Apixaban-Associated Intracranial Hemorrhage in a Patient With Elevated International Normalized Ratio

Apixaban has been associated with prolongation of the international normalized ratio (INR), but data surrounding the extent of elevation and its clinical significance are limited. Due to interaction between apixaban and the prothrombin assay, elevations in INR in patients receiving apixaban are common and not always grounds for concern. However, in high risk patients, elevations can represent a need for closer monitoring. This case summarizes an 82-year-old woman with a history of atrial fibrillation and left middle cerebral artery strokes with no residual deficits. She presented with right-sided hemiparesis and aphasia and underwent a mechanical thrombectomy with TICI 2b recanalization of a left M1 occlusion. Post-thrombectomy, she was found to have a left atrial thrombus and 10 days later was started on apixaban 5 mg twice daily. On the fourth day of apixaban therapy, she experienced an INR increase to 2.3, prompting initiation of a vitamin K challenge for nutritional deficiency. Despite initial improvement, her INR increased to 2.7 a week after apixaban was initiated, coinciding with a decline in mental status and an apixaban peak level of 435.6 ng/mL (reference range 91-321 ng/mL). A computed tomography (CT) scan of her head showed new intracranial hemorrhage in the area of her previous infarction, prompting apixaban reversal with andexanet alfa. Unfortunately, the patient expired. This case report highlights the importance and difficulty in performing therapeutic drug monitoring in patients receiving oral anti-factor Xa inhibitors, revealing a downside to administration of high-risk medications that do not have readily available monitoring.

A ratiometric electrochemical probe for the quantification of apixaban in unprocessed plasma samples using carbon aerogel/BFO modified glassy carbon electrodes

A novel electrochemical probe was established for the quantification of apixaban (APX) in unprocessed plasma samples. Efficiently oxidized graphene oxide aerogels (EEGO-AGs) and nano-sized Bi₂Fe₄O₉ (BFO) particles were electrodeposited on the surface of a glassy carbon electrode (GCE). In this work, a ratiometric electrochemical method was introduced for APX detection to enhance the specificity of the probe in plasma samples. The fabricated ratiometric probe was employed for the indirect detection determination of APX using K₃[Fe(CN)₆]/K₄[Fe(CN)₆] as the redox pair. The differential pulse voltammetry technique was used to record the current alteration of the BFO/EEGO-AG-functionalized GCE probe at various APX concentrations. The probe response was proportional to the APX concentrations from 10 ng mL^-1 to 10 μg mL^-1 with a low limit of quantification (LLOQ) of 10 ng mL^-1. After validation, this method was successfully utilized for the determination of APX in patients' plasma samples who have taken APX regularly. The fabricated chemosensor detected APX concentrations in unprocessed plasma samples with high selectivity, resulting from the physical filtering antifouling activity of aerogels.

Risk factors associated with post-extraction bleeding in patients on warfarin or direct-acting oral anticoagulants: a retrospective cohort study

PURPOSE

The purpose of this study was to investigate the risk factors associated with post-extraction persistent bleeding in patients on warfarin or direct-acting oral anticoagulants (DOACs) and the ability of risk scores to predict post-extraction bleeding.

METHODS

Three hundred ninety-one patients taking warfarin or DOACs underwent tooth extractions. Various risk factors for post-extraction bleeding, including number of tooth extraction, with antiplatelet therapy, and risk scores, were investigated by univariate and multivariate analyses. A post-extraction bleeding was classified into grades 1-3.

RESULTS

The incidence of post-extraction bleeding was 26.8% (77 out of 287 patients; grade 1: 63, grade 2:14) in patients taking warfarin, and 26.0% (27 out of 104 patients; grade 1: 20, grade 2:7) in patients taking warfarin DOACs. Multivariate analyses showed that multiple teeth extractions and HAS-BLED scores (above 3 points) in patients taking warfarin, and only multiple teeth extractions in patients taking DOAC, were significantly associated with post-extraction bleeding, respectively.

CONCLUSION

Most of the post-extraction bleedings were grade 1, which can be stopped by eligibly pressing gauze by surgeons. If patients taking anticoagulants are scheduled to undergo multiple teeth extractions or their HAS-BLED score are above 3 points (if warfarin), we recommend informing patients risk of post-extraction bleeding before operation, taking carefully hemostasis, and instructing patients to bite down accurately on the gauze for longer than usual.

