Antithrombotic and prohemorrhagic actions of different concentrations of apixaban in patients exposed to single and dual antiplatelet regimens

We evaluated modifications in the hemostatic balance of different concentrations of apixaban (APIX) in 25 healthy donors and 53 patients treated with aspirin (ASA, n = 21), ASA and clopidogrel (ASA + CLOPI, n = 11), or ASA and ticagrelor (ASA + TICA, n = 21). Blood samples from participants were spiked ex vivo with apixaban 0 (APIX0), 40 (APIX40), and 160 ng/mL (APIX160). We assessed the effects of APIX on (1) clot formation, by ROTEM thromboelastometry; (2) thrombin generation primed by platelets; and (3) platelet and fibrin interactions with a thrombogenic surface, in a microfluidic model with circulating blood. APIX caused dose-related prolongations of clotting time with minimal impact on other ROTEM parameters. Thrombin generation was significantly inhibited by APIX160, with ASA + TICA actions showing the strongest inhibition (p < 0.01 vs APIX0). Microfluidic studies showed that APIX160 was more potent at suppressing platelet and fibrin interactions (p < 0.001 vs. APIX0). APIX40 demonstrated a consistent antithrombotic action but with a favorable protective effect on the structural quality of fibrin. APIX potentiated the antithrombotic effects of current antiplatelet regimens. APIX at 40 ng/mL, enhanced the antithrombotic action of single or dual antiplatelet regimens but was more conservative for hemostasis than the 160 ng/mL concentration.

Clinical Relevance of Preclinical and Clinical Studies of Four-Factor Prothrombin Complex Concentrate for Treatment of Bleeding Related to Direct Oral Anticoagulants

Direct oral anticoagulants (DOACs) are widely used for the prevention and treatment of venous thromboembolism and stroke. When emergency reversal of DOAC-related anticoagulation is required, specific DOAC reversal agents are recommended, including idarucizumab for dabigatran reversal and andexanet alfa for apixaban and rivaroxaban reversal. However, specific reversal agents are not always available, andexanet alfa has not been approved for urgent surgery, and clinicians need to know the patient's anticoagulant medication before administering these treatments. Four-factor prothrombin complex concentrates (4F-PCCs) are recognized as nonspecific, alternative hemostatic agents for treatment of DOAC-related bleeding. Evidence from preclinical and clinical studies shows that they may reduce the anticoagulant effects of DOACs and may help control DOAC-related bleeding. However, randomized controlled trials are lacking, and most data are from retrospective or single-arm prospective studies in bleeding associated with activated factor X inhibitors. There are no clinical data showing the efficacy of 4F-PCC for the treatment of bleeding in dabigatran-treated patients. This review focuses on the current evidence of 4F-PCC use in controlling bleeding associated with DOACs and provides an expert opinion on the relevance of these data for clinical practice. The current treatment landscape, unmet needs, and future directions are also discussed.

DOAC-associated bleeding, hemostatic strategies, and thrombin generation assays - a review of the literature

Direct oral anticoagulants (DOACs) account for most oral anticoagulant use. DOAC-associated bleeding events are commonly encountered in clinical practice and are associated with substantial morbidity and mortality. Both specific reversal agents and nonspecific hemostatic therapies, such as prothrombin complex concentrates, are used in the management of DOAC-associated bleeding. Measuring hemostatic efficacy and demonstrating a clinical impact from these therapies among studies of bleeding patients is challenging. Thrombin generation assays provide information on the total hemostatic potential of plasma, and have emerged as a promising modality to both measure the impact of DOACs on coagulation and to evaluate the effects of hemostatic therapies among patients with DOAC-associated bleeding. The mechanisms by which nonspecific hemostatic agents impact coagulation and thrombin generation in the context of DOAC therapy are unclear. As a result, we undertook a review of the literature using a systematic search strategy with the goal of summarizing the effects of DOACs on thrombin generation and the effects of both specific reversal agents and nonspecific hemostatic therapies on DOAC-altered thrombin generation parameters. We sought to identify clinical studies focusing on whether altered thrombin generation is associated with clinical bleeding and whether correction of altered thrombin generation parameters predicts improvements in clinical hemostasis. Lastly, we sought to outline future directions for the application of thrombin generation assays toward anticoagulation therapies and the question of anticoagulation reversal.

