Emicizumab promotes factor Xa generation on endothelial cells.

BACKGROUND: Until recently, the treatment of hemophilia A relied on factor (F)VIII replacement. However, up to one-third of patients with severe hemophilia A develop neutralizing alloantibodies that render replacement therapies ineffective. The development of emicizumab, a bispecific antibody that partially mimics FVIIIa, has revolutionized the treatment of these patients. However, the use of an activated prothrombin complex concentrate [FEIBA (Takeda)] to treat breakthrough bleeding in patients on emicizumab has been associated with thrombotic complications including a unique microangiopathy. OBJECTIVES: We hypothesized that the thrombotic complications observed with the combination of emicizumab and FEIBA might be due to excessive expression of procoagulant activity on the surface of endothelial cells. METHODS: We examined the ability of emicizumab to promote FX activation on endothelial cells using 2 cell culture models. RESULTS: We found that endothelial cells readily support emicizumab-mediated activation of FX by FIXa. The level of FXa generation depends on the concentration of available FIXa. The addition of FEIBA to emicizumab increased FXa generation in a dose-dependent manner on endothelial cells in both models. The rate of FXa generation was further enhanced by endothelial cell activation. However, unlike emicizumab, we found limited FXa generation in the presence of FVIII(a), which followed a significant lag time and was not dependent on FIXa concentration under these conditions. CONCLUSION: Emicizumab promotes FXa generation on the surface of endothelial cells, which is markedly enhanced in the presence of FEIBA. These findings demonstrate a potential mechanism for the thrombotic complications seen with the combined use of emicizumab and FEIBA.

Study on the Relationship between Rivaroxaban and Factor Xa Activity in Blood Based on HPLC-MS/MS.

OBJECTIVE: The aim of the study was to investigate a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for the determination of rivaroxaban and evaluate the correlation between plasma concentration and anti-Xa activity in patients using oral rivaroxaban. METHODS: In this study, the plasma concentration of rivaroxaban and anti-Xa factor activities was determined in 125 patients, and the relationship between the two variables was analysed by SPSS 21.0 software. RESULTS: The results showed that the plasma concentrations of oral rivaroxaban patients were significantly correlated with the activity of the anti-Xa factor (Spearman's r = 0.990, P < 0.05). CONCLUSION: The plasma concentrations of rivaroxaban are a potentially useful monitoring indicator to assess the patient's bleeding risk if testing for plasma anti-Xa activity is not available.

Retrospective Comparison of Andexanet Alfa and 4-Factor Prothrombin Complex for Reversal of Factor Xa-Inhibitor Related Bleeding.

The aim of this retrospective study was to compare andexanet alfa and 4-factor prothrombin complex (4F-PCC) for reversal of factor Xa (FXa)-inhibitor bleeding. Patients that received andexanet alfa for reversal were included. An equivalent number of patients administered 4F-PCC for FXa-inhibitor bleeding were randomly selected as historical controls. The primary outcome was effective hemostasis achievement within 12 h, defined using ANNEXA-4 criteria. Thromboembolic events and mortality within 30 days were also evaluated. A total of 32 patients were included. Baseline characteristics were not statistically different between andexanet alfa (n = 16) and 4F-PCC (n = 16). Intracranial bleeding was the primary reversal indication in 43.8% versus 62.5% of patients, respectively. Effective hemostasis was reached in 75.0% of andexanet alfa patients compared to 62.5% of 4F-PCC patients (P = .70). Thromboembolic events occurred in 4 (25.0%) patients and 3 (18.8%) patients, respectively (P = .99). Mortality incidence was 12.5% and 31.3%, respectively (P = .39). Andexanet alfa and 4F-PCC attained hemostasis in a majority of patients. A high, but a similar rate of thromboembolic events was seen with both treatments. Prospective studies are needed to elucidate comparative risks and benefits of the 2 agents.

Procoagulant activities of skeletal and cardiac muscle myosin depend on contaminating phospholipid.