A synergy of liquid chromatography with high-resolution mass spectrometry and coagulation test for determination of direct oral anticoagulants for clinical and toxicological purposes

Direct oral anticoagulants are an alternative to anticoagulants based on vitamin K antagonists. Monitoring of direct oral anticoagulant concentration levels is necessary in specific cases (e.g. in emergency conditions, for determination of the cause of bleeding, adverse effects, risk of drug-direct oral anticoagulants interaction); therefore, a sensitive and specific method is needed. A methanol protein precipitation method followed by liquid chromatography with high-resolution mass spectrometry was developed for simultaneous separation and determination of apixaban, betrixaban, edoxaban, dabigatran, rivaroxaban and ximelagatran. The proposed method was fully validated in terms of linearity, the limits of detection and quantification, intra- and inter-day trueness and precision, recovery, matrix effect, process efficiency and stability. The method shows a strong correlation (Pearson's correlation coefficients > 0.92) with coagulation assays of apixaban, dabigatran and rivaroxaban (dilute thrombin time for gatrans and anti Xa factor (anti-Xa) activity for xabans). In addition, the developed method was applied for the identification and determination of apixaban and dabigatran in post-mortem serum samples. The developed method is a good alternative to coagulation tests which may show various interferences.

NOACs: an emerging class of oral anticoagulants-a review article

Background

NOACs, commonly known as novel oral anticoagulants, are the non-vitamin K antagonist oral anticoagulants which are relatively newer in the market. It has displaced vitamin K antagonists, notably warfarin, for many indications. These agents are dabigatran, rivaroxaban, apixaban, and edoxaban.

Main body

The drugs are licenced to prevent stroke and also systemic embolism in patients on treatment for atrial fibrillation and prevent venous thromboembolism. Rivaroxaban and apixaban are approved for prophylaxis of thrombus following surgical hip or knee arthroplasty. The recent surveys reveal that use of NOACs has steeply increased due to its safety profile and convenience to use. Also, the studies have shown that NOACs have lesser bleeding complications and associated mortality in contrast to traditional anticoagulants. The upcoming years are known to be NOACs’ age due to the significant findings in this area.

Conclusion

Therefore, a basic understanding on these drugs is highly recommended to provide a better service to the patients. This article aims to provide quick and brief information on the novel class of drugs. It equips an overview of NOAC and deals with the following areas: (i) pharmacology, (ii) laboratory methods, (iii) peri-operative management, (iv) advantages, (v) challenges, and (vi) future.

Dabigatran Monitoring Was Influenced by Thrombin Time Reagent With Different Thrombin Concentrations

To describe the effect of dabigatran on thrombin time (TT) reagents at different concentrations of thrombin. Pooled normal plasma enriched with dabigatran was dissolved in dimethylsulfoxide (DMSO) at concentrations of 0, 20, 50, 100, 200, 300, and 500 ng/mL. Samples with each concentration were evaluated using a semiautomatic coagulation analyzer to assess the effect of dabigatran on internal normalized ratio (INR), thromboplastin time (APTT), and TT, which were purchased from Instrument Laboratory (IL), Sysmex (SYS), and Stago (STA), respectively. Regarding INR, no reagent showed good sensitivity to increasing concentration of dabigatran, despite all reagents showing good linear response curves (P = .012). Regarding APTT, all reagents had low sensitivity to increasing dabigatran concentration, but SYS-APTT showed a better linear response curve (P = .001). Regarding TT, all reagents had a good linear response to the concentration of dabigatran; however, SYS-TT was very sensitive at low concentrations of dabigatran (0-100 ng/mL), while IL (TT-5 mL) and STA-TT were sensitive at medium concentrations of dabigatran (0-300 ng/mL), and IL (TT-2 mL) was less sensitive for a wide concentration of dabigatran (0-500 ng/mL; P = .007). Internal normalized ratio and APTT showed low sensitivity and SYS-TT showed high sensitivity to concentrations of dabigatran that were unsuitable to monitor. Both IL (TT-5 mL) and STA-TT were useful at medium concentrations of dabigatran by semiautomatic coagulation analyzer, which calculated results using the end point method of coagulation. Instrument Laboratory (TT-2 mL), which contains a higher concentration of thrombin, had better sensitivity to the concentration of dabigatran than APTT and was suitable for routine monitoring by an automatic analyzer.

Factor Xa Inhibitory Profile of Apixaban, Betrixaban, Edoxaban, and Rivaroxaban Does Not Fully Reflect Their Biologic Spectrum