Reversing Rivaroxaban Anticoagulation as Part of a Multimodal Hemostatic Intervention in a Polytrauma Animal Model

BACKGROUND

Life-threatening bleeding requires prompt reversal of the anticoagulant effects of factor Xa inhibitors. This study investigated the effectiveness of four-factor prothrombin complex concentrate in treating trauma-related hemorrhage with rivaroxaban-anticoagulation in a pig polytrauma model. This study also tested the hypothesis that the combined use of a low dose of prothrombin complex concentrate plus tranexamic acid and fibrinogen concentrate could improve its subtherapeutic effects.

METHODS

Trauma (blunt liver injury and bilateral femur fractures) was induced in 48 anesthetized male pigs after 30 min of rivaroxaban infusion (1 mg/kg). Animals in the first part of the study received prothrombin complex concentrate (12.5, 25, and 50 U/kg). In the second part, animals were treated with 12.5 U/kg prothrombin complex concentrate plus tranexamic acid or plus tranexamic acid and fibrinogen concentrate. The primary endpoint was total blood loss postinjury. The secondary endpoints (panel of coagulation parameters and thrombin generation) were monitored for 240 min posttrauma or until death.

RESULTS

The first part of the study showed that blood loss was significantly lower in the 25 U/kg prothrombin complex concentrate (1,541 ± 269 ml) and 50 U/kg prothrombin complex concentrate (1,464 ± 108 ml) compared with control (3,313 ± 634 ml), and 12.5 U/kg prothrombin complex concentrate (2,671 ± 334 ml, all P < 0.0001). In the second part of the study, blood loss was significantly less in the 12.5 U/kg prothrombin complex concentrate plus tranexamic acid and fibrinogen concentrate (1,836 ± 556 ml, P < 0.001) compared with 12.5 U/kg prothrombin complex concentrate plus tranexamic acid (2,910 ± 856 ml), and there were no early deaths in the 25 U/kg prothrombin complex concentrate, 50 U/kg prothrombin complex concentrate, and 12.5 U/kg prothrombin complex concentrate plus tranexamic acid and fibrinogen concentrate groups. Histopathologic analyses postmortem showed no adverse events.

CONCLUSIONS

Prothrombin complex concentrate effectively reduced blood loss, restored hemostasis, and balanced thrombin generation. A multimodal hemostatic approach using tranexamic acid plus fibrinogen concentrate enhanced the effect of low doses of prothrombin complex concentrate, potentially reducing the prothrombin complex concentrate doses required for effective bleeding control.

EDITOR’S PERSPECTIVE

ROTEM Testing for Direct Oral Anticoagulants

Direct oral anticoagulants (DOACs) are increasingly used worldwide for the prevention of stroke in patients with atrial fibrillation and to prevent or treat venous thromboembolism. In situations such as serious bleeding, the need for urgent surgery/intervention or the management of a thromboembolic event, the laboratory measurement of DOACs levels or anticoagulant activity may be required. Rotational thromboelastometry (ROTEM) is a viscoelastic hemostatic assay (VHA) which has been used in emergencies (trauma and obstetrics), and surgical procedures (cardiac surgery and liver transplants), but experience with this assay in DOACs-treated patients is still limited. This article reviews the use of ROTEM in the setting of DOACs therapy, focusing on DOACs-associated bleeding and the use of this VHA for the management of reversal strategies for DOACs-associated anticoagulation.

Effects of electret coating technology on coronary stent thrombogenicity

Stent thrombosis (ST) is a catastrophic event and efforts to reduce its incidence by altering blood-stent interactions are longstanding. A new electret coating technology that produces long-lasting negative charge on stent surface could make them intrinsically resistant to thrombosis. We assessed the thrombogenicity of stents using an annular perfusion model with confocal microscopy, and determined the efficacy of electret coating technology to confer thrombo-resistant properties to standard stents. Using an annular perfusion chamber, Bare Metal Stent (BMS), standard uncoated DES (DES), and Electret-coated DES (e-DES) were exposed to human blood under arterial flow conditions. Deposits of fibrinogen and platelets on the stent surface were analyzed using immunofluorescence staining and confocal microscopy. Surface coverage by fibrinogen and platelets and the deposit/aggregate size were quantified using computerized morphometric analysis. The experimental methodology produced consistent, quantifiable results. Area of stent surface covered by fibrinogen and platelets and the average size of the deposits/aggregates were lowest for e-DES and highest on BMS, with DES in the middle. The size of fibrinogen-deposits showed no differences between the stents. The testing methodology used in our study successfully demonstrated that electret coating confers significant antithrombotic property to DES stents. These findings warrant confirmation in a larger study.

