Multimodal assessment of non-specific hemostatic agents for apixaban reversal

In vitro effects of Gla-domainless factor Xa analog on procoagulant and fibrinolytic pathways in apixaban-treated plasma and whole blood

BACKGROUND

Andexanet alfa is a Gla-domainless FXa (GDXa) analog used as an antidote to FXa inhibitors. Despite its clinical use, laboratory monitoring for anti-Xa reversal and the effect of andexanet on fibrinolysis has not been explored. We used a GDXa with a serine-to-alanine mutation at position 195 (chymotrypsin numbering) to model the interaction between andexanet and apixaban.

METHODS

Six batches of pooled plasma, and whole blood from healthy volunteers were treated with increasing concentrations of apixaban with/without GDXa. Thrombin generation and plasmin generation (TG and PG) were tested in plasma, and whole blood thrombus formation was tested using thromboelastometry or a flow-chamber system. FXa was also tested in isolation for its ability to support plasmin activation with/without apixaban and GDXa.

RESULTS

Apixaban (250-800 nM) concentration-dependently decreased the velocity and peak of TG in plasma. Apixaban prolonged the onset of thrombus formation in thromboelastometry and flow-chamber tests. GDXa normalized apixaban-induced delays in TG and whole blood thrombus formation. However, GDXa minimally affected the low PG velocity and peak caused by apixaban at higher concentrations (500-800 nM). FXa promoted plasmin generation independent of fibrin that was inhibited by apixaban at supratherapeutic concentrations.

CONCLUSIONS

This study demonstrated the feasibility of assessing coagulation lag time recovery in plasma and whole blood following in vitro apixaban reversal using GDXa, a biosimilar to andexanet. In contrast, GDXa-induced changes in plasmin generation and fibrinolysis were limited in PG and tPA-added ROTEM assays, supporting the endogenous profibrinolytic activity of FXa and its inhibition at elevated apixaban concentrations.

Effect of PCC on Thrombin Generation among Patients on Factor Xa Inhibitors with Major Bleeding or Needing Urgent Surgery (GAUGE): Design and Rationale

Background  Direct factor Xa inhibitors (FXaIs) account for most oral anticoagulant use and FXaI-associated bleeding events are common. Clinicians have variable national and regional access to specific FXaI reversal agents such as andexanet alfa. Many centers have adopted the use of prothrombin complex concentrates (PCCs) as hemostatic therapy for FXaI-associated major bleeding events. PCC does not impact circulating FXaI levels and its mechanism of action to achieve hemostasis in FXaI-associated bleeding is uncertain. While PCC increases quantitative thrombin generation assay (TGA) parameters, it does not correct FXaI-altered thrombin generation kinetics, nor does it normalize thrombin generation. Clinical data supporting the use of PCC are based on cohort studies reporting clinical hemostatic efficacy, which is difficult to measure. The benefits of PCC for FXaI-associated bleeding beyond supportive care are uncertain. Objective  GAUGE is a prospective observational study designed to measure the effects of four-factor PCC administration (Octaplex) on TGA parameters among patients with FXaI-associated bleeding or needing urgent surgery. Methods  Laboratory outcomes will include the mean paired change in TGA parameters from pre- to post-PCC administration and the proportion of participants whose post-PCC TGA values fall within a defined reference range. Clinical outcomes will include hemostatic efficacy, thromboembolic complications, and all-cause death at 30 days post-PCC. Conclusion  Development of a viable and universally accessible FXaI bleed management strategy is crucial. GAUGE will provide in vivo data on the effects of PCC among patients with FXaI-associated bleeding.

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.

A Historical Perspective on the Reversal of Anticoagulants

There has been a landmark shift in the last several decades in the management and prevention of thromboembolic events. From the discovery of parenteral and oral agents requiring frequent monitoring as early as 1914, to the development of direct oral anticoagulants (DOACs) that do not require monitoring or dose adjustment in the late 20th century, great advances have been achieved. Despite the advent of these newer agents, bleeding continues to be a key complication, affecting 2 to 4% of DOAC-treated patients per year. Bleeding is associated with substantial morbidity and mortality. Although specific reversal agents for DOACs have lagged the release of these agents, idarucizumab and andexanet alfa are now available as antagonists. However, the efficacy of these reversal agents is uncertain, and complications, including thrombosis, have not been adequately explored. As such, guidelines continue to advise the use of nonspecific prohemostatic agents for patients requiring reversal of the anticoagulant effect of these drugs. As the indications for DOACs and the overall prevalence of their use expand, there is an unmet need for further studies to determine the efficacy of specific compared with nonspecific pro-hemostatic reversal agents. In this review, we will discuss the evidence behind specific and nonspecific reversal agents for both parenteral and oral anticoagulants.

Rapid Detection of Apixaban by a ROTEM-Based Approach and Reversibility with Andexanet Alfa or DOAC-Stop

Background  A rapid test to detect apixaban treatment would be useful in acute situations such as major bleeding, urgent surgery, or in acute thrombosis.

Objective  This article aims to study if the viscoelastic test rotational thromboelastometry (ROTEM) can rapidly detect apixaban in whole blood using modified triggers based on factor Xa (FXa) or Russell viper venom (RVV).

Method  ROTEM clotting time (CT) was measured in samples from 40 patients on apixaban treatment, and in vitro in samples spiked with apixaban (20–500 ng/mL). Commercially available trigger Ex-tem was compared with modified triggers based on FXa or RVV. Reversibility of apixaban in the samples was studied; CT was measured with and without addition of DOAC-Stop or andexanet alfa, respectively, and the difference in CT was calculated (CT _diff ).

Results  Using FXa as trigger, we detected apixaban concentrations at 20 ng/mL and above with 100% sensitivity and 100% specificity in patient samples and in vitro. Corresponding data for Ex-tem were 92% sensitivity and 100% specificity in patients, and 94% sensitivity and 100% specificity in vitro, and for RVV 97% sensitivity and 94% specificity in patients, and 97% sensitivity and 100% specificity in vitro, respectively. CT _diff data were similar. Patient sample data were obtained within 20 minutes from sampling.

Conclusion  Apixaban at low therapeutic concentrations was detected within 20 minutes, and with high sensitivity and specificity. A trigger based on FXa outperformed the commercial trigger Ex-tem and a trigger based on RVV. ROTEM with a FXa-based trigger is a promising method to detect apixaban bedside in acute settings.

"In Less than No Time": Feasibility of Rotational Thromboelastometry to Detect Anticoagulant Drugs Activity and to Guide Reversal Therapy

Anticoagulant drugs (i.e., unfractionated heparin, low-molecular-weight heparins, vitamin K antagonists, and direct oral anticoagulants) are widely employed in preventing and treating venous thromboembolism (VTE), in preventing arterial thromboembolism in nonvalvular atrial fibrillation (NVAF), and in treating acute coronary diseases early. In certain situations, such as bleeding, urgent invasive procedures, and surgical settings, the evaluation of anticoagulant levels and the monitoring of reversal therapy appear essential. Standard coagulation tests (i.e., activated partial thromboplastin time (aPTT) and prothrombin time (PT)) can be normal, and the turnaround time can be long. While the role of viscoelastic hemostatic assays (VHAs), such as rotational thromboelastometry (ROTEM), has successfully increased over the years in the management of bleeding and thrombotic complications, its usefulness in detecting anticoagulants and their reversal still appears unclear.

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.

Factor VIII Inhibitor Bypassing Activity (FEIBA) Reversal for Apixaban and Rivaroxaban in Patients With Acute Intracranial and Nonintracranial Hemorrhage

BACKGROUND

The clinical use of factor VIII inhibitor bypassing activity (FEIBA) for factor Xa (FXa) inhibitor reversal is derived from small studies with notable variation in patient eligibility for use, dosage regimens, concurrent supportive care, and outcome measures. Consequently, additional effectiveness and safety data are warranted to expand the literature evaluating FEIBA for FXa inhibitor reversal.

OBJECTIVE

This study sought to determine the incidence of observed effective hemostasis within 24 hours of post-FEIBA® administration as well as in-hospital and 30-day post-discharge incidences of thromboembolic event (TEE) and mortality between apixaban and rivaroxaban in the intracranial hemorrhage (ICH) and non-ICH populations.

METHODS

This case series evaluated patients between January 1, 2014 through July 1, 2019 who received at least one FEIBA® dose for apixaban or rivaroxaban reversal secondary to acute ICH or non-ICH. Patient demographics, FEIBA® dosages, adjunct treatments, effectiveness, and safety outcomes were retrospectively collected from electronic medical record review. Modified hemostasis outcomes, adapted from criteria previously published by Sarode et al., TEE, and mortality between apixaban and rivaroxaban in the ICH and non-ICH populations were evaluated.

RESULTS

Among the 104 patients evaluated, 62 received apixaban and 42 rivaroxaban. Thirty apixaban and 25 rivaroxaban users experienced ICH, whereas 32 apixaban and 17 rivaroxaban users experienced non-ICH. Among the combined ICH and non-ICH populations, effective hemostasis occurred in 89%, TEE in 8%, and mortality in 13%. No statistically significant differences were observed within ICH and non-ICH populations receiving apixaban or rivaroxaban regarding effective hemostasis, TEE, or mortality.

CONCLUSION AND RELEVANCE

The combined ICH and non-ICH overall rates of effective hemostasis, TEE, and mortality were comparable to preexisting studies of FEIBA for factor Xa inhibitor reversal. The limitations inherent to the study design warrant a randomized controlled trial with an active comparator to confirm these observations.

Activated prothrombin complex concentrates for direct oral anticoagulant-associated bleeding or urgent surgery: Hemostatic and thrombotic outcomes

INTRODUCTION

Studies evaluating the use of activated prothrombin complex concentrates (aPCCs) for DOAC-associated bleeding are sparse.

MATERIALS AND METHODS

We conducted a retrospective study of patients receiving aPCC for DOAC-associated bleeding or for pre-operative optimization of hemostasis prior to urgent surgery. The primary efficacy outcome was hemostatic efficacy, the primary safety outcome was the 30-day thromboembolic complication rate.

RESULTS

Eighty-two patients were included in the analysis; 14 patients on dabigatran, 39 patients on rivaroxaban and 29 patients on apixaban. Fifty-four patients received aPCC for major bleeding and 28 patients prior to urgent surgery. Mean aPCC dosing was 2974 IU (SD ± 857 IU). Hemostasis was deemed effective by ISTH criteria in 50% of cases and "Good" or "Moderate" by Sarode criteria in 45.2% and 14.3% of cases, respectively. Surgical hemostasis was rated as "Normal" in 84% of cases pre-operative administration. Median pre-aPCC INR was 1.6 (IQR 0.5) and median post-aPCC INR was 1.2 (IQR 0.2) (p < 0.00001). Median pre-aPCC aPTT was 36 s (IQR 12.8), median post-aPCC aPTT was 29 s (IQR 9.8) (p = 0.0001). The 30-day thromboembolic event rate was 6.1%.

CONCLUSION

Further study is needed to characterize the hemostatic effects and thromboembolic risk of aPCC among patients with DOAC-associated bleeding or for attempted normalization of hemostasis prior to urgent surgery.

Correlation of Thromboelastography with Apparent Rivaroxaban Concentration: Has Point-of-Care Testing Improved?

BACKGROUND

Concern remains over reliable point-of-care testing to guide reversal of rivaroxaban, a commonly used factor Xa inhibitor, in high-acuity settings. Thromboelastography (TEG), a point-of-care viscoelastic assay, may have the ability to detect the anticoagulant effect of rivaroxaban. The authors ascertained the association of apparent rivaroxaban concentration with thromboelastography reaction time, i.e., time elapsed from blood sample placement in analyzer until beginning of clot formation, as measured using TEG and TEG6S instruments (Haemonetics Corporation, USA), hypothesizing that reaction time would correlate to degree of functional factor Xa impairment.

METHODS

The authors prospectively performed a diagnostic accuracy study comparing coagulation assays to apparent (i.e., indirectly assessed) rivaroxaban concentration in trauma patients with and without preinjury rivaroxaban presenting to a single center between April 2016 and July 2018. Blood samples at admission and after reversal or 24 h postadmission underwent TEG, TEG6S, thrombin generation assay, anti-factor Xa chromogenic assay, prothrombin time (PT), and ecarin chromogenic assay testing. The authors determined correlation of kaolin TEG, TEG6S, and prothrombin time to apparent rivaroxaban concentration. Receiver operating characteristic curve compared capacity to distinguish therapeutic rivaroxaban concentration (i.e., greater than or equal to 50 ng/ml) from nontherapeutic concentrations.

RESULTS

Eighty rivaroxaban patients were compared to 20 controls. Significant strong correlations existed between rivaroxaban concentration and TEG reaction time (ρ = 0.67; P < 0.001), TEG6S reaction time (ρ = 0.68; P < 0.001), and prothrombin time (ρ = 0.73; P < 0.001), however reaction time remained within the defined normal range for the assay. Rivaroxaban concentration demonstrated strong but not significant association with coagulation assays postreversal (n = 9; TEG reaction time ρ = 0.62; P = 0.101; TEG6S reaction time ρ = 0.57; P = 0.112) and small nonsignificant association for controls (TEG reaction time: ρ = -0.04; P = 0.845; TEG6S reaction time: ρ = -0.09; P = 0.667; PT-neoplastine: ρ = 0.19; P = 0.301). Rivaroxaban concentration (area under the curve, 0.91) and TEG6S reaction time (area under the curve, 0.84) best predicted therapeutic rivaroxaban concentration and exhibited similar receiver operating characteristic curves (P = 0.180).

CONCLUSIONS

Although TEG6S demonstrates significant strong correlation with rivaroxaban concentration, values within normal range limit clinical utility rendering rivaroxaban concentration the gold standard in measuring anticoagulant effect.

Prise en charge hémostatique des hémorragies cérébrales sous anticoagulants oraux

L’hématome intracrânien spontané a un pronostic clinique sévère. Le devenir des patients dépend de l’efficacité de la prise en charge initiale. L’importance du saignement, le volume de l’hématome et son évolution sont les facteurs principaux qui contrôlent mortalité et morbidité. Les traitements anticoagulants oraux, antivitamines K (AVK) et anticoagulants oraux directs (AOD), favorisent l’expansion de l’hématome. La correction rapide de l’hémostase permet le contrôle partiel de l’hématome. Alors que la réversion des AVK par les concentrés de complexe prothrombinique (CCP) a fait l’objet de recommandations bien diffusées, l’attitude thérapeutique reste peu codifiée avec les AOD, alliant l’utilisation de l’idarucizumab pour le dabigatran et des CCP pour les anti-Xa qui n’ont, pour l’instant, pas d’antidote.

Exploring the effect of factor Xa inhibitors on rotational thromboelastometry: a case series of bleeding patients

Direct oral anticoagulants (DOACs) have become the standard for thromboembolic risk management. In cases of major bleeding, trauma, or urgent surgery, accurate monitoring of DOAC activity is desirable; however, there is often no rapid, readily available test. We therefore explored the degree to which DOAC activity correlated with two coagulation assays: rotational thromboelastometry (ROTEM) and a standard coagulation assay in bleeding patients. We conducted a retrospective review of patients who experienced bleeding while on DOAC therapy from 2015 to 2017 at a Level 1 trauma center. ROTEM (EXTEM-clotting time {CT} in seconds), activated partial thromboplastin time (aPTT) (in seconds), prothrombin time (PT) (in seconds), DOAC specific drug test (anti-Xa and Hemoclot in ng/mL), and relevant clinical parameters were recorded. Descriptive statistics (median, range) and Spearman correlation coefficients were estimated. Differences between correlations were tested using Williams' t test. Twelve cases were reviewed (13 separate bleeding episodes). Sixteen measurements of DOAC activity, EXTEM-CT, and PT were obtained. The correlations with rivaroxaban activity were 0.96 and 0.86 (p = 0.2062) for PT and EXTEM-CT, respectively. The correlations with apixaban activity were 0.63 and 0.56 (p = 0.7175) for PT and EXTEM-CT, respectively. Analyses were not conducted for dabigatran due to limited data. Although not statistically significant, PT appears to have a higher correlation with direct Xa inhibitor activity than EXTEM-CT. Further research with larger samples is necessary to clarify the differences between ROTEM and standard assays in detecting DOAC activity.

Treprostinil treatment decreases circulating platelet microvesicles and their procoagulant activity in pediatric pulmonary hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) results from pulmonary vascular disease and may eventually lead to right heart failure and death. Vasodilator therapy has greatly improved PAH prognosis. Circulating microvesicles are considered as surrogate markers of endothelial and hematopoietic cell activation.

AIM

Thus, our purpose was to determine if MVs are upregulated in pediatric PAH such as reported in adult patients, and to analyze the impact of vasodilator therapies on MV count and function.

PATIENTS

Population study consisted of 26 patients of median age 6.09 years, with Congenital Heart Disease (CHD) and elevated pulmonary vascular resistance (CHD-PAH) or idiopathic PAH (iPAH).

RESULTS

Compared to healthy controls, all circulating MV subpopulations were found higher in untreated PAH patients. No significant differences of annexin-V+ total MV, endothelial, or leukocyte derived-MV counts were found between untreated patients and those receiving oral vasodilator therapies. Conversely, platelet MVs were significantly lower in the group treated with SC-treprostinil compared with both untreated PAH and oral therapy groups (P = 0.01), and exhibited a significant decrease of phospholipid procoagulant activity. Control samples treated in vitro with treprostinil at therapeutic concentrations showed as expected a significant decrease of platelet aggregation but also a reduced spontaneous MV generation.

CONCLUSION

Our results suggest that treprostinil, besides vasodilation, might exert its beneficial effect through an inhibition of platelet activation, resulting in a decreased number and procoagulant activity of circulating MVs.

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.

Laboratory Assessment of the Anticoagulant Activity of Apixaban in Patients With Nonvalvular Atrial Fibrillation

Our aim is to determine the most appropriate laboratory tests, besides anti-factor Xa (anti-FXa) chromogenic assays, to estimate the degree of anticoagulation with apixaban and compare it with that of rivaroxaban in real-world patients. Twenty patients with nonvalvular atrial fibrillation treated with apixaban 5 mg twice daily and 20 patients on rivaroxaban 20 mg once daily were studied. Conventional coagulation tests, thrombin generation assay (TGA), and thromboelastometry (nonactivated TEM [NATEM] assay) were performed in the 40 patients and 20 controls. The anti-FXa chromogenic assays were used to measure apixaban and rivaroxaban plasma levels. The NATEM measurements showed no significant difference between the 2 groups of patients. Concerning TGA, endogenous thrombin potential (ETP) was significantly decreased in patients on rivaroxaban as compared to those treated with apixaban (P < .003). A statistically significant, strong inverse correlation between apixaban plasma concentrations and ETP (P < .001) was observed. Apixaban significantly reduces ETP compared to controls, but to a lesser extent than rivaroxaban. Thrombin generation assay might provide additional information on apixaban exposure, which is required in order to individualize treatment especially for patients with a high bleeding risk. Our findings have to be further investigated in studies with larger sample sizes, in the entire range of apixaban exposure, with other direct oral anticoagulants, and in relation to clinical outcomes.

Rivaroxaban and apixaban induce clotting factor Xa fibrinolytic activity

Essentials Activated clotting factor X (FXa) acquires fibrinolytic cofactor function after cleavage by plasmin. FXa-mediated plasma fibrinolysis is enabled by active site modification blocking a second cleavage. FXa-directed oral anticoagulants (DOACs) alter FXa cleavage by plasmin. DOACs enhance FX-dependent fibrinolysis and plasmin generation by tissue plasminogen activator.

BACKGROUND

When bound to an anionic phospholipid-containing membrane, activated clotting factor X (FXa) is sequentially cleaved by plasmin from the intact form, FXaα, to FXaβ and then to Xa33/13. Tissue-type plasminogen activator (t-PA) produces plasmin and is the initiator of fibrinolysis. Both FXaβ and Xa33/13 enhance t-PA-mediated plasminogen activation. Although stable in experiments using purified proteins, Xa33/13 rapidly loses t-PA cofactor function in plasma. Bypassing this inhibition, covalent modification of the FXaα active site prevents Xa33/13 formation by plasmin, and the persistent FXaβ enhances plasma fibrinolysis. As the direct oral anticoagulants (DOACs) rivaroxaban and apixaban bind to the FXa active site, we hypothesized that they similarly modulate FXa fibrinolytic function.

METHODS

DOAC effects on fibrinolysis and the t-PA cofactor function of FXa were studied in patient plasma, normal pooled plasma and purified protein experiments by the use of light scattering, chromogenic assays, and immunoblots.

RESULTS

The plasma of patients taking rivaroxaban showed enhanced fibrinolysis correlating with FXaβ. In normal pooled plasma, the addition of rivaroxaban or apixaban also shortened fibrinolysis times. This was related to the cleavage product, FXaβ, which increased plasmin production by t-PA. It was confirmed that these results were not caused by DOACs affecting activated FXIII-mediated fibrin crosslinking, clot ultrastructure and thrombin-activatable fibrinolysis inhibitor activation in plasma.

CONCLUSION

The current study suggests a previously unknown effect of DOACs on FXa in addition to their well-documented anticoagulant role. By enabling the t-PA cofactor function of FXaβ in plasma, DOACs also enhance fibrinolysis. This effect may broaden their therapeutic indications.

Activated prothrombin complex concentrate to reverse the factor Xa inhibitor (apixaban) effect before emergency surgery: a case series

BACKGROUND

The lack of an antidote against factor Xa inhibitors in case of major bleeding or need for urgent surgery is a concern to clinicians. Guidelines on managing major bleeding in patients under anticoagulation with a factor Xa inhibitor suggest several hemostatic agents to reverse the effect, but there is no consensus regarding the choice of drug or appropriate dose. The ability of prothrombin complex concentrate, activated prothrombin complex concentrate, and recombinant factor VIIa to reverse the effect of factor Xa inhibitors has been evaluated in animal studies, in vitro studies, and healthy volunteers, but not yet in randomized clinical studies.

CASE PRESENTATION

We report a consecutive case series of patients under factor Xa inhibitor (apixaban) treatment who received activated prothrombin complex concentrate to reverse the anticoagulation effect before emergency cardiovascular surgery. Patient 1, a 63-year-old white man, was operated with replacement of the aortic valve; patient 2, a 65-year-old white man, underwent heart transplantation; patient 3, a 68-year-old white man, was operated for acute type A aortic dissection. They all received activated prothrombin complex concentrate 25 IU/kg immediately before surgery. In two of the cases, the global coagulation assay thromboelastometry (ROTEM™) was performed before and after administering activated prothrombin complex concentrate. The ROTEM™ clotting time was reduced from 1900 seconds to 740 seconds and from 1482 to 807 seconds, respectively, after administering a dose of 25 IU/kg activated prothrombin complex concentrate. The apixaban concentration before reversal was within the range considered to be the therapeutic level in all cases. No bleeding complications occurred during surgery, but one case was complicated with bleeding postoperatively. No thromboembolic complications were observed during or after surgery.

CONCLUSIONS

Activated prothrombin complex concentrate 25 IU/kg reversed the anticoagulation effect of apixaban effectively and safely before emergency cardiovascular surgery.

Reversal of apixaban induced alterations in haemostasis by different coagulation factor concentrates in patients after hip or knee replacement surgery

BACKGROUND

Apixaban is a direct oral anticoagulant (DOAC) with a specific inhibition of activated factor X (FXa). In case of bleeding or need of urgent surgery a direct antidote is not yet available. Off-label application of non-specific haemostatic agents, such as prothrombin complex concentrate (PCC) and recombinant FVIIa (rFVIIa), has been reported to reverse the effects of apixaban in in vitro and animal studies. The aim of this study is to measure the reversal potential of PCC and rFVIIa in patients with prophylactic apixaban concentrations.

MATERIAL AND METHODS

Whole blood from patients under prophylactic therapy with apixaban was spiked with two doses of PCC or rFVIIa. Thromboelastometry (ROTEM^®), prothrombin time (PT), and activated partial prothrombin time (aPTT) were performed.

RESULTS

Prolongations in PT and aPTT were corrected by the different concentrates with variable efficacies (PCC<rFVIIa) for all time points after medication. Compared with baseline, the reversal effects ranged from partial correction (PCC) to overcorrection of the CT-ExTEM, PT and aPTT by rFVIIa.

DISCUSSION

PCC partially reverses the effect of apixaban as measured by point-of-care coagulation testing and standard coagulation tests. Only rFVIIa reliably reverses apixaban anticoagulation.

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.

Edoxaban: Impact on routine and specific coagulation assays

Assessment of plasma concentration/effect of edoxaban may be useful in some situations. Also, clinicians need to know how routine coagulation assays are influenced. It was our aim to determine coagulation tests useful for the assessment of edoxaban’s pharmacodynamics and provide recommendations for the interpretation of haemostasis diagnostic tests. Edoxaban was spiked at concentrations ranging from 0 to 1,000 ng/ml in platelet-poor plasma which covers the on-therapy range (from ± 25 ng/ml at Ctrough to ± 170 ng/ml at Cmax). aPTT, PT, dRVVT, chromogenic anti-Xa assays, TGA and a large panel of haemostasis diagnostic tests were performed using several reagents. A concentration-dependent prolongation of aPTT, PT and dRVVT was observed. The effect was dependent on the reagents. FXa chromogenic assays showed high sensitivity and a linear correlation depending on the methodology. TGA may be useful to assess the pharmacodynamics of edoxaban but its turnaround time and the lack of standardisation are limitations. Edoxaban impairs the assessment of lupus anticoagulant, protein S (clotting method), APC-R, antithrombin (FXa-based assay) and measurement of clotting factor activity. Immunological assays and assays acting below the FXa are not influenced by edoxaban. In conclusion, some PT reagents could be used to estimate edoxaban activity. Chromogenic anti-Xa assays are required to assess the plasma concentration. TGA may be useful but requires standardisation. In case of thrombophilia or in the exploration of a haemorrhagic event, immunological assays should be recommended, when applicable. Standardisation of the time between the last intake and the sampling is mandatory to provide a proper assessment of the result.

Supplementary Material to this article is available online at www.thrombosis-online.com.

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).

Laboratory Assessment of the Anticoagulant Activity of Direct Oral Anticoagulants: A Systematic Review

BACKGROUND

Direct oral anticoagulants (DOACs) are the treatment of choice for most patients with atrial fibrillation and/or noncancer-associated venous thromboembolic disease. Although routine monitoring of these agents is not required, assessment of anticoagulant effect may be desirable in special situations. The objective of this review was to summarize systematically evidence regarding laboratory assessment of the anticoagulant effects of dabigatran, rivaroxaban, apixaban, and edoxaban.

METHODS

PubMed, Embase, and Web of Science were searched for studies reporting relationships between drug levels and coagulation assay results.

RESULTS

We identified 109 eligible studies: 35 for dabigatran, 50 for rivaroxaban, 11 for apixaban, and 13 for edoxaban. The performance of standard anticoagulation tests varied across DOACs and reagents; most assays, showed insufficient correlation to provide a reliable assessment of DOAC effects. Dilute thrombin time (TT) assays demonstrated linear correlation (r2 = 0.67-0.99) across a range of expected concentrations of dabigatran, as did ecarin-based assays. Calibrated anti-Xa assays demonstrated linear correlation (r2 = 0.78-1.00) across a wide range of concentrations for rivaroxaban, apixaban, and edoxaban.

CONCLUSIONS

An ideal test, offering both accuracy and precision for measurement of any DOAC is not widely available. We recommend a dilute TT or ecarin-based assay for assessment of the anticoagulant effect of dabigatran and anti-Xa assays with drug-specific calibrators for direct Xa inhibitors. In the absence of these tests, TT or APTT is recommended over PT/INR for assessment of dabigatran, and PT/INR is recommended over APTT for detection of factor Xa inhibitors. Time since last dose, the presence or absence of drug interactions, and renal and hepatic function should impact clinical estimates of anticoagulant effect in a patient for whom laboratory test results are not available.

Nonvitamin K antagonist oral anticoagulant activity: challenges in measurement and reversal

Background

Four nonvitamin K antagonist oral anticoagulants (NOACs) are approved for the prevention of stroke in patients with nonvalvular atrial fibrillation and for the treatment of venous thromboembolism. These include the direct thrombin inhibitor dabigatran and the direct factor Xa inhibitors rivaroxaban, apixaban, and edoxaban. Bleeding is a complication for all anticoagulants and concerns regarding bleeding risk and the suitability of effective reversal strategies may be a barrier to their prescription. Despite the reduced risk of bleeding compared with vitamin K antagonists, questions persist regarding the management of bleeding related to NOAC use.

Main text

To date, although a number of assays are responsive to NOACs, no single routine laboratory test has been identified to accurately measure the clinical anticoagulation state of patients on NOACs or established as a reliable predictor of bleeding risk. In addition, the establishment of a reliable human bleeding model to test novel inhibitors of the coagulation cascade has proved challenging. Although routine monitoring of anticoagulant levels is not necessary in patients taking NOACs, anticoagulant reversal and a means of measuring reversal may be required for patients who present with bleeding or require urgent surgery. Prothrombin complex concentrates are pooled plasma products containing varying amounts of inactive vitamin K-dependent clotting factors in addition to vitamin K-dependent proteins and can replenish factors in the intrinsic and extrinsic coagulation cascade, reversing an anticoagulant effect. Only one agent, idarucizumab, has been approved for rapid reversal of dabigatran-induced anticoagulation and one more agent, andexanet alfa, has been submitted for approval to reverse the anticoagulatory effects of direct and indirect factor Xa inhibitors.

Conclusions

This review discusses the laboratory tests available for assessing anticoagulation, human models of bleeding, and the use of current strategies—including prothrombin complex concentrates for reversal of anticoagulation by NOACs—to manage bleeding in patients.

Measurement and reversal of the direct oral anticoagulants

Direct oral anticoagulants (DOACs) offer noninferior efficacy and improved safety compared to vitamin K antagonists (VKAs) for the prevention and treatment of venous thromboembolism and for the prevention of stroke and systemic embolism in nonvalvular atrial fibrillation. Unlike VKAs, DOACs do not require routine laboratory monitoring of anticoagulant effect and dose adjustment. In certain situations, however, laboratory assessment of anticoagulant effect may be desirable. Here we review the utility of currently available assays for assessment of DOAC effect and recommend an optimal assessment strategy for each drug, including calibrated dilute thrombin time or ecarin-based assays for dabigatran and calibrated anti-Xa activity assays for the factor Xa inhibitors. We also discuss reversal strategies, both specific and nonspecific, for each drug, including the preferential use of idarucizumab for the reversal of dabigatran and two agents, andexanet and ciraparantag, currently under development for the reversal of rivaroxaban, apixaban, and edoxaban.

Four-factor prothrombin complex concentrate for life-threatening bleeds or emergent surgery: A retrospective evaluation

PURPOSE

Previous trials investigating usage of four-factor prothrombin complex concentrate (4F-PCC) excluded patients with various thrombotic risk factors. The objective of this study was to evaluate the safety and effectiveness of 4F-PCC in a real-world setting based on an institutional protocol that does not have strict exclusion criteria.

METHODS

This was a retrospective study of adult patients who received 4F-PCC. The primary outcome was a confirmed thromboembolism within 14 days after 4F-PCC administration. Secondary outcomes included international normalized ratio (INR) correction to <1.5 at first draw and incidence of INR rebound for patients undergoing reversal of warfarin and hemostatic effectiveness for patients experiencing a bleed.

RESULTS

Ninety-three patients received 4F-PCC. Sixty-three (67.7%) were reversed for bleeding and 30 (32.3%) for surgery. Eleven patients (11.8%) developed a thromboembolism within 14 days. The median (interquartile range) time to event was 5 (2-7) days. Significant risk factors were heparin-induced thrombocytopenia (P= .01) and major surgery within 14 days (P= .02), as well as the presence of >6 thrombotic risk factors (P= .01). For patients post-warfarin reversal, 45/63 (71.4%) achieved INR correction at first draw, 55/63 (87.3%) achieved INR correction within 24 hours, and 14/55 (25.5%) experienced INR rebound. Of these 14 patients, 8 (57.1%) did not receive concomitant vitamin K.

CONCLUSIONS

4F-PCC was associated with a notable thromboembolic risk. All patient-specific risk factors should be considered prior to administration. 4F-PCC remains a useful agent for warfarin reversal. Lack of concomitant vitamin K may contribute to INR rebound.

Reversibility of Apixaban Anticoagulation with a Four-Factor Prothrombin Complex Concentrate in Healthy Volunteers

It was hypothesized that the four-factor prothrombin complex concentrate (4F-PCC) Kcentra 25 unit/kg would reverse impairment of thrombin generation in healthy volunteers dosed with apixaban to steady state. In this randomized, two-period crossover, assessor-blinded trial, 12 healthy subjects received 5 mg apixaban every 12 h. Three h after the fifth dose, four-factor prothrombin complex concentrate (4F-PCC) 25 unit/kg or saline were infused. Serial blood samples were assessed for thrombin generation using PPP-reagent and PPP-reagent low, anti-Xa, PT, and PTT assays. Geometric mean ratio was calculated at 30 min postinfusion, and at 24, 48, and 72 h. Peak thrombin generation was 76% higher at 30 min postinfusion with 4F-PCC (p = 0.025). The difference declined to 24% at 24 h and resolved by 48 h. Other thrombin generation parameters were also partially normalized. There was no difference between 4F-PCC and saline in anti-Xa assessment at 30 min or later time points.

In vivo increase in thrombin generation by four-factor prothrombin complex concentrate in apixaban-treated healthy volunteers

BACKGROUND

Four-factor prothrombin complex concentrate (PCC) (Cofact; Sanquin Blood Supply) 50 IU kg(-1) increased thrombin generation beyond baseline values in healthy, rivaroxaban-treated subjects.

OBJECTIVE

To assess whether infusion with doses of 37.5 IU kg(-1) and 25 IU kg(-1) PCC reverses the anticoagulant effect of high-dose apixaban, another oral direct factor Xa inhibitor.

METHODS

In a randomized, double-blind, placebo-controlled, crossover study, six healthy subjects received twice-daily apixaban 10 mg for 3.5 days followed by a single bolus of 37.5 IU kg(-1) PCC, 25 IU kg(-1) PCC, or placebo. The primary outcome was the effect of PCC 15 min after infusion on thrombin generation (endogenous thrombin potential [ETP]); secondary outcomes were the immediate effect of PCC on prothrombin time (PT) and the effect of PCC as compared with placebo over a period of 24 h on ETP and PT.

RESULTS

Fifteen minutes after infusion of 37.5 IU kg(-1) and 25 IU kg(-1) PCC, ETP increased from 41% ± 11% to 56% ± 23% (P = 0.06) and from 44% ± 12% to 51% ± 15% (P = 0.03), respectively. ETP significantly differed over time between 37.5 IU kg(-1) PCC and placebo during 24 h after infusion (P < 0.01). Both PCC doses restored apixaban-induced PT prolongation after 15 min (P < 0.01), and this was sustained over a period of 24 h.

CONCLUSION

Both 37.5 IU kg(-1) PCC and 25 IU/kg PCC improved coagulation parameters in healthy subjects, suggesting partial reversal of the anticoagulant effect of apixaban. This implies that PCC might be considered in patients with apixaban-associated bleeding. However, ETP was not immediately restored to pre-apixaban levels, suggesting that these doses are too low to instantly and fully restore hemostasis at peak apixaban levels.

Practical management of bleeding in patients receiving non-vitamin K antagonist oral anticoagulants

Non-vitamin K antagonist oral anticoagulants (NOACs) are increasingly used in the prevention and treatment of venous thromboembolism and in the prevention of stroke in patients with non-valvular atrial fibrillation. In phase III clinical trials and meta-analyses, the NOACs were at least as effective as vitamin K antagonists (VKAs) and were associated with a similar or lower incidence of major bleeding, including consistent and significant decreases in intracranial bleeding, although with an increase in gastrointestinal bleeding for some agents compared with VKAs. Subsequent real-world evidence supports these outcomes. Despite this, physicians have concerns about serious bleeding or emergencies because there are no specific reversal agents for the NOACs. However, in clinical trials, patients receiving NOACs generally had similar or better outcomes after these events than those taking VKAs. As with any bleeding, anticoagulant-related bleeding should first be stratified according to severity and location; risk can be minimised by ongoing assessment. Management protocols for NOAC-related bleeding are similar to those for VKAs but should take into account the pharmacological profile of the specific drug. Because of their short half-lives, NOAC-related mild bleeding can often be controlled by temporarily withholding treatment. More severe bleeding requires standard escalating haemodynamic support measures, and non-specific reversal agents can be considered in life-threatening situations, based on limited clinical data. Specific and rapid reversal agents are not currently available for any oral anticoagulant and restoration of coagulation may not necessarily lead to better outcomes. Nevertheless, specific NOAC reversal agents are in development and show promise in healthy volunteers.

How the direct oral anticoagulant apixaban affects thrombin generation parameters

BACKGROUND AND OBJECTIVES

Apixaban is a direct oral anticoagulant (DOAC) targeting factor Xa and thus quenching thrombin generation and clot formation. However, little information is available on the influence that apixaban may have on the parameters of thrombin generation.

METHODS

Aliquots of a pooled normal plasma have been added with increased concentrations of purified apixaban and were used to assess the degree of modification brought about by the drug on the basic tests of coagulation prothrombin and activated partial thromboplastin time (PT and APTT) and on thrombin generation parameters.

RESULTS

The study shows that while apixaban has little effect on PT or APTT it does affect all the parameters of thrombin generation, including the lag-time (which is increased), the endogenous thrombin potential (ETP) and thrombin-peak (both decreased although to a different extent), and the velocity index (decreased). Interestingly, the above effects were more pronounced when the measurements were recorded in the presence of thrombomodulin, thus making the ratio (with/without thrombomodulin) to decrease consistently as a function of the apixaban concentrations.

CONCLUSIONS

These findings support the antithrombotic properties of apixaban and can help to understand the mechanism(s) of action of this drug. Thrombin generation could be used as a convenient laboratory tool to assess the anticoagulant activity of other drugs and to make between-DOAC comparison.