The currently available oral anti-Xa agents are claimed to produce their anticoagulant and antithrombotic effects solely by the inhibition of factor Xa. This study profiled various anti-Xa drugs in routinely used laboratory assays to demonstrate that their effects are not solely related to the anti-Xa activities. Apixaban, betrixaban, edoxaban, and rivaroxaban were obtained commercially. Native and citrated whole blood was used for the activated clotting time (ACT) and thromboelastography (TEG). Citrated plasma was used for monitoring the prothrombin time (PT), activated partial thromboplastin time (aPTT), Heptest, and prothrombinase-induced clotting time (PiCT) tests. An amidolytic method was used for the determination of anti-Xa effects. Thrombin-induced fibrinokinetics was monitored optically. Thrombin generation studies were carried out using the calibrated automated thrombogram. All of the anti-Xa agents produced concentration- and assay-dependent effects. In the ACT at 2.5 μg/mL and TEG at 1.0 μg/mL, edoxaban exhibited the strongest anticoagulation effect. In the PiCT, PT, and aPTT assay at 1 μg/mL, edoxaban showed stronger effects than other agents. The half maximal inhibitory concentration of these agents for the inhibition of factor Xa ranged from 340 to >1000 ng/mL. In the thrombin generation inhibition assay, apixaban showed the strongest activity. In the fibrinokinetics, different anti-Xa agents produced varying degrees of inhibition. These results demonstrate that the measured anti-Xa activity alone does not fully reflect the overall biologic spectrum of these agents.

Transcriptomics and differential gene expression in Whitmania pigra (Annelida: Clitellata: Hirudinida: Hirudinidae): Contrasting feeding and fasting modes

The medicinal utility of leeches has been demonstrated through decades of use in modern hospital settings, mainly as relievers of venous congestion following flap or digit replantation surgery. In the present study, we sequence and annotate (through BLAST- and Gene Ontology-based approaches) the salivary transcriptome of the nonblood feeding hirudinid Whitmania pigra and assess the differential gene expression of anticoagulation factors (through both quantitative real-time PCR [qRT-PCR] and in silico-based methods) during feeding and fasting conditions. This was done in order to evince the diversity of putative anticoagulation factors, as well as estimate the levels of upregulation of genes immediately after feeding. In total, we found sequences with demonstrated orthology (via both phylogenetic analyses and BLAST-based approaches) to seven different proteins that have previously been linked to anticoagulatory capabilities-eglin C, bdellin, granulin, guamerin, hyaluronidase, destabilase I, and lipocalin. All of these were recovered from leeches both in the fasting and in the feeding conditions, but all show signs of upregulation in the feeding leeches. Interestingly, our RNA-seq effort, coupled with a hypergeometric test, indicated that the differentially expressed genes were disproportionately involved in three main immunological pathways (endocytosis, peroxisome regulation, and lysosome regulation). The results and implications of the finding of anticoagulants in this nonblood feeding leech and the putative upregulation of anticoagulation factors after feeding are briefly discussed in an evolutionary context.

Microfluidic coagulation assay for monitoring anticoagulant therapy in acute stroke patients

Reliable detection of anticoagulation status in patients treated with non-vitamin K antagonist oral anticoagulants (NOACs) is challenging but of importance especially in the emergency setting. This study evaluated the potential of a whole-blood clotting time assay based on Surface Acoustic Waves (SAW-CT) in stroke-patients. The SAW-technology was used for quick and homogenous recalcification of whole blood inducing a surface-activated clotting reaction quantified and visualised by real-time fluorescence microscopy with automatic imaging processing. In 20 stroke or transient ischaemic attack (TIA)-patients taking NOACs kinetics of SAW-CT were assessed and correlated to other coagulation parameters (PT, aPTT) and NOAC-plasma concentration measured by tandem mass spectrometry (LC-MS/MS). In 225 emergency patients with suspicion of acute stroke or TIA, SAW-CT values were assessed. Mean (± SD) SAW-CT in non-anticoagulated stroke patients (n=180) was 124 s (± 21). In patients on dabigatran or rivaroxaban, SAW-CT values were significantly higher 2 and 8 hours (h) after intake rising up to 267 seconds (s) (dabigatran, 2 h after intake) and 250 s (rivaroxaban, 8 h after intake). In patients on apixaban, SAW-CT values were only moderately increased 2 h after intake (SAW-CT 153 s). In emergency patients, SAW-CT values were significantly higher in NOAC and vitamin K antagonist (VKA)-treated as compared to non-anticoagulated patients. In conclusion, the SAW-CT assay is capable to monitor anticoagulant level and effect in patients receiving dabigatran, rivaroxaban and the VKA phenprocoumon. It has a limited sensitivity for apixaban-detection. If specific SAW-CT results were used as cut-offs, SAW-CT yields high diagnostic accuracy to exclude relevant rivaroxaban and dabigatran concentrations in stroke-patients.

Current knowledge on assessing the effects of and managing bleeding and urgent procedures with direct oral anticoagulants

PURPOSE

Current knowledge on managing major bleeding events with available hemostatic agents, including their combined use with potential reversal agents, in patients taking direct oral anticoagulant (DOACs) is reviewed.