Recent reports indicate that suspended skeletal and cardiac myosin, such as might be released during injury, can act as procoagulants by providing membrane-like support for factors Xa and Va in the prothrombinase complex. Further, skeletal myosin provides membrane-like support for activated protein C. This raises the question of whether purified muscle myosins retain procoagulant phospholipid through purification. We found that lactadherin, a phosphatidyl-l-serine-binding protein, blocked >99% of prothrombinase activity supported by rabbit skeletal and by bovine cardiac myosin. Similarly, annexin A5 and phospholipase A2 blocked >95% of myosin-supported activity, confirming that contaminating phospholipid is required to support myosin-related prothrombinase activity. We asked whether contaminating phospholipid in myosin preparations may also contain tissue factor (TF). Skeletal myosin supported factor VIIa cleavage of factor X equivalent to contamination by ∼1:100 000 TF/myosin, whereas cardiac myosin had TF-like activity >10-fold higher. TF pathway inhibitor inhibited the TF-like activity similar to control TF. These results indicate that purified skeletal muscle and cardiac myosins support the prothrombinase complex indirectly through contaminating phospholipid and also support factor X activation through TF-like activity. Our findings suggest a previously unstudied affinity of skeletal and cardiac myosin for phospholipid membranes.

Novel factor Xa inhibitor, maslinic acid, with antiplatelet aggregation activity.

As antithrombotic effects of maslinic acid (MA) have not yet been studied, MA-mediated downregulation of coagulation factor Xa (FXa) and platelet aggregation was studied. We show that MA inhibited the enzymatic activity of FXa and platelet aggregation, induced by adenosine diphosphate (ADP) and a thromboxane A2 (TXA2 ) analog, U46619 with a similar antithrombotic efficacy to rivaroxaban, a direct FXa inhibitor used as a positive control. Mechanistically, MA suppressed U46619- or ADP-induced phosphorylation of myristoylated alanine-rich C kinase substrate, and the expression of P-selectin, and activated PAC-1 in platelets. MA increased generation of nitric oxide, but downregulated excessive secretion of endothelin-1 in ADP- or U46619-treated human umbilical vein endothelial cells. In arterial and pulmonary thrombosis mouse model, MA showed prominent anticoagulant and antithrombotic effects. Our data suggest MA as a candidate molecule for a new class of drugs targeting anti-FXa and antiplatelet.

Apixaban exhibits anti-arthritic effects by inhibiting activated factor X-mediated JAK2/STAT3 and MAPK phosphorylation pathways.

Activated factor X (FXa) is strongly linked to various inflammatory events. This study aimed to investigate the effect of FXa on janus kinase2/signal transducers and activators of transcription3 (JAK2/STAT3) and mitogen-activated protein kinase (MAPK) phosphorylation in relation to rheumatoid arthritis (RA). It also extends its scope to explore the possible anti-arthritic effects of apixaban, a selective FXa inhibitor. Rats were allocated into normal control; complete Freund's adjuvant (CFA, 0.4 ml/4 days/12 days); FXa (120 µg/kg/day/3 days) and CFA + FXa groups as well as three treated groups including CFA + apixaban; FXa + apixaban and CFA + FXa + apixaban. Apixaban was administered at a dose of 10 mg/kg/12 h for15 days. By the end of the experimental period, tissue samples were collected for the assessment of phosphorylated (p)-JAK2, STAT3, MAPK, matrixmetalloprotein-1 (MMP-1) and protease-activated receptor 2. Furthermore, Serum interleukin-6 (IL-6), platelet-derived growth factor (PDGF), anti-citrullinated protein antibody (ACPA), 8-hydroxy-2'-deoxyguanosine (8-OHdG), plasma level of FXa and prothrombin time were evaluated. In support, histopathological and macroscopical examinations were performed. FXa activated JAK2, STAT3 and MAPK phosphorylation through activation of PAR 2, PDGF and IL-6 and concomitantly led to a significant elevation in ACPA, MMP-1 and 8-OHdG. Apixaban markedly amended FXa-induced changes. Conclusively, the current study revealed that FXa may have a drastic role in RA progression and pathogenesis at least through stimulation of JAK2/STAT3 and MAPK phosphorylation. Furthermore, apixaban exerted robust arthro-protective effects. These beneficial outcomes could be attributed to its ability to impede JAK2/STAT3 and MAPK activation, as well as to its antioxidant property.