Andexanet versus prothrombin complex concentrates: Differences in reversal of factor Xa inhibitors in in vitro thrombin generation

BACKGROUND

Andexanet alfa (andexanet) is a modified human factor Xa (FXa) approved for anticoagulation reversal in patients with life-threatening bleeding treated with rivaroxaban or apixaban. Four-factor prothrombin complex concentrates (4F-PCCs) are approved for reversal of vitamin K antagonist-induced anticoagulation but not FXa inhibitors. The mechanism and effectiveness of 4F-PCCs for FXa inhibitor reversal are unclear.

OBJECTIVE

To investigate the mechanism and impact of 4F-PCCs on reversal of rivaroxaban and apixaban in vitro compared to andexanet.

METHODS

The effect of 4F-PCCs (or individual factors) on tissue factor-initiated thrombin generation (TF-TG) was evaluated in human plasma, with or without rivaroxaban or apixaban, and compared with andexanet under the same conditions.

RESULTS

In the TF-TG assay, 4F-PCC completely reversed warfarin anticoagulation. Andexanet normalized TF-TG over a wide range of apixaban and rivaroxaban concentrations tested (19-2000 ng/mL). However, 4F-PCC (or individual factors) was unable to normalize endogenous thrombin potential (ETP) or peak thrombin (Peak) in the presence of apixaban or rivaroxaban (75-500 ng/mL). TF-TG was only normalized by 4F-PCC at inhibitor concentrations <75 ng/mL (ETP) or <37.5 ng/mL (Peak). These data can be explained by the estimated thresholds of FXa activity required to support normal TF-TG based on the inhibitor:FXa ratios and levels of uninhibited FXa. The data are consistent with healthy volunteer studies where TF-TG is not normalized until inhibitor levels are substantially decreased.

CONCLUSIONS

Both the theoretical calculations and experimental data demonstrated that 4F-PCCs are only able to normalize TG over a low and narrow range of FXa inhibitor concentrations (<75 ng/mL).

Sensitivity of Viscoelastic Tests to Platelet Function

Viscoelastic tests provide a dynamic assessment of coagulation, by exploring the time to clot formation and the clot strength. Using specific activators or inhibitors, additional factors can be explored, like the fibrinogen contribution to clot strength. Since the early days, various attempts have been done to measure platelet function with viscoelastic test. In general, the difference between the maximum clot strength and the fibrinogen contribution is considered an index of platelet contribution. However, this parameter does not clearly split platelet count from function; additionally, the extensive thrombin generation of standard activated viscoelastic tests activates platelet through the protease activated receptors, bypassing the other pathways. For this reason, standard viscoelastic tests cannot be used to assess platelet reactivity under the effects of aspirin or P2Y12 inhibitors. To overcome this limitation, a specific test was developed (thromboelastography platelet mapping). This test has been compared with the gold standard of light transmission aggregometry and with other point-of-care tests, with conflicting results. In general, the use of viscoelastic tests to assess the effects of antiplatelet agents is still limited. Conversely, platelet contribution to clot strength in the setting of coagulopathic bleeding is considered an important parameter to trigger platelet transfusion or desmopressin.

Four-factor Prothrombin Complex Concentrate for the Management of Patients Receiving Direct Oral Activated Factor X Inhibitors

Factor Xa inhibitors prevent thrombosis but are associated with severe or life-threatening bleeding. Here, the authors present data on four-factor prothrombin complex concentrates in management of anticoagulation-associated bleeding and restoring hemostasis, including recent results from the UPRATE study.

Idarucizumab, but not procoagulant concentrates, fully restores dabigatran-altered platelet and fibrin components of hemostasis

BACKGROUND

Comparative studies on the restoration of hemostasis with different reversal agents after dabigatran therapy have not been performed. We compared the efficacy and prothrombotic potential of the specific antidote idarucizumab with that of previously recommended non-specific procoagulant concentrates.