SUMMARY

Over the past five years, a new generation of oral agents, the DOACs, has emerged as commonly used anticoagulants for stroke prevention in non-valvular atrial fibrillation, and treatment or secondary prevention of venous thromboembolism. Management of a bleeding event in the setting of DOAC therapy should take into account the relative risks of bleeding and thrombosis, which will determine the degree of anticoagulant reversal required. In the setting of a major (critical) bleeding event associated with notable blood loss, management may include transfusions of blood products to sustain the function of organ systems, and the availability of specific reversal agents will provide additional options for bleeding management. Beyond withholding the DOAC and providing supportive management that addresses any factors contributing to the bleeding event, clinicians may desire to expedite the removal of any anticoagulation effects. In general, this is accomplished by either removing or neutralizing the anticoagulant or by independently establishing hemostasis.

CONCLUSION

With or without reversal agents, patients may require supportive management such as mechanical pressure, volume support, transfusions of blood products, and, depending on the situation, surgery to repair the bleeding source. Specific reversal agents are currently under development or have recently been approved for the urgent management of bleeding events or the facilitation of invasive procedures in patients receiving DOACs.

Management of neurologic complications of coagulopathies

Coagulopathy is common in intensive care units (ICUs). Many physiologic derangements lead to dysfunctional hemostasis; these may be either congenital or acquired. The most devastating outcome of coagulopathy in the critically ill is major bleeding, defined by transfusion requirement, hemodynamic instability, or intracranial hemorrhage. ICU coagulopathy often poses complex management dilemmas, as bleeding risk must be tempered with thrombotic potential. Coagulopathy associated with intracranial hemorrhage bears directly on prognosis and outcome. There is a paucity of high-quality evidence for the management of coagulopathies in neurocritical care; however, data derived from studies of patients with intraparenchymal hemorrhage may inform treatment decisions. Coagulopathy is often broadly defined as any derangement of hemostasis resulting in either excessive bleeding or clotting, although most typically it is defined as impaired clot formation. Abnormalities in coagulation testing without overt clinical bleeding may also be considered evidence of coagulopathy. This chapter will focus on acquired conditions, such as organ failure, pharmacologic therapies, and platelet dysfunction that are associated with defective clot formation and result in, or exacerbate, intracranial hemorrhage, specifically spontaneous intraparenchymal hemorrhage and traumatic brain injury.

Perioperative Management of Anticoagulation-Review of Latest Evidence

Periprocedural anticoagulation bridging is recommended to reduce the risk of thromboembolic events in patients at a higher risk of developing thromboembolism during the perioperative period. The optimal periprocedural anticoagulation strategy has not been established. Unfractionated heparin and low molecular heparin are used in preventing thromboembolism in the special population. Novel oral anticoagulants that directly inhibit thrombin (dabigatran) or factor Xa (rivaroxaban, apixaban) are shown as effective anticoagulants in preventing thromboembolism (venous thromboembolism) in various medical conditions. They have the advantage of having a faster onset, shorter half-lives, easier monitoring, and predicable doses. But there are disadvantages to newer anticoagulants such as the unavailability of definitive reversal agents and lack of data in patients with renal insufficiency. We review the latest evidence on the effects of newer oral anticoagulants in preventing thromboembolism and its bleeding risks.

Factor Eight Inhibitor Bypassing Agent (FEIBA) for Reversal of Target-Specific Oral Anticoagulants in Life-Threatening Intracranial Bleeding

INTRODUCTION

As increasing number of patients present to emergency departments with life threatening hemorrhages, particularly intracranial hemorrhage on anticoagulation physicians must be cognizant of the limitations of the available reversal options. Based upon the available literature, our institution formulated a reversal algorithm for patients with life-threatening bleeding on factor Xa inhibitors by administering factor eight inhibitor bypassing agent (FEIBA) 20 units/kg.

METHODS

A retrospective chart review was performed to include all patients who received FEIBA per institutional protocol. This case series excluded patients who received FEIBA for reversal of dabigatran. Pre and post FEIBA CT scans were compared for changes. Finally, patients were stratified by estimated mortality rates calculated based on pre-intervention characteristics via published risk models.

RESULTS

Thirteen patients were initially included in this study yet two patients were excluded because they were on dabigatran. Fifty-five percent of patients demonstrated stable ICH on CT scan after FEIBA administration while thirty-six percent showed worsening scans. Two patients developed thrombotic events after FEIBA administration.

DISCUSSION

FEIBA is a treatment option in patients on a TSOA with acute intracranial hemorrhage with evidence of at least partial pharmacologic reversal of their anticoagulation status. There does not appear to be any major risk of thromboembolic complications associated with FEIBA. Much larger study sizes will be necessary to establish statically significant clinical efficacy for FEIBA use in this patient population. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Emergency medicine physicians are first-line caretakers for patients with life threatening intracranial hemorrhages whether spontaneous or traumatic. FEIBA is a potentially safe option to reverse TSOA in this patient population.