Anticoagulation Management and Antithrombin Supplementation Practice during Veno-venous Extracorporeal Membrane Oxygenation: A Worldwide Survey.

BACKGROUND: There is a lack of consensus on how to manage anticoagulation during veno-venous extracorporeal membrane oxygenation, including antithrombin monitoring and supplementation. The authors' aim was to determine current practice in a large number of extracorporeal membrane oxygenation centers around the world. METHODS: This was an electronic survey disseminated in 2018 to directors and coordinators of extracorporeal membrane oxygenation centers as well as to extracorporeal membrane oxygenation experts. Participating centers were classified according to some covariates that may affect practice, including 2017 gross national income per capita, primary patient population, and annual extracorporeal membrane oxygenation patient volume. RESULTS: The authors analyzed 273 unique responses from 50 countries. Systemic anticoagulation was routinely prescribed in 264 (96.7%) centers, with unfractionated heparin being the drug of choice in 255 (96.6%) of them. The preferred method to monitor anticoagulation was activated partial thromboplastin time in 114 (41.8%) centers, activated clotting time in 82 (30.0%) centers, and anti-factor Xa activity in 62 (22.7%) centers. Circulating antithrombin activity was routinely monitored in 133 (48.7%) centers. Antithrombin supplementation was routinely prescribed in 104 (38.1%) centers. At multivariable analyzes, routine antithrombin supplementation was associated with national income, being less likely in lower- than in higher-income countries (odds ratio, 0.099 [95% CI, 0.022 to 0.45]; P = 0.003); with primary patient population being more frequent in mixed (odds ratio, 2.73 [1.23 to 6.0]; P = 0.013) and pediatric-only centers (odds ratio, 6.3 [2.98 to 13.2]; P < 0.001) than in adult-only centers; but not with annual volume of extracorporeal membrane oxygenation cases, being similarly common in smaller and larger centers (odds ratio, 1.00 [0.48 to 2.08]; P = 0.997). CONCLUSIONS: There is large practice variation among institutions regarding anticoagulation management and antithrombin supplementation during veno-venous extracorporeal membrane oxygenation. The paucity of prospective studies and differences across institutions based on national income and primary patient population may contribute to these findings.

Nonhemostatic Activities of Factor Xa: Are There Pleiotropic Effects of Anti-FXa Direct Oral Anticoagulants?

Factor Xa (FXa) is the key serine protease of the coagulation cascade as it is the point of convergence of the intrinsic and extrinsic pathways, leading to the formation of thrombin. Factor Xa is an established target of anticoagulation therapy, due to its central role in coagulation. Over the past years, several direct oral anticoagulants (DOACs) targeting FXa have been developed. Rivaroxaban, apixaban, and edoxaban are used in clinical practice for prevention and treatment of thrombotic diseases. Increasing evidence suggests that FXa exerts nonhemostatic cellular effects that are mediated mainly through protease-activated receptors-1 and -2 and are involved in pathophysiological conditions, such as atherosclerosis, inflammation, and fibrosis. Direct inhibition of FXa by DOACs could be beneficial in these conditions. This is a narrative review that focuses on the cellular effects of FXa in various cell types and conditions, as well as on the possible pleiotropic effects of FXa-targeting DOACs.

Andexanet Alfa for Reversing Factor Xa Inhibition.