STUDY DESIGN AND METHODS

We explored the in vitro effects of dabigatran (184 ng/mL) on fibrin and platelet-aggregate formation onto a damaged vessel under flow conditions (600 s^-1 ). The reversal mechanisms and efficacy of idarucizumab (0.3-3 mg/mL) were compared with that of the non-specific procoagulant concentrates aPCC (25-75 U/Kg), PCC (70 U/Kg), or rFVIIa (120 μg/Kg). Generation of thrombin and prothrombin fragment (F1 + 2), and thromboelastometry parameters of clot formation were measured.

RESULTS

Dabigatran caused pronounced reductions in fibrin (87%) and platelet interactions (36%) with damaged vessels (p < 0.01) and significantly impaired thrombin generation and thromboelastometric parameters (delayed dynamics and reduced firmness). Idarucizumab completely normalized rates of fibrin and platelet coverage to baseline values in flow studies; and reversed the alterations in thrombin generation, F1 + 2 and thromboelastometry parameters produced by dabigatran. In comparison, aPCC and PCC only partially compensated for the dabigatran-induced alterations in fibrin deposition, but were unable to fully restore them to baseline values. Reversal with aPCC or PCC improved the majority of alterations in coagulation-related tests, but tended to overcompensate thrombin generation kinetics and significantly increased F1 + 2 levels.

CONCLUSION

Idarucizumab antagonizes alterations of direct and indirect biomarkers of hemostasis caused by dabigatran. In our studies, idarucizumab was clearly more efficacious than strategies with non-specific procoagulant concentrates and devoid of the excessive procoagulant tendency observed with the latter.

Association of prothrombin complex concentrate administration and hematoma enlargement in non-vitamin K antagonist oral anticoagulant-related intracerebral hemorrhage

OBJECTIVE

To investigate parameters associated with hematoma enlargement in non-vitamin K antagonist oral anticoagulant (NOAC)-related intracerebral hemorrhage (ICH).

METHODS

This retrospective cohort study includes individual patient data for 190 patients with NOAC-associated ICH over a 5-year period (2011-2015) at 19 departments of neurology across Germany. Primary outcome was the association of prothrombin complex concentrate (PCC) administration with hematoma enlargement. Subanalyses were calculated for blood pressure management and its association with the primary outcome. Secondary outcomes include associations with in-hospital mortality and functional outcome at 3 months assessed using the modified Rankin Scale.

RESULTS

The study population for analysis of primary and secondary outcomes consisted of 146 NOAC-ICH patients with available follow-up imaging. Hematoma enlargement occurred in 49/146 (33.6%) patients with NOAC-related ICH. Parameters associated with hematoma enlargement were blood pressure ≥ 160mmHg within 4 hours and-in the case of factor Xa inhibitor ICH-anti-Xa levels on admission. PCC administration prior to follow-up imaging was not significantly associated with a reduced rate of hematoma enlargement either in overall NOAC-related ICH or in patients with factor Xa inhibitor intake (NOAC: risk ratio [RR] = 1.150, 95% confidence interval [CI] = 0.632-2.090; factor Xa inhibitor: RR = 1.057, 95% CI = 0.565-1.977), regardless of PCC dosage given or time interval until imaging or treatment. Systolic blood pressure levels < 160mmHg within 4 hours after admission were significantly associated with a reduction in the proportion of patients with hematoma enlargement (RR = 0.598, 95% CI = 0.365-0.978). PCC administration had no effect on mortality and functional outcome either at discharge or at 3 months.

INTERPRETATION

In contrast to blood pressure control, PCC administration was not associated with a reduced rate of hematoma enlargement in NOAC-related ICH. Our findings support the need of further investigations exploring new hemostatic reversal strategies for patients with factor Xa inhibitor-related ICH. Ann Neurol 2018;83:186-196.

The impact of prothrombin complex concentrates when treating DOAC-associated bleeding: a review

Background

Bleeding complications are a risk associated with all anticoagulants. Currently, the treatment options for the management of direct oral anticoagulant (DOAC)-associated bleeding are limited. Prothrombin complex concentrates (PCCs) have been proposed as a potential therapeutic option, and evidence regarding their use is increasing.