Anticoagulation Therapy Considerations in Factor VII Deficiency

Factor VII (FVII) deficiency is the most prevalent rare bleeding disorder in the USA and affects approximately 1 out of every 500,000 people. Warfarin inhibits the synthesis of FVII, in addition to other clotting factors. Warfarin is contraindicated in patients with bleeding tendencies or blood dyscrasias; therefore, the literature regarding the use of warfarin in FVII deficiency is very limited. We report a successful re-challenge of warfarin therapy in a patient with FVII deficiency. A 70-year-old woman with FVII deficiency experienced a significant decrease in FVII activity and subsequent vaginal bleeding roughly 5 weeks after starting warfarin for atrial fibrillation. The patient was switched to aspirin therapy. Nearly 4 years later, warfarin therapy was re-attempted by a different haematologist. After 9 months, FVII activity remained in an acceptable range and no bleeding events had occurred. In addition, once the maintenance dose was established, the international normalized ratio remained within the goal range (1.5-2.0) for the majority of assessments. Regarding future considerations, we hypothesize that anticoagulants that do not directly affect FVII, such as the direct oral anticoagulants, would carry less risk of bleeding complications and therefore may be safer alternatives to warfarin to reduce the risk of thromboembolic stroke in patients with atrial fibrillation and FVII deficiency.

Discontinuation and Management of Direct-Acting Anticoagulants for Emergency Procedures

Patients taking direct oral anticoagulants (DOACs) who then need an emergency invasive procedure require specialized management strategies. Appropriate patient evaluation includes assessment of the current anticoagulation state, including timing of the last dose. DOACs require particular coagulation assays to measure anticoagulation levels accurately, although standard coagulation screening tests may provide qualitative guidance. Specialty societies have endorsed general recommendations for patient management to promote hemostasis in anticoagulated patients requiring surgery or other invasive procedures. These include general stopping rules (such as ≥24 hours for low-risk procedures and ≥48 hours for high-risk surgery with normal renal function) for elective procedures. Bridging therapy when oral anticoagulant treatment is interrupted has recently been questioned, depending on the clinical scenario. Novel agents for the reversal of DOAC-induced anticoagulation have recently been developed. Idarucizumab, a humanized monoclonal antibody fragment that selectively binds dabigatran, was recently approved for clinical use in patients with life-threatening or uncontrolled bleeding, and for patients requiring emergency interventions. Idarucizumab can streamline the pre- and periprocedural anticoagulation management of dabigatran-treated patients, as it provides fast, complete, and sustainable reversibility. Andexanet alfa is an inactive, decoy factor Xa (FXa) molecule that binds FXa inhibitors, and ciraparantag is a synthetic molecule designed to bind fractionated and unfractionated heparins, and each of the currently approved DOACs. As clinical development of the additional anti-FXa-specific anticoagulant reversal agents proceeds, the respective role of each in the management of emergency bleeding events and invasive procedures will be better defined, and it is hoped they will make important contributions to patient care.

Reversal Strategies for NOACs: State of Development, Possible Clinical Applications and Future Perspectives

The non-vitamin K antagonist oral anticoagulants (NOACs) are used for thromboembolic prophylaxis of patients with atrial fibrillation and in the treatment as well as secondary prophylaxis of patients with venous thromboembolism. Even though NOACs have a better safety profile than vitamin K antagonists (VKAs), there will still be bleeding complications on NOAC treatment. In some cases, stopping the NOAC and non-drug-related management such as manual compression and interventional endoscopy will be sufficient to stop the bleeding. In more serious bleeding events and before acute surgery, coagulation factor concentrates or NOAC-specific antidotes could be used. Coagulation factor concentrates can be used in patients with haemophilia and to reverse the effect of VKAs but, in NOAC-treated patients, results are inconsistent and these agents could potentially have pro-thrombotic effects. Specific antidotes for NOACs are expected to be on the market soon. Phase III clinical trials with a humanized antibody fragment directed against dabigatran (idarucizumab) and recombinant, modified factor Xa (andexanet alfa) are ongoing. A molecule (aripazine) with broad activity against various anticoagulants including NOACs is currently undergoing phase II trials. For use of these specific antidotes, it is desirable that measurements for coagulation activity with a short response delay are widely available for the different NOACs and further research in this field is needed. Furthermore, guidelines for antidote use, including general measures for the treatment of NOAC-related bleeding, should be available.

Anti-Xa bioassays for the laboratory measurement of direct Factor Xa inhibitors in plasma, in selected patients

In the past decade Direct Oral Anti-Coagulants (DOACs), targeting Thrombin or Factor Xa, have enormously facilitated the daily treatment of all relevant patients, including those requiring lifelong therapy. These DOACs have considerable advantages over the use of oral Vitamin K Antagonist (VKA) treatments, in view of having little interferences with food and other medications and also not requiring adjustment for age, gender or weight, with some well-defined exceptions. In this current What's Happening Section we focus on measurements of DiXaIs in plasma using anti-Xa assays, with the objective of providing a tribute to Professor Michel Meyer Samama, who was not only a real leader in this field but, in the past, both authors benefited from his wisdom, as a teacher who dedicated his scientific and professional life (among many other interests in hemostasis, thrombosis and fibrinolysis) to develop and promote methods and strategies for laboratory monitoring of anticoagulants. This review presents the performance characteristics of the Anti-Factor Xa assays (measuring Factor Xa inhibition by drugs), which are available for measuring Direct Factor Xa Inhibitors in plasma, and show good compliance of the results with the reference LC:MS method (which measures the mass of Direct Factor Xa Inhibitors). We also present the preparation and validation of drug specific plasma calibrators and controls which are requested for drug measurements. These assays are convenient and practical laboratory tools which can be used in any laboratory setting, and meet the requirements of regulatory bodies for making smart, quantitative, sensitive, accurate and ease of use assays for measuring DOACs when needed. The manuscript focuses mainly on the following areas of current interest: interference in coagulation assays; anti-Xa laboratory methods; development of calibrators and controls for DiXaIs; method validation and comparison with reference techniques (LC:MS); regulatory requirements and method registrations; newer clinical applications and experience on DiXaIs with Anti-Xa assays, and future perspectives.

Erratum to: Pharmacology of anticoagulants used in the treatment of venous thromboembolism

Anticoagulant drugs are the foundation of therapy for patients with VTE. While effective therapeutic agents, anticoagulants can also result in hemorrhage and other side effects. Thus, anticoagulant therapy selection should be guided by the risks, benefits and pharmacologic characteristics of each agent for each patient. Safe use of anticoagulants requires not only an in-depth knowledge of their pharmacologic properties but also a comprehensive approach to patient management and education. This paper will summarize the key pharmacologic properties of the anticoagulant agents used in the treatment of patients with VTE.

A rapid pro-hemostatic approach to overcome direct oral anticoagulants

Direct inhibitors of coagulation factor Xa (FXa) or thrombin are promising oral anticoagulants that are becoming widely adopted. The ability to reverse their anticoagulant effects is important when serious bleeding occurs or urgent medical procedures are needed. Here, using experimental mouse models of hemostasis, we show that a variant coagulation factor, FXa(I16L), rapidly restores hemostasis in the presence of the anticoagulant effects of these inhibitors. The ability of FXa(I16L) to reverse the anticoagulant effects of FXa inhibitor depends, at least in part, on the ability of the active site inhibitor to hinder antithrombin-dependent FXa inactivation, paradoxically allowing uninhibited FXa to persist in plasma. Because of its inherent catalytic activity, FXa(I16L) is more potent (by >50-fold) in the hemostasis models tested than a noncatalytic antidote that is currently in clinical development. FXa(I16L) also reduces the anticoagulant-associated bleeding in vivo that is induced by the thrombin inhibitor dabigatran. FXa(I16L) may be able to fill an important unmet clinical need for a rapid, pro-hemostatic agent to reverse the effects of several new anticoagulants.

Evaluation of the chromogenic anti-factor IIa assay to assess dabigatran exposure in geriatric patients with atrial fibrillation in an outpatient setting

Background

Dabigatran etexilate may be underutilized in geriatric patients because of inadequate clinical experience in individuals with severe renal impairment and post-marketing reports of bleeding events. Assessing the degree of anticoagulation may improve the risk:benefit ratio for dabigatran. The aim of this prospective study was to identify whether therapeutic drug monitoring of dabigatran anticoagulant activity using a chromogenic anti-factor IIa assay is a viable option for therapy individualization.

Methods

Plasma dabigatran concentration was assessed in nine patients with nonvalvular atrial fibrillation aged 75 years or older currently receiving dabigatran etexilate for prevention of stroke, using an anti-factor IIa chromogenic assay and HPLC-MS/MS. Trough concentrations were evaluated on two separate occasions to determine intrapatient variation.

Results

Blood was collected at 13.1 ± 2.3 h (mean ± SD) post dose from patients prescribed dabigatran etexilate 150 mg twice daily (5/9 patients) or dabigatran etexilate 75 mg twice daily (4/9 patients). Results from the anti-factor IIa chromogenic assay correlated with dabigatran concentrations as assessed by HPLC-MS/MS (r² = 0.81, n = 16). There was no correlation between dabigatran trough values taken at separate visits (r² = 0.002, n = 7). Furthermore, there was no correlation found between the drug concentrations and patients’ renal function determined by both creatinine and cystatin-C based equations. None of the patients enrolled in the study were in the proposed on-therapy trough range during at least one visit.

Conclusion

The chromogenic anti-factor IIa assay demonstrated similar performance in quantifying dabigatran plasma trough concentrations to HPLC-MS/MS. Single measurement of dabigatran concentration by either of two methods during routine visits may not be reliable in identifying patients at consistently low or high dabigatran concentrations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12959-016-0084-2) contains supplementary material, which is available to authorized users.

Pharmacology of anticoagulants used in the treatment of venous thromboembolism

Anticoagulant drugs are the foundation of therapy for patients with VTE. While effective therapeutic agents, anticoagulants can also result in hemorrhage and other side effects. Thus, anticoagulant therapy selection should be guided by the risks, benefits and pharmacologic characteristics of each agent for each patient. Safe use of anticoagulants requires not only an in-depth knowledge of their pharmacologic properties but also a comprehensive approach to patient management and education. This paper will summarize the key pharmacologic properties of the anticoagulant agents used in the treatment of patients with VTE.

Monitoring of hematological and hemostatic parameters in neurocritical care patients

Anemia and bleeding are paramount concerns in neurocritical care and often relate to the severity of intracranial hemorrhage. Anemia is generally associated with worse outcomes, and efforts to minimize anemia through reduced volume of blood sampled are encouraged. Point-of-care-testing reliably detects the use of non-steroidal anti-inflammatory drugs that may worsen bleeding and reduce platelet activity, particularly in patients with intracerebral hemorrhage. How best to monitor the effect of platelet transfusion or platelet-activating therapy is not well studied. For patients known to take novel oral anticoagulants, drug-specific coagulation tests before neurosurgical intervention are prudent.

Direct oral anticoagulants: new drugs and new concepts

Direct oral anticoagulants (DOACs) are approved for multiple thromboembolic disorders and provide advantages over existing agents. As with all anticoagulants, management protocols for the eventuality of bleeding are important. Randomized phase III studies generally show that DOACs have a similar risk of clinically relevant bleeding compared with standard anticoagulants, with reductions in major bleeding in some cases. This may be particularly important in patients with atrial fibrillation, for whom the rate of intracranial hemorrhage was approximately halved with DOACs compared with warfarin. Conversely, the risk of gastrointestinal bleeding may be increased. Specific patient characteristics, such as renal impairment, comedications, and particular aspects of each drug, including the proportion eliminated by the kidneys, must be taken into account when assessing the risk of bleeding. Although routine coagulation monitoring of DOACs is not required, it may be useful under some circumstances. Of the traditional clotting assays, a sensitive and calibrated prothrombin time may be useful for detecting the presence or absence of clinically relevant factor Xa inhibitor concentrations (rivaroxaban or apixaban), but specific anti-factor Xa assays can measure drug levels quantitatively. For dabigatran, the results of an activated partial thromboplastin time test may exclude a clinically relevant pharmacodynamic effect, but a calibrated dilute thrombin time assay can be used for quantification of drug levels. In the event of mild or moderate bleeding, normal hemostatic support measures are recommended. For life-threatening bleeding, use of nonspecific prohemostatic agents may be considered, although clinical evidence is scarce. Specific antidotes are in development.

New Oral Anticoagulants: How Do We Use Them Wisely?

The relative efficacy and safety of new oral anticoagulants (NOAC) have been consistent across a wide range of patients in clinical trials. On the one hand, they have offered new therapeutic options for stroke prevention in patients with atrial fibrillation (AF) and patients do like the experience of no need of frequent blood draws. On the other hand, their expensive prices, different formulary plans from different insurance companies, lack of antidote, and no method of monitoring the therapy are some of the challenges on their use in clinical practice. This narrative review aims to help clinicians understand these new oral anticoagulants better and choose them wisely according to their indications. In addition, other issues related to the use of NOAC, such as cost and methods of reversing their effects in hemorrhagic conditions, are also discussed.

Monitoring the Effects and Antidotes of the Non-vitamin K Oral Anticoagulants

In the last decade, we have witnessed the emergence of the oral non-vitamin K oral anticoagulants (NOACs), which have numerous advantages compared with the vitamin K antagonists, particularly their lack of need for monitoring; as a result their use is increasing. Nonetheless, the NOACs face two major challenges: the need for reliable laboratory assays to assess their anticoagulation effect, and the lack of approved antidotes to reverse their action. This article provides an overview of monitoring the anticoagulant effect of NOACs and their potential specific antidotes in development.

Facile chemoenzymatic synthesis of biotinylated heparosan hexasaccharide

A biotinylated heparosan hexasaccharide was synthesized using a one-pot multi-enzyme strategy, in situ activation and transfer of N-trifluoroacetylglucosamine (GlcNTFA) to a heparin backbone significantly improved the synthetic efficiency. The biotinylated hexasaccharide could serve as a flexible core to diversify its conversion into heparan sulfate isoforms with potential biological applications and therapeutics.

Determination of dabigatran, rivaroxaban and apixaban by ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) and coagulation assays for therapy monitoring of novel direct oral anticoagulants

BACKGROUND

Three novel direct oral anticoagulants (DOACs) have recently been registered by the Food and Drug Administration and European Medicines Agency Commission: dabigatran, rivaroxaban, and apixaban. To quantify DOACs in plasma, various dedicated coagulation assays have been developed.

OBJECTIVE

To develop and validate a reference ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) method and to evaluate the analytical performance of several coagulation assays for quantification of dabigatran, rivaroxaban, and apixaban.

METHODS

The developed UPLC-MS/MS method was validated by determination of precision, accuracy, specificity, matrix effects, lower limits of detection, carry-over, recovery, stability, and robustness. The following coagulation assays were evaluated for accuracy and precision: laboratory-developed (LD) diluted thrombin time (dTT), Hemoclot dTT, Pefakit PiCT, ECA, Liquid anti-Xa, Biophen Heparin (LRT), and Biophen DiXal anti-Xa. Agreement between the various coagulation assays and UPLC-MS/MS was determined with random samples from patients using dabigatran or rivaroxaban.

RESULTS

The UPLC-MS/MS method was shown to be accurate, precise, sensitive, stable, and robust. The dabigatran coagulation assay showing the best precision, accuracy and agreement with the UPLC-MS/MS method was the LD dTT test. For rivaroxaban, the anti-factor Xa assays were superior to the PiCT-Xa assay with regard to precision, accuracy, and agreement with the reference method. For apixaban, the Liquid anti-Xa assay was superior to the PiCT-Xa assay.

CONCLUSIONS

Statistically significant differences were observed between the various coagulation assays as compared with the UPLC-MS/MS reference method. It is currently unknown whether these differences are clinically relevant. When DOACs are quantified with coagulation assays, comparison with a reference method as part of proficiency testing is therefore pivotal.

Direct oral anticoagulants as alternative treatment options for the effective long-term treatment of patients with pulmonary embolism in primary care: a review

Pulmonary embolism (PE) represents a potentially life-threatening venous thromboembolic disorder, and prompt treatment is vital to prevent early mortality. However, diagnosis of PE is complicated by the range of signs and symptoms with which it presents. Clinical risk scores, imaging techniques, and laboratory tests are recommended in clinical guidelines to aid diagnosis, and risk stratification strategies can be used to inform treatment decisions. Long-term anticoagulation is key to avoid the risk of later complications of acute PE, such as recurrent venous thromboembolism and chronic thromboembolic pulmonary hypertension. Rivaroxaban is a direct oral anticoagulant that has been approved for the treatment of PE (and deep vein thrombosis) and prevention of recurrent venous thromboembolism; other direct oral anticoagulants have undergone phase III trials for these indications. These agents may provide advantages over traditional anticoagulants, such as vitamin K antagonists, because they are administered at fixed doses and do not require routine coagulation monitoring. These advantages may improve patient adherence and aid general practitioners by simplifying long-term management of PE in daily primary care.

Pharmacology and laboratory testing of the oral Xa inhibitors

New oral factor Xa inhibitors are intended to progressively substitute the oral vitamin K antagonists and parenteral indirect inhibitors of factor Xa in the prevention and treatment of venous and arterial thromboembolic episodes. This article focuses on the main clinical studies and on biological measurements of new oral factor Xa inhibitors, and addresses several safety issues. These newer agents do not require any routine laboratory monitoring of blood coagulation; however, biological tests have been developed in order to assess the plasma concentration of these drugs in several clinical settings. This article reviews these 4 oral direct factor Xa inhibitors.

New oral anticoagulants in patients with nonvalvular atrial fibrillation: a review of pharmacokinetics, safety, efficacy, quality of life, and cost effectiveness

Atrial fibrillation (AF) continues to be a leading cause of cerebrovascular morbidity and mortality resulting from cardioembolic stroke. Oral anticoagulation therapy has been shown to decrease the incidence of cardioembolic stroke in patients with AF by more than 50%. Appropriate use of anticoagulation with vitamin K antagonists requires precise adherence and monitoring. A number of factors that potentially induce patients’ dissatisfaction reduce quality of patient life. New direct oral anticoagulants, such as the direct factor Xa inhibitors rivaroxaban, apixaban, edoxaban, and the thrombin inhibitor dabigatran, were developed to overcome the limitations of the conventional anticoagulant drugs. However, models to optimize the benefit of therapy and to ensure that therapy can be safely continued are missing for the new oral anticoagulants. This review will briefly describe the new oral anticoagulants dabigatran, rivaroxaban, apixaban, and edoxaban with focus on their use for prevention of embolic events in AF. Moreover, it will discuss the safety, efficacy, cost data, and benefit for patients’ quality of life and adherence.