a higher than expected rivaroxaban plasma level does not necessarily indicate an increased risk of bleeding complications. Therefore, clinicians need to consider test results in relation to the pharmacokinetics of rivaroxaban and other patient risk factors associated with bleeding.

Venous thromboembolism management: where do novel anticoagulants fit?

OBJECTIVE

To review novel oral anticoagulant (NOAC) trials in the treatment of venous thromboembolism (VTE) and the possible use of risk-stratification tools to guide their use in practice.

SCOPE

MEDLINE and Cochrane databases were searched to identify relevant journal articles published from January 1982 to February 2013. Additional references were obtained from articles extracted during the database search.

FINDINGS

NOACs have been developed to optimize VTE management and overcome the limitations of heparin and vitamin K antagonists (VKA). The AMPLIFY and EINSTEIN trials of apixaban and rivaroxaban, respectively, investigated single-drug management of VTE, whereas the edoxaban Hokusai-VTE trial and dabigatran RE-COVER and RE-COVER II trials investigated the use of NOACs with a heparin lead-in. The AMPLIFY and Hokusai-VTE trials are ongoing but the EINSTEIN and RE-COVER trials have demonstrated that rivaroxaban and dabigatran, respectively, are non-inferior to parenteral anticoagulants and warfarin in the management of VTE. Differences in study design complicate the application of study results to clinical practice. There are multiple validated DVT protocols that effectively and safely treat patients in outpatient settings. The pulmonary embolism (PE) severity index (PESI), simplified PESI (sPESI), and other prognostic tools have been used to risk stratify patients with PE by estimating mortality risk to guide outpatient eligibility.

CONCLUSIONS

NOACs provide physicians with new therapeutic options in the management of VTE. While heparin and VKAs compose the current standard treatment for VTE, their use will likely disappear as physicians grow comfortable with the adoption of NOACs. As studies have not clearly defined the efficacy of these agents in certain patient populations, further data in special patient populations and risk stratification through the use of VTE severity scores could potentially be adapted to guide anticoagulant management and outpatient treatment eligibility.

New oral anticoagulants increase risk for gastrointestinal bleeding: a systematic review and meta-analysis

BACKGROUND & AIMS

A new generation of oral anticoagulants (nOAC), which includes thrombin and factor Xa inhibitors, has been shown to be effective, but little is known about whether these drugs increase patients' risk for gastrointestinal bleeding (GIB). Patients who require OAC therapy frequently have significant comorbidities and may also take aspirin and/or thienopyridines. We performed a systematic review and meta-analysis of the risk of GIB and clinically relevant bleeding in patients taking nOAC.

METHODS

We queried MEDLINE, EMbase, and the Cochrane library (through July 2012) without language restrictions. We analyzed data from 43 randomized controlled trials (151,578 patients) that compared nOAC (regardless of indication) with standard care for risk of bleeding (19 trials on GIB). Odds ratios (ORs) were estimated using a random-effects model. Heterogeneity was assessed with the Cochran Q test and the Higgins I(2) test.

RESULTS

The overall OR for GIB among patients taking nOAC was 1.45 (95% confidence interval [CI], 1.07-1.97), but there was substantial heterogeneity among studies (I2, 61%). Subgroup analyses showed that the OR for atrial fibrillation was 1.21 (95% CI, 0.91-1.61), for thromboprophylaxis after orthopedic surgery the OR was 0.78 (95% CI, 0.31-1.96), for treatment of venous thrombosis the OR was 1.59 (95% CI, 1.03-2.44), and for acute coronary syndrome the OR was 5.21 (95% CI, 2.58-10.53). Among the drugs studied, the OR for apixaban was 1.23 (95% CI, 0.56-2.73), the OR for dabigatran was 1.58 (95% CI, 1.29-1.93), the OR for edoxaban was 0.31 (95% CI, 0.01-7.69), and the OR for rivaroxaban was 1.48 (95% CI, 1.21-1.82). The overall OR for clinically relevant bleeding in patients taking nOAC was 1.16 (95% CI, 1.00-1.34), with similar trends among subgroups.

CONCLUSIONS

Studies on treatment of venous thrombosis or acute coronary syndrome have shown that patients treated with nOAC have an increased risk of GIB, compared with those who receive standard care. Better reporting of GIB events in future trials could allow stratification of patients for therapy with gastroprotective agents.

Open-label, randomized study of the effect of rivaroxaban with or without acetylsalicylic acid on thrombus formation in a perfusion chamber

INTRODUCTION

Rivaroxaban, a direct factor Xa inhibitor, has demonstrated effectiveness for the management of both venous and arterial thrombosis. This study was designed to investigate the antithrombotic effect of rivaroxaban, with or without acetylsalicylic acid (ASA), in an ex vivo perfusion chamber at both low and high shear rates.

MATERIALS AND METHODS

Healthy subjects (N=51) were enrolled in a randomized, crossover (rivaroxaban 5, 10 or 20mg with or without ASA), and parallel-group (compared with ASA plus clopidogrel) study. Thrombi formed on pig aorta strips were measured after a 5-minute perfusion at low and high shear rates with blood from the subjects by measuring D-dimer concentration (for fibrin deposition) and P-selectin content (for platelet deposition).

RESULTS

ASA alone had no impact on thrombus D-dimer levels, whereas rivaroxaban alone at peak concentrations decreased D-dimer levels by 9%, 84% and 65% at low shear rate and 37%, 73% and 74% at high shear rate after doses of 5, 10 and 20mg, respectively. Steady-state ASA plus rivaroxaban 5mg caused a greater reduction in D-dimer levels (63%) than monotherapy at low shear rate. Co-administration of ASA with clopidogrel was associated with a 30% decrease in D-dimer levels at low shear rate and a 14% decrease at high shear rate. No conclusive effect on P-selectin content was observed across the treatment groups.

CONCLUSIONS

Rivaroxaban dose-dependently inhibited ex vivo thrombus formation under low and high shear rates. Co-administration of ASA had an additional effect on the antithrombotic action of low-dose rivaroxaban.

Managing New Oral Anticoagulants in the Perioperative and Intensive Care Unit Setting

Managing patients in the perioperative setting receiving novel oral anticoagulation agents for thromboprophylaxis or stroke prevention with atrial fibrillation is an important consideration for clinicians. The novel oral anticoagulation agents include direct Factor Xa inhibitors rivaroxaban and apixaban, and the direct thrombin inhibitor dabigatran. In elective surgery, discontinuing their use is important, but renal function must also be considered because elimination is highly dependent on renal elimination. If bleeding occurs in patients who have received these agents, common principles of bleeding management as with any anticoagulant (including the known principles for warfarin) should be considered. This review summarizes the available data regarding the management of bleeding with novel oral anticoagulation agents. Hemodialysis is a therapeutic option for dabigatran-related bleeding, while in vitro studies showed that prothrombin complex concentrates are reported to be useful for rivaroxaban-related bleeding. Additional clinical studies are needed to determine the best method for reversal of the novel oral anticoagulation agents when bleeding occurs.

What did we learn from new oral anticoagulant treatment?

Orally active direct inhibitors of thrombin and factor Xa have now been approved for treatment or prevention of deep vein thrombosis,and stroke associated with atrial fibrillation. The factor Xa inhibitor, rivaroxaban, has shown promising results in the treatment of acute coronary syndrome but is not yet approved for that indication. These agents share a rapid onset and are cleared with half lives of approximately 10 hours. At present there is no approved antidote for either class of anticoagulant, making the treatment of life-threatening bleeding episodes problematic. These agents have fewer drug interactions than warfarin, have a predictable clearance, and hence do not require monitoring. Patients with renal insufficiency have delayed clearance and hence may have elevated levels of the drug leading to increased risk of bleeding.

Potential role of new anticoagulants for prevention and treatment of venous thromboembolism in cancer patients

Venous thromboembolism (VTE), encompassing deep vein thrombosis and pulmonary embolism, represents a major cause of morbidity and mortality in patients with cancer. Low molecular weight heparins are the preferred option for anticoagulation in cancer patients according to current clinical practice guidelines. Fondaparinux may also have a place in prevention of VTE in hospitalized cancer patients with additional risk factors and for initial treatment of VTE. Although low molecular weight heparins and fondaparinux are effective and safe, they require daily subcutaneous administration, which may be problematic for many patients, particularly if long-term treatment is needed. Studying anticoagulant therapy in oncology patients is challenging because this patient group has an increased risk of VTE and bleeding during anticoagulant therapy compared with the population without cancer. Risk factors for increased VTE and bleeding risk in these patients include concomitant treatments (surgery, chemotherapy, placement of central venous catheters, radiotherapy, hormonal therapy, angiogenesis inhibitors, antiplatelet drugs), supportive therapies (ie, steroids, blood transfusion, white blood cell growth factors, and erythropoiesis-stimulating agents), and tumor-related factors (local vessel damage and invasion, abnormalities in platelet function, and number). New anticoagulants in development for prophylaxis and treatment of VTE include parenteral compounds for once-daily administration (ie, semuloparin) or once-weekly dosing (ie, idraparinux and idrabiotaparinux), as well as orally active compounds (ie, dabigatran, rivaroxaban, apixaban, edoxaban, betrixaban). In the present review, we discuss the pharmacology of the new anticoagulants, the results of clinical trials testing these new compounds in VTE, with special emphasis on studies that included cancer patients, and their potential advantages and drawbacks compared with existing therapies.

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.

The new oral anticoagulants in clinical practice

Vitamin K antagonists were the only class of oral anticoagulants available to clinicians for decades. However, with the US Food and Drug Administration approval of new oral anticoagulants, such as dabigatran, rivaroxaban, and apixaban, clinicians now have a broader choice. Given the recent approval and availability of these medications, several questions arise while deciding which of them would be best suited for a particular patient. This article provides a concise review for clinicians entailing the main studies that evaluated the efficacy and safety of these drugs, their pharmacokinetic and pharmacodynamic properties, and a practical approach to their clinical use. For this review, we conducted searches of PubMed and MEDLINE for articles published between January 1, 2000, and January 30, 2013, using the following search terms: oral anticoagulants, dabigatran, apixaban, rivaroxaban, novel anticoagulants, bleeding complications, management of bleeding complications, pharmacodynamics, and pharmacokinetics. Studies published in English were selected for inclusion in this review, as were additional articles identified from bibliographies.

Single-dose TB-402 or rivaroxaban for the prevention of venous thromboembolism after total hip replacement. A randomised, controlled trial

TB-402 is a long-acting monoclonal antibody that partially inhibits factor VIII. A single administration of TB-402 was effective and well-tolerated for the prevention of venous thromboembolism (VTE) after total knee replacement. In this study, the efficacy and safety of a single administration of TB-402 for the extended prophylaxis of VTE after total hip replacement (THR) was investigated. This was a phase II, randomised, active-controlled, double-blind study that included patients undergoing elective THR surgery. Patients were randomised to TB-402 25 mg or TB-402 50 mg, administered as a single intravenous administration 2-4 hours postoperatively, or to rivaroxaban 10 mg once daily for 35 days. The primary efficacy outcome was total VTE defined as symptomatic VTE and asymptomatic deep-vein thrombosis (DVT) detected by bilateral venography at day 35. The principal safety outcome was the incidence of major bleeding and clinically relevant non-major bleeding until day 35. Total VTE was similar in all groups: 5.3% (95%CI 2.9-9.6), 5.2% (95%CI 2.8-9.3) and 4.7% (95%CI 2.5-8.7) for TB-402 25 mg, TB-402 50 mg and rivaroxaban, respectively. All were asymptomatic DVTs. Major or clinically relevant non-major bleedings were observed in 5.8% (95%CI 3.3-9.9), 7.2% (95%CI 4.4-11.6) and 1.4% (95%CI 0.5-4.2) for TB-402 25 mg, TB-402 50 mg and rivaroxaban, respectively. In conclusion, TB-402, administered as a single postoperative dose, had a similar efficacy compared to rivaroxaban for the prevention of VTE after THR. The incidence of major and clinically relevant non-major bleeding was higher in the TB-402 groups than in the rivaroxaban group.

Interplay between coagulation and vascular inflammation in sickle cell disease

Sickle cell disease is the most common inherited haematological disorder that leads to the irreversible damage of multiple organs. Although sickling of red blood cells and vaso-occlusion are central to the pathophysiology of sickle cell disease, the importance of haemolytic anaemia and vasculopathy has been recently recognized. A hypercoagulable state is another prominent feature of sickle cell disease and is mediated by activation of both intrinsic and extrinsic coagulation pathways. Growing evidence demonstrates that coagulation may not only contribute to the thrombotic complications, but also to vascular inflammation associated with this disease. This article summarizes the role of vascular inflammation and coagulation activation, discusses potential mechanisms responsible for activation of coagulation and reviews recent data demonstrating the crosstalk between coagulation and vascular inflammation in sickle cell disease.

Medical management of venous thromboembolism: what the interventional radiologist needs to know

Deep vein thrombosis and pulmonary embolism are considered manifestations of the same pathophysiological process and are together referred to as venous thromboembolism (VTE). VTE is a common disorder with an incidence of 1 to 3 in 1000 in the general population. It is estimated that the incidence of VTE is likely to increase as the average life expectancy of the U.S. population increases. Treatment of VTE consists of anticoagulation; the duration of anticoagulation is largely determined by the circumstances surrounding development of the thrombotic event. Vitamin K antagonists, the only oral anticoagulants approved for treatment of VTE in the United States, have several drawbacks and therefore new oral anticoagulants are currently in various stages of development. This review focuses on the risk factors for VTE and the approach to determining the duration of anticoagulation in patients with VTE. Results of clinical trials on the new oral anticoagulants that may soon be licensed for the treatment of VTE are also discussed.

What NPs need to know about anticoagulation therapy

Venous thromboembolism (VTE) refers to pulmonary embolism and deep venous thrombosis. Anticoagulation is the cornerstone of management for patients with VTE. This review will discuss current anticoagulation guidelines.

New oral anticoagulants: which one should my patient use?

The new oral anticoagulants are rapidly replacing warfarin for several indications. In contrast to warfarin, which lowers the functional levels of all of the vitamin K-dependent clotting factors, the new agents target either factor Xa or thrombin. With targeted inhibition of coagulation, the new oral anticoagulants have pharmacologic and clinical features that distinguish them from warfarin. Focusing on these features, this paper (a) compares the pharmacology of the new oral anticoagulants with that of warfarin (b) identifies the class effects of these drugs and their differentiating features, (c) reviews their current indications, and (d) uses this information to help clinicians make informed decisions regarding the choice of the right anticoagulant for the right patient.

[New advances in anticoagulation: is it time to forget about heparin and vitamin K antagonists? Yes]

For the last 60 years, heparin and vitamin K antagonists have been the cornerstone of anticoagulation. Nowadays, the new anticoagulants, such as dabigatran, rivaroxaban and apixaban, show potential advantages over classical treatments. These agents inhibit specific coagulation factors and are administered orally at fixed doses. Furthermore, heparin and vitamin K antagonists have a fast onset of action, short-duration and predictable therapeutic effects. No interactions with foods have been described, although some drug-drug interactions have been reported. At the moment, no antidotes are available. However, due to the short half-life of these agents, antidotes are less essential. The new anticoagulants are at least as effective and safe as traditional treatments in the prevention of venous thromboembolism after orthopedic surgery, as well as in the prevention of stroke and systemic embolism in non-valvular atrial fibrillation. Dabigatran and rivaroxaban have also been shown to be effective in the treatment of acute venous thromboembolism. Due to their properties, these drugs could gradually replace heparin and especially vitamin K antagonists. Hopefully, many of our patients will be able to discontinue classical anticoagulant treatment and others will never begin it.

The role of anticoagulation clinics in the era of new oral anticoagulants

Anticoagulation Clinics (ACs) are services specialized in management of patients on anticoagulant treatment. At present, ACs manage patients chiefly on antivitamin K antagonists (AVKs), but patient population has already changed in the last few years, because of an increase of treatments with other anticoagulant drugs, which require different management systems. The strong increase in the number of patients at AC, mainly on long-term treatment, has determined the development of web management, through telemedicine systems, improving the quality of life and maintaining the same clinical quality levels. New oral anticoagulants (NOAs) have shown to be as effective as AVK antagonists in stroke prevention in atrial fibrillation and for treatment of venous thromboembolism in addition to VTE prophylaxis in orthopaedic surgery, when administered at a fixed dose, but patient adherence and compliance are crucial for good quality treatment. At present, lacking data from the real world, an oversimplification of treatment with NOAs could cause unjustified risks for patients and also a possible future underuse of good drugs. For these reasons the vigilance must be high and ACs can have a crucial role in defining which is the best management for NOA patients and how to do it, as it happened for AVKs.

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.

New insights into the mechanisms of venous thrombosis

Venous thrombosis is a leading cause of morbidity and mortality in industrialized countries, especially in the elderly. Many risk factors have been identified for venous thrombosis that alter blood flow, activate the endothelium, and increase blood coagulation. However, the precise mechanisms that trigger clotting in large veins have not been fully elucidated. The most common site for initiation of the thrombus appears to be the valve pocket sinus, due to its tendency to become hypoxic. Activation of endothelial cells by hypoxia or possibly inflammatory stimuli would lead to surface expression of adhesion receptors that facilitate the binding of circulating leukocytes and microvesicles. Subsequent activation of the leukocytes induces expression of the potent procoagulant protein tissue factor that triggers thrombosis. Understanding the mechanisms of venous thrombosis may lead to the development of new treatments.

Antidote strategies to reverse anticoagulation with TB-402, a long-acting partial inhibitor of factor VIII

BACKGROUND

TB-402 is a partially inhibiting antibody of factor VIII that is under development as a long-acting anticoagulant.

PATIENTS AND METHODS

The reversibility of FVIII inhibition by TB-402 was evaluated in vitro after spiking with recombinant human FVIII (rhFVIII), human plasma-derived FVIII (hpdFVIII), recombinant activated human FVII (rhFVIIa), FVIII inhibitor bypassing activity (FEIBA), and prothrombin complex concentrate (PCC). Twelve subjects were randomized to placebo or 35 or 70 IU kg(-1) rhFVIII 48 h after a single dose of 620 μg kg(-1) TB-402. TB-402 concentrations, FVIII activity (FVIII:C), activated partial thromboplastin time (APTT) and thrombin generation were measured over a period of 8 weeks.

RESULTS

In spiked samples, TB-402 inhibited FVIII:C by 30%, prolonged APTT by 4.5 s, and reduced the peak height in the thrombin generation assay to 56% ± 13% of the control value. In the presence of 10 μg mL(-1) TB-402, rhFVIII restored FVIII:C and APTT to the values obtained in the absence of TB-402. The inhibitory effect of TB-402 on thrombin generation was entirely reversed by rhFVIII, hpdFVIII, rhFVIIa, FEIBA, and PCC. In men, the mean half-life (t(1/2) ) of TB-402 was 14.2 days. TB-402 lowered the endogenous thrombin potential by 23% for ~ 35 days. Infusion of 35 IU kg(-1) rhFVIII had a marginal effect, whereas 70 IU kg(-1) rhFVIII restored FVIII:C, reduced APTT back to baseline for 9 h, and restored thrombin generation for ~ 3 h.

CONCLUSIONS

TB-402 resulted in a stable long-term anticoagulant effect. rhFVIII and other procoagulants counteracted the effect of TB-402 temporarily, and may be effective antidotes for future clinical practice.

[Management of direct action oral anticoagulants in the peri-operative period and invasive techniques]

The new direct-acting oral anticoagulants (ACOD) in patients on prolonged treatment require the need to balance the risk of haemorrhage by administering them against the risk of thrombosis on withdrawing them. Recommendations for their management are proposed in the present article: A) Thromboprophylaxis and general anaesthesia: the performing of regional anaesthesia if administered with an ACOD as thromboprophylaxis requires some safety intervals based on their pharmacokinetic parameters; B) Management of ACOD in elective surgery: in patients with normal renal function and a low haemorrhage/thrombosis risk, stop the ACOD two days before the surgery; it the haemorrhage/thrombosis risk is high and/or renal function is impaired, therapy with a low molecular weight heparin is proposed from 5 days prior to the surgery, and C) Management of ACOD in urgent surgery and associated haemorrhage: the systematic prophylactic administration of haemostatics is recommended. In the event of acute bleeding that may place the life of the patient at risk (due to volume or location), the administration of concentrated prothrombin complex, fresh plasma, or factor VIIa, must be assessed, together with general control measures of acute haemorrhage. These recommendations should be considered in the context of the use drugs that do have a specific antidote, where their monitoring by the usual coagulation tests is not routine, and with those in which there is limited experience. We believe they need to be reviewed in the future, depending on further studies and clinical experience obtained.

Which risk factors are more associated with ischemic stroke than intracerebral hemorrhage in patients with atrial fibrillation?

BACKGROUND AND PURPOSE

The decision to prescribe oral anticoagulant therapy in patients with atrial fibrillation is based on an assessment of the competing risks of ischemic stroke and major bleeding, of which intracerebral hemorrhage (ICH) is the most important type. We sought to determine the comparative importance of risk factors for ischemic stroke and ICH in patients with acute stroke and atrial fibrillation with particular emphasis on risk factors common to both stroke types.

METHODS

Consecutive patients with acute ischemic stroke or ICH and atrial fibrillation included in the Registry of the Canadian Stroke Network constituted the cohort. Multivariable logistic regression analysis was used to determine the association between baseline risk factors and presentation with ICH versus ischemic stroke. Risk factors included: (1) those previously reported to be risk factors for both ischemic stroke and major bleeding (particularly ICH) ("shared" risk factors, including age, alcohol, hypertension, diabetes mellitus, renal impairment, prior stroke/transient ischemic attack and preadmission dementia); and (2) other risk factors associated with either stroke subtype alone.

RESULTS

A total of 3197 patients presented with atrial fibrillation and acute stroke, of which 12.2% presented with ICH. Of the "shared" risk factors, age (OR, 1.19; 95% CI, 1.06-1.34 per decade) and prior stroke/transient ischemic attack (OR, 1.45; 95% CI, 1.12-1.87) were more associated with ischemic stroke than ICH, whereas a history of hypertension (OR, 0.89; 95% CI, 0.68-1.17), diabetes mellitus (OR 1.23; 95% CI, 0.92-1.64), renal impairment (OR, 1.28; 95% CI, 0.95-1.71), and alcohol intake were not more strongly associated with either stroke subtype.

CONCLUSION

Of the risk factors known to be associated with both ischemic stroke and ICH in patients with atrial fibrillation, we found that none had a stronger association with ICH. Older age was more strongly associated with ischemic stroke than ICH.

Breakthroughs in anticoagulation: advent of the oral direct factor Xa inhibitors

The oral direct factor Xa inhibitors include rivaroxaban and apixaban that recently have been evaluated comprehensively in multiple randomized clinical trials. Based on the efficacy and safety data from these trials, these novel anticoagulants are disseminating throughout clinical practice for thromboprophylaxis in major lower-extremity joint replacement, acute medical illness, atrial fibrillation, and acute coronary syndromes. The advantages of the xabans over vitamin K antagonists include no requirement for routine anticoagulation monitoring as well as a fast and reliable onset of action. The first perioperative limitation of the xabans is the lack of a routine coagulation test for monitoring their anticoagulant effect in scenarios, such as the timing of surgical procedures, the reversal of xaban-related bleeding, and the conduct of regional anesthesia. A second perioperative limitation is the lack of fully validated clinical reversal agents although prothrombin complex concentrate, recombinant factor VIIa, and factor X concentrate are options for xaban reversal in life-threatening bleeding scenarios. Given their clinical efficacy and advantages, further xabans are in clinical development, with edoxaban already in phase III clinical trials. Although the xabans have ushered in a new paradigm for clinical anticoagulation, further clinical trials are indicated to refine their clinical indications even further, such as anticoagulation for patients with mechanical heart valves.