Review

Many studies supporting PCC have used preclinical models and healthy volunteers; however, more recently, observational studies have further improved insight into current DOAC reversal strategies. Multiple clinical practice guidelines now specifically suggest use of PCCs for this indication. Specific reversal agents for Factor Xa inhibitors may become available in the near future, but data on their efficacy are still emerging.

Conclusions

Ultimately, a multimodal approach may be the optimal strategy to restore haemostasis in patients presenting with DOAC-associated coagulopathy.

Electronic supplementary material

The online version of this article (10.1186/s12245-018-0215-6) contains supplementary material, which is available to authorized users.

Pharmacological reversal of the direct oral anticoagulants-A comprehensive review of the literature

The direct oral anticoagulants (DOACs) are used for stroke prevention in atrial fibrillation (SPAF) and the prevention and treatment of venous thromboembolic disease (VTE). Although DOAC-associated bleeding events are less frequent as compared to vitamin K antagonists, there is significant concern surrounding physicians' ability to evaluate and manage DOAC-associated bleeding when it does occur. Idarucizumab is a specific reversal agent for dabigatran and is the agent of choice for dabigatran reversal in the setting of major bleeding or urgent surgery/procedures. There are no commercially available specific reversal agents for the direct Xa inhibitors. Although they have not been rigorously studied in DOAC-treated patients requiring urgent anticoagulant reversal, limited evidence from in vitro studies, animal bleeding models, human volunteer studies (in vivo and in vitro) and case series suggest that coagulation factor replacement with prothrombin complex concentrate (PCC) and activated PCC (FEIBA) may contribute to hemostasis. However, the safety and efficacy of these agents and the optimal dosing strategies remain uncertain.

Direct oral anticoagulants (DOAC) - Management of emergency situations

The worldwide increase in the aging population and the associated increase in the prevalence of atrial fibrillation and venous thromboembolism as well as the widespread use of direct oral anticoagulants (DOAC) have resulted in an increase of the need for the management of bleeding complications and emergency operations in frail, elderly patients, in clinical practice. When severe bleeding occurs, general assessment should include evaluation of the bleeding site, onset and severity of bleeding, renal function, and concurrent medications with focus on anti-platelet drugs and nonsteroidal anti-inflammatory drugs (NSAID). The last intake of the DOAC and its residual concentration are also relevant. The site of bleeding should be immediately localized, anticoagulation should be interrupted, and local measures to stop bleeding should be taken. In life-threatening bleeding or emergency operations immediate reversal of the antithrombotic effect may be indicated. If relevant residual DOAC-concentrations are expected and surgery cannot be postponed, prothrombin complex concentrate (PCC) and/or a specific antidote should be given. While idarucizumab, the specific antidote for dabigatran, has been recently approved for clinical use, the recombinant factor X protein andexanet alfa, an antidote for the reversal of inhibitors of coagulation factor Xa, and ciraparantag, a universal antidote, are not available. Future cohort studies are necessary to assess the efficacy and safety of specific and unspecific reversal agents in "real-life" conditions. This was the rationale for introducing the RADOA-registry (RADOA: Reversal Agent use in patients treated with Direct Oral Anticoagulants or vitamin K antagonists), a prospective non-interventional registry, which will evaluate the effects of specific and unspecific reversal agents in patients with life-threatening bleeding or emergency operations either treated with DOACs or vitamin K antagonists.

The reversal effect of prothrombin complex concentrate (PCC), activated PCC and recombinant activated factor VII in apixaban-treated patients in vitro

BACKGROUND

The number of patients under treatment with FXa inhibitors is increasing, but there is no concensus on how to reverse their anticoagulant effect in case of a life-threatening bleeding. A specific antidote is not yet commercially available. Prothrombin complex concentrate (PCC), activated PCC (aPCC) and recombinant factor VIIa (rFVIIa) are suggested available reversal agents.

OBJECTIVES

To find the most effective reversal agent to apixaban and to determine the optimal dose.

PATIENTS/METHODS

PCC, aPCC, and rFVIIa at concentrations imitating 80%, 100%, and 125% of suggested therapeutic doses were added to blood drawn from apixaban-treated patients (n=30). aPCC was also tested in a 50% dose. Samples from healthy subjects (n=40) were used as controls. Thromboelastometry in whole blood (WB) and thrombin generation in platelet-poor plasma (PPP) were measured to assess the reversal effect.

RESULTS

aPCC shortened clotting time (CT) in WB, and increased the peak thrombin concentration and velocity index in PPP to a greater extent than PCC and rFVIIa. No significant differences were seen between rFVIIa and aPCC on thrombin generation lag time, or between PCC and aPCC on endogenous thrombin potential (ETP). The 50% dose of aPCC had a slightly inferior effect, but was comparable to the other reversal agents.

CONCLUSIONS

In this in vitro study the 80% dose of aPCC (40 IU/kg) reversed the anticoagulant effect of apixaban more effectively than the corresponding dose of rFVIIa and PCC both in WB (CT) and PPP (peak, ETP).

The reversal effect of prothrombin complex concentrate (PCC), activated PCC and recombinant activated factor VII against anticoagulation of Xa inhibitor

Background

An increasing number of patients are treated with direct-acting oral anticoagulants (DOACs), but the optimal way to reverse the anticoagulant effect is not known. Specific antidotes are not available and prothrombin complex concentrate (PCC), activated PCC (aPCC) and recombinant factor VIIa (rFVIIa) are variously used as reversal agents in case of a major bleeding. We aimed to determine the most effective haemostatic agent and dose to reverse the effect of rivaroxaban in blood samples from patients taking rivaroxaban for therapeutic reasons.

Methods

Blood samples from rivaroxaban-treated patients (n = 50) were spiked with PCC, aPCC and rFVIIa at concentrations imitating 80%, 100% and 125% of suggested therapeutic doses. The reversal effect was assessed by thromboelastometry in whole blood and a thrombin generation assay (TGA) in platelet-poor plasma. Samples from healthy subjects (n = 40) were included as controls.

Results

In thromboelastometry measurements, aPCC and rFVIIa had a superior effect to PCC in reversing the rivaroxaban-induced lenghtening of clotting time (CT). aPCC was the only haemostatic agent that shortened the CT down to below the control level. Compared to healthy controls, patients on rivaroxaban also had a prolonged lag time and decreased peak concentration, velocity index and endogenous thrombin potential (ETP) in platelet-poor plasma. aPCC reversed these parameters more effectively than rFVIIa and PCC. There were no differences in efficacy between 80%, 100% and 125% doses of aPCC.

Conclusions

aPCC seems to reverse the anticoagulant effect of rivaroxaban more effectively than rFVIIa and PCC by evaluation with thromboelastometry and TGA in vitro.

The various assays for measuring activity states of factor VIIa in plasma and therapeutic products: Diagnostic value and analytical usefulness in various pathophysiological states

The key coagulation factor FVII, and its activated form FVIIa, present a major interest for their role at the initiation phase of blood coagulation, and because they can activate all blood coagulation cascade, through the extrinsic, but also the intrinsic pathway. Blood activation initiated through FVII is first presented, as it is understood nowadays. Measurement of FVII and FVIIa were of main interest for epidemiological studies, but FVIIa contribution to assay results was only deduced. The introduction of specific FVIIa assays, functional or immunoassays, allowed measuring directly FVIIa without any interference of non-activated FVII, or other coagulation factors or their activated forms. The various methods available, and their characteristics are presented, with a special focus on two assays developed by our group for FVIIa (a clotting one and a chromogenic one). The FVIIa clotting assay shows evident superiority for measuring its activity in plasma, in pathophysiological conditions. The normal range is <2.5ng/ml, which represents less than 0.5% of the FVII protein. FVIIa is elevated in some pathological states. The chromogenic assay is of interest for assigning the potency of FVIIa concentrates, as it has a higher dynamic range. Both assays are fully automatable on laboratory instruments, and standardized in a satisfactory manner thanks to the use of the FVIIa concentrate WHO International Standard (NIBSC). The various applications and usefulness of FVIIa laboratory assays are discussed, for the measurement of therapeutic products, or for following recoveries in treated patients, including hemophiliacs with inhibitors, patients with severe bleeding risk (liver diseases, surgery, trauma, …), and lastly for measurement of its activity in therapeutic products.

Management of Bleeding With Non-Vitamin K Antagonist Oral Anticoagulants in the Era of Specific Reversal Agents

Vitamin K antagonists are commonly used by clinicians to provide anticoagulation to patients who have or are at risk of having thrombotic events. In addition to familiarity with the dosing and monitoring of vitamin K antagonists, clinicians are accustomed to using vitamin K if there is a need to reverse the anticoagulant effect of vitamin K antagonists. There are now 4 new non-vitamin K antagonist oral anticoagulants (NOACs) that are attractive alternatives to vitamin K antagonists. Despite similar or lower rates of serious bleeding with NOACs in comparison with warfarin, there is a pressing need for strategies to manage bleeding when it does occur with NOACs and to reverse the pharmacological effect of these agents if needed. Important steps in minimizing bleeding risks with NOACs include dose adjustment of the agents in the setting of renal dysfunction and avoidance of the concomitant use of other antithrombotic agents if feasible. Laboratory measurement of the anticoagulant effect of NOACs is best accomplished with specialized assays, although some of the more widely available coagulation tests can provide information that is potentially useful to clinicians. Nonspecific hemostatic agents such as prothrombin complex concentrates and recombinant factor VIIa can be used to reverse the effect of NOACs. More specific reversing agents include the approved humanized monoclonal antibody fragment idarucizumab for reversing the effects of dabigatran, the investigational factor Xa decoy andexanet alfa, and the synthetic small molecule ciraparantag. Both andexanet and ciraparantag have been reported to reverse the effects of the anti-Xa NOACs (rivaroxaban, apixaban, and edoxaban), and a number of other anticoagulant agents in common clinical use, as well.

Ex vivo reversal of effects of rivaroxaban evaluated using thromboelastometry and thrombin generation assay

Background

In major bleeding events, the new direct oral anticoagulants pose a great challenge for physicians. The aim of the study was to test for ex vivo reversal of the direct oral anticoagulant rivaroxaban with various non-specific reversal agents: prothrombin complex concentrate (PCC), activated prothrombin complex concentrate (aPCC), recombinant activated factor VII (rFVIIa), and fibrinogen concentrate (FI).

Methods

Blood was obtained from healthy volunteers and from patients treated with rivaroxaban. Blood samples from healthy volunteers were spiked with rivaroxaban to test the correlation between rivaroxaban concentration and coagulation tests. Patient blood samples were spiked with various concentrations of the above-mentioned agents and analysed using thromboelastometry and thrombin generation.

Results

When added in vitro, rivaroxaban was significantly (P<0.05) correlated with ROTEM^® thromboelastometry EXTEM (extrinsic coagulation pathway) clotting time (CT), time to maximal velocity (MaxV−t), and with all measured thrombin generation parameters. In vivo, CT, MaxV−t, lag time, and peak thrombin generation (C_max) were significantly correlated with rivaroxaban concentrations. Regarding reversal of rivaroxaban, all tested agents significantly (P<0.05) reduced EXTEM CT, but to different extents: rFVIIa by 68%, aPCC by 47%, PCC by 17%, and FI by 9%. Only rFVIIa reversed EXTEM CT to baseline values. Both PCC (+102%) and aPCC (+232%) altered overall thrombin generation (area under the curve) and increased C_max (+461% for PCC, +87.5% for aPCC).

Conclusions

Thromboelastometry and thrombin generation assays do not favour the same reversal agents for rivaroxaban anticoagulation. Controlled clinical trials are urgently needed to establish doses and clinical efficacy of potential reversal agents.

Clinical trial registration

EudracCT trial no. 213-00474-30.

Venous thromboembolism in Latin America: a review and guide to diagnosis and treatment for primary care

There are various region-specific challenges to the diagnosis and effective treatment of venous thromboembolism in Latin America. Clear guidance for physicians and patient education could improve adherence to existing guidelines. This review examines available information on the burden of pulmonary embolism and deep vein thrombosis in Latin America and the regional issues surrounding the diagnosis and treatment of pulmonary embolism and deep vein thrombosis. Potential barriers to appropriate care, as well as treatment options and limitations on their use, are discussed. Finally, an algorithmic approach to the diagnosis and treatment of venous thromboembolism in ambulatory patients is proposed and care pathways for patients with pulmonary embolism and deep vein thrombosis are outlined for primary care providers in Latin America.

Managing target-specific oral anticoagulant associated bleeding including an update on pharmacological reversal agents

Target-specific oral anticoagulants (TSOACs) dabigatran, rivaroxaban and apixaban are approved for the prevention and treatment of thromboembolism in several clinical settings. Bleeding is the major complication of anticoagulant therapy, including TSOACs, and anticoagulant reversal strategies are highly desired for the management of anticoagulant-associated major bleeding in addition to maximum supportive care and procedural/surgical intervention. Unlike VKAs for which vitamin K and coagulation factor replacement with prothrombin complex concentrate (PCC) can restore hemostasis, there are no clinically available agents proven to reverse TSOAC anticoagulant effect and ameliorate TSOAC-related major bleeding. This narrative review critically evaluates the evidence for TSOAC reversal using non-specific reversal agents PCC, activated PCC (APCC) and recombinant activated factor VII (rVIIa) which have been assessed primarily using in vitro experiments, animal models and healthy human volunteers. Aripazine is a novel agent undergoing clinical development for non-specific anticoagulant reversal, including TSOACs. Data are presented regarding specific reversal agents idarucizumab (dabigatran) and andexanet alfa (oral factor Xa inhibitors) currently being evaluated in clinical trials. A practical approach to management of patients with TSOAC-associated bleeding is also provided. There is an urgent need for clinical studies that evaluate the efficacy and safety of reversal strategies for TSOAC-related major bleeding with assessment of clinical outcomes such as bleeding and mortality.

Reversal Strategies for Intracranial Hemorrhages in Patients Taking Oral Factor Xa Inhibitors

Factor Xa (fXa) inhibitors are becoming more common in clinical practice due to a variety of reasons. Unfortunately, limited data are currently available on the safe and efficacious reversal of these agents. This series presents 3 patient cases of intracranial hemorrhage and illustrates the observed effect of different methodologies undertaken in an attempt to reverse the fXa inhibitors implicated. Additionally, a brief review of the current available literature in reversal strategies is provided. The appropriate reversal for fXa inhibitors at this time is unknown. The cases described indicate that the administration of fresh frozen plasma and 4-factor prothrombin complex concentrate may provide minimal benefit in reversing the coagulation abnormalities caused by fXa inhibitors. However, in a life-threatening situation, the addition of these agents should be considered to prevent further progression of the bleed.

Reversal of rivaroxaban anticoagulation by nonactivated prothrombin complex concentrate in urgent surgery

Rivaroxaban is a once-daily oral anticoagulant currently indicated for the prevention of stroke and systemic embolism in patients with nonvalvular atrial fibrillation. It is also indicated for the prevention and treatment of venous or pulmonary thromboembolism. Despite the known advantages of rivaroxaban over standard therapy, this treatment is not exempt from bleeding. We present the case of a 51-year-old woman with arterial hypertension and paroxysmal atrial fibrillation anticoagulated with rivaroxaban 20 mg o.d. Patient was admitted to the emergency department because of intense abdominal pain, high temperature, hypotension, tachycardia and a big tumor in the right abdominal area. The ultrasonic exam showed a big collection in the thoracic and abdominal area, compatible with hematoma. Due to clinical instability, urgent surgery was required. Based on the results of coagulation parameters (PT: 17.5 s), the time from the last rivaroxaban dose was taken, and the patient weight, nonactivated prothrombin complex concentrate at a single dose of 1000 IU was administrated intravenously 1 h before the surgery. PT value decreased to normal value (13.5 s), and surgery was performed without any bleeding complication. The management of patients treated with rivaroxaban who require urgent surgery is discussed in this report.

Reversal of oral factor Xa inhibitors by prothrombin complex concentrates: a re-appraisal

Oral factor Xa inhibitors are an attractive class of anticoagulants expected to have broad application. Rapid and reliable reversal of the anticoagulant effect is important for patients with bleeding complications or those in need of urgent reversal for procedures. While no specific reversal agent is yet available, multiple published clinical guidelines suggest that four-factor prothrombin complex concentrates (PCC) should be considered when urgent reversal is desired. This presentation updates prior reviews on this topic (Crit Care, 17, 2013, 230; Thromb Haemost, 111, 2014, 189; J Thromb Thrombolysis, 2015, 39, 395); and summarizes more recent evidence in human studies indicating that four-factor PCCs available in North America do not reverse oral factor Xa-inhibitor anticoagulants. New agents on the horizon appear to be far more promising as therapies for reversal or oral factor Xa inhibitors.