The direct oral anticoagulants (DOACs) have gained popularity recently among both patients and providers for their comparable or better efficacy and safety profiles compared with warfarin and the lack of need for routine monitoring of anticoagulant effect. One obstacle for the more widespread use of the DOACs in clinical practice has been the lack of a reversal agent. Most DOACs act by directly binding to and inhibiting the effects of factor Xa. Andexanet alfa (Andexxa, Portola Pharmaceuticals, San Francisco, CA) is a modified form of factor Xa that acts as a decoy binding entity for DOACs, thereby allowing endogenous factor Xa to perform its normal clotting functions. Andexanet has proven efficacious in clinical trials for reversing the anticoagulant effects of apixaban, edoxaban, and rivaroxaban, although its impact on clinical outcomes has not been adequately studied. Andexanet has a boxed warning for thromboembolic risks, ischemic risks, cardiac arrest, and sudden death, with these adverse events occurring in up to 18% of patients in clinical trials. However, the occurrence of these adverse events needs to be considered in relation to the fragile nature of patients who receive this agent. Because the duration of the DOACs is much less than that of warfarin, it is unclear how many patients would actually need andexanet in clinical practice, because cessation of the DOAC may be all that is needed to effectively manage bleeding. Nonetheless, having andexanet available in cases of DOAC-associated severe or life-threatening bleeding represents a therapeutic advance and should provide an added level of comfort with the clinical use of DOACs.

Antiplatelet and anticoagulant activities of two phospholipase A2s purified from Cerastes cerastes venom: Structure-function relationship.

This study aimed to elucidate anticoagulant/antiplatelet mechanisms of two previously purified PLA2 s from Cerastes cerastes venom, here, termed Cc1 -PLA2 and Cc2 -PLA2 . Both PLA2 s present close molecular weights of 13,534 and 13,430 Da and Isoectric pH (pI) 7.38 and 7.86 respectively, for Cc1 -PLA2 and Cc2 -PLA2 . These Ca2+ -dependent enzymes showed a high catalytic activity upon phospholipids, inducing indirect hemolysis, since they conserve the catalytic domain of PLA2 s 26 CYCGWGGKG34 . They exhibited dual inhibition of platelet aggregation by targeting P2 Y12 and TPα receptors preventing Adenosine diphosphate/arachidonate binding and blood clotting. These effects are due to the interaction of Cc1 -PLA2 s/Cc2 -PLA2 s with factor FXa through a noncatalytic PL-independent mechanism leading to nonreleased thrombin. Both proteins consist of 120 amino acid residues and share similar three-dimensional structures close to other SV-PLA2 s. Structural data of PLA2 s allowed the relevant residues involved in binding to FXa and platelet receptors. These findings may lead to the design of novel noncompetitive FXa inhibitors.

Rivaroxaban Levels in Patients' Plasmas are Comparable by Using Two Different Anti Xa Assay/Coagulometer Systems Calibrated with Two Different Calibrators.

BACKGROUND: Rivaroxaban oral anticoagulant does not need laboratory monitoring, but in some situations plasma level measurement is useful. The objective of this paper was to verify analytical performance and compare two rivaroxaban calibrated anti Xa assays/coagulometer systems with specific or other branch calibrators. METHODS: In 59 samples drawn at trough or peak from patients taking rivaroxaban, plasma levels were measured by HemosIL Liquid anti Xa in ACLTOP 300/500, and STA liquid Anti Xa in TCoag Destiny Plus. HemosIL and STA rivaroxaban calibrators and controls were used. CLSI guideline procedures EP15A3 for precision and trueness, EP6 for linearity, and EP9 for methods comparison were used. RESULTS: Coefficient of variation within run and total precision (CVR and CVWL respectively) of plasmatic rivaroxaban were < 4.2 and < 4.85% and BIAS < 7.4 and < 6.5%, for HemosIL-ACL TOP and STA-Destiny systems, respectively. Linearity verification 8 - 525 ng/mL a Deming regression for methods comparison presented R 0.963, 0.968 and 0.982, with a mean CV 13.3% when using different systems and calibrations. CONCLUSIONS: The analytical performance of plasma rivaroxaban was acceptable in both systems, and results from reagent/coagulometer systems are comparable even when calibrating with different branch material.

Establishment of prophylactic enoxaparin dosing recommendations to achieve targeted anti-factor Xa concentrations in children with CHD.

BACKGROUND: Enoxaparin may be used to prevent central venous catheter-related thrombosis in patients with CHD. We aimed to determine whether current enoxaparin dosing regimens effectively achieve anti-factor Xa concentrations within prophylactic goal ranges in this patient population. METHODS: We implemented a formal protocol aimed at reducing central venous catheter-related thrombosis in children with CHD in January, 2016. Standard empiric prophylactic enoxaparin dosing regimens were used - for example, 0.75 mg/kg/dose every 12 hours for patients <2 months of age and 0.5 mg/kg/dose every 12 hours for patients ⩾2 months of age - with anti-factor Xa goal range of 0.25-0.49 IU/ml. Patients <2 years of age who received enoxaparin and had at least one valid steady-state anti-factor Xa measurement between 25 January, 2016 and 31 August, 2016 were retrospectively reviewed. RESULTS: During the study period, 47 patients had 186 anti-factor Xa concentrations measured, of which 20 (11%) were above and 112 (60%) were below the prophylactic goal range. Anti-factor Xa concentrations within the goal range were ultimately achieved in 31 patients. Median dose required to achieve anti-factor Xa concentrations within the prophylactic range was 0.89 mg/kg/dose (25, 75%: 0.75, 1.11) for patients <2 months (n=23 patients) and 0.79 mg/kg/dose (25, 75%: 0.62, 1.11) for patients ⩾2 months (n=8 patients). CONCLUSIONS: Enoxaparin doses required to achieve prophylactic anti-factor Xa concentrations in young children with CHD were consistently higher than the currently recommended prophylactic dosing regimens. Further study is needed to determine whether dose titration to achieve prophylactic anti-factor Xa concentrations is effective in preventing central venous catheter-related thrombosis.

Anti-Xa activity in oral factor Xa inhibitor-treated patients with atrial fibrillation and a higher risk of bleeding: a pilot study.

: The number of patients with nonvalvular atrial fibrillation (NV-AF) who require long-term anticoagulation and also have a higher risk of bleeding is increasing. Recently, there is no information regarding real on-treatment anti-Xa activity in patients with NV-AF and a higher risk of bleeding who receive oral factor Xa inhibitors. The aim of this study was to determine trough and peak anti-Xa activity in these patients. This single-centre pilot study enrolled 41 patients with NV-AF and a higher risk of bleeding defined as Hypertension, Abnormal Renal/Liver Function, Stroke, Bleeding History or Predisposition, Labile INR, Elderly, Drugs/Alcohol Concomitantly score at least 3 points. Twenty-one patients were treated with rivaroxaban and 17 patients were treated with apixaban. The trough and peak samples of these patients were tested for anti-Xa activity with factor Xa-calibrated anti-Xa chromogenic analysis. The detected trough anti-Xa activity was 63.2 ±â€Š44.4 ng/ml. There was a significant increase in peak anti-Xa activity up to 170.3 ±â€Š99.6 ng/ml (P < 0.001) observed. There were no significant differences in trough (52.4 ±â€Š41.9 vs. 76.0 ±â€Š45.4 ng/ml; P = 0.12) and peak (187.2 ±â€Š122.5 vs. 151.5 ±â€Š64.0 ng/ml; P = 0.27) anti-Xa activity between rivaroxaban-treated and apixaban-treated patients. This study demonstrated the anti-Xa activity in oral factor Xa inhibitor-treated patients with NV-AF and a higher risk of bleeding. No significant differences in this activity between rivaroxaban-treated and apixaban-treated patients were found.

Factor X activating Atractaspis snake venoms and the relative coagulotoxicity neutralising efficacy of African antivenoms.

Atractaspis snake species are enigmatic in their natural history, and venom effects are correspondingly poorly described. Clinical reports are scarce but bites have been described as causing severe hypertension, profound local tissue damage leading to amputation, and deaths are on record. Clinical descriptions have largely concentrated upon tissue effects, and research efforts have focused upon the blood-pressure affecting sarafotoxins. However, coagulation disturbances suggestive of procoagulant functions have been reported in some clinical cases, yet this aspect has been uninvestigated. We used a suite of assays to investigate the coagulotoxic effects of venoms from six different Atractaspis specimens from central Africa. The procoagulant function of factor X activation was revealed, as was the pseudo-procoagulant function of direct cleavage of fibrinogen into weak clots. The relative neutralization efficacy of South African Antivenom Producer's antivenoms on Atractaspis venoms was boomslang>>>polyvalent>saw-scaled viper. While the boomslang antivenom was the most effective on Atractaspis venoms, the ability to neutralize the most potent Atractaspis species in this study was up to 4-6 times less effective than boomslang antivenom neutralizes boomslang venom. Therefore, while these results suggest cross-reactivity of boomslang antivenom with the unexpectedly potent coagulotoxic effects of Atractaspis venoms, a considerable amount of this rare antivenom may be needed. This report thus reveals potent venom actions upon blood coagulation that may lead to severe clinical effects with limited management strategies.

Betrixaban: a direct oral inhibitor of activated factor X for the prophylaxis of venous thromboembolism in patients hospitalized for acute medical illness.

Venous thromboembolism (VTE), comprising deep vein thrombosis and pulmonary embolism, is a serious clinical and public health concern. Hospitalization is a major risk factor for developing VTE. Hospital-associated events account for more than 50% of all cases of VTE. Heparins have demonstrated to be efficacious in the prevention of VTE in medically ill patients. Despite the demonstrated efficacy and safety of the available direct oral anticoagulants in the prevention and treatment of different thromboembolic conditions, their net benefit in the prevention of VTE in hospitalized medically ill patients has not been fully confirmed. Betrixaban is an oral, specific and direct inhibitor of human coagulation factor Xa with demonstrated efficacy and safety for the prevention of VTE in patients undergoing total knee replacement and in patients with nonvalvular atrial fibrillation. Recent studies have successfully evaluated betrixaban 80 mg once daily in the prevention of VTE in acute medically ill patients in a large phase III trial. This review will address preclinical pharmacology and main aspects of the clinical development of betrixaban as an antithrombotic agent, with specific attention to recent studies on the prophylaxis of VTE in a specific population of patients hospitalized for acute medical illnesses.

Practical Value of Anti-Xa Activity in the Evaluation of Extracorporeal Circuit Anticoagulation during Haemodialysis: Results of a Cross-Sectional Single-Centre Study.

BACKGROUND/AIMS: Anticoagulation of the extracorporeal circuit is essential for adequate haemodialysis (HD). Low molecular weight heparins (LMWHs) are safe and sufficient towards achieving this goal. In the Netherlands, dosage is based on bodyweight and adjusted based on clinical events. LMWH levels during dialysis can be quantified through measurement of the anti-Xa activity and a target range of 0.5-1.0 IU/mL has been proposed. We aimed to evaluate the practical value of the anti-Xa activity to guide LMWH dosage in HD patients. Additionally, the value of the activated partial thromboplastin time (APTT) was investigated. METHODS: All prevalent adult HD patients of our dialysis clinic were included. APTT and anti-Xa activity were measured before, during and after 2 dialysis sessions. Clinical and dialysis characteristics, including LMWH dosage, were derived from digital patient charts. RESULTS: Our final study cohort consisted of 83 patients. LMWH dosage during dialysis was appropriate for bodyweight in 61% of cases, of which 50% reached an anti-Xa activity within the putative target range of 0.5-1.0 IU/mL. Forty-six percent of patients had an anti-Xa activity >1.0 IU/mL. Anti-Xa levels during and after dialysis were significantly correlated (r = 0.803, p < 0.01). No thrombotic or haemorrhagic complications were observed in this study. Correlation of APTT with anti-Xa activity was poor. CONCLUSION: Anti-Xa activity measurements during dialysis can identify patients in whom LMWH dosage should be lowered in a subsequent dialysis session. Whether such an intervention leads to a decrease in haemorrhagic complications needs to be evaluated in prospective studies.

Anticoagulant activity of a natural protein purified from Hypomesus olidus.

A novel anticoagulant protein (E-II-1) was separated and purified from Hypomesus olidus, a unique freshwater fish in northern China. E-II-1 had a molecular mass of approximately 40 kDa with no subunits. The high content of hydrophobic amino acids and negatively charged amino acids in E-II-1 demonstrated that the amino acid compositions might contribute to the anticoagulant activity. E-II-1 contained α-helices 16.75%, ß-sheets 42.67%, ß-turn 25.58% and random coil 15.00%. In vitro blood coagulation time assay, E-II-1 significantly prolonged the activated partial thrombin time in a dose-dependent manner. Results indicated that E-II-1 acted as anticoagulants through the endogenous pathway with an inhibition of FXa. The specific activity of E-II-1 was 103.50 U/mg at a concentration of 1.00 mg/mL. Therefore, E-II-1 might be one of the promising anticoagulants originated from natural food sources with more safety and less side effects.

Evaluación de la anticoagulación con rivaroxaban, en pacientes con fibrilación auricular no valvular de reciente diagnóstico / Evaluation of oral anticoagulation with rivaroxaban, in patients with new onset non valvular atrial fibrillation

Background: Atrial fibrillation (AF) generates a hypercoagulable state with an increased thrombin generation and raised levels of thrombin-antithrombin complexes, which results in a high risk of stroke and thromboembolism. Aim: To evaluate the anticoagulant effect of rivaroxaban by anti-Xa factor activity and its correlation with thrombin-antithrombin complexes, thrombin generation and prothrombin time in patients newly diagnosed with non-valvular AF. Patients and Methods: Prospective study in patients with indication of anticoagulation. Demographic variables, cardiovascular risk factors, CHA2DS2-VASc and HAS-BLED scores were recorded. Blood samples were taken at baseline, at 3 and 24 hours after the administration of the drug and at 30 days. Rivaroxaban levels, anti-Xa activity, prothrombin time, thrombin generation and plasma levels of thrombin-antithrombin complexes were determined. Results: We studied 20 patients aged 76.3 ± 8.0 years (60% female) with a CHA2DS2-VASc score > 2 points. The anti-Xa factor activity correlated with rivaroxaban plasma levels at 3 hours (r = 0.61, p < 0.01), at 24 hours (r = 0.85, p < 0.01) and at 30 days (r = 0.99, p < 0.01), with prothrombin time at 3 hours (r = -0.86, p = 0.019) and at 30 days (r = -0.63, p = 0.02) and with a sustained decrease in thrombin generation at 30 days of follow-up (r = -0.74, p < 0.01). There was no correlation with thrombin-antithrombin complexes (r = -0.02, p = 0.83). Conclusions: Rivaroxaban consistently inhibited the mild pro-coagulant state found in newly diagnosed non-valvular AF patients through the first 24 hours and this effect was maintained at 30 days. Plasma levels of the drug correlated with anti-Xa factor activity, thrombin generation and prothrombin time

Anti-Xa activity in apixaban overdose: a case report.

INTRODUCTION: Apixaban is a novel oral anticoagulation agent that exerts its effect through direct factor Xa inhibition. We present a case of multi-drug overdose including apixaban with associated apixaban concentrations. CASE: A 53 year-old man presented to our metropolitan hospital following a deliberate self-poisoning with 200 mg apixaban, 35 mg ramipril, 105 mg bisoprolol, 280 mg atorvastatin, 6 mg colchicine, 37.4 mg magnesium, 4 × 500 mg paracetamol/9.5 mg codeine/5 mg phenylephrine and alcohol. He developed hypotension that was treated with noradrenaline. His initial and peak apixaban concentration was 1022.6 ng/ml and was associated with only minor bleeding from his femoral central line insertion site, which improved with local compression. Vitamin K 10 mg (at 9 h post-ingestion) and Prothrombinex-VF 2000 units (at 13 h post-ingestion) were also administered without any observed effect on coagulation studies. Apixaban elimination appeared to display first-order kinetics with an elimination half-life of 7.4 h. His plasma apixaban concentration was within the therapeutic dose range 10 h post-ingestion and he recovered uneventfully. CONCLUSION: A case of apixaban overdose with associated apixaban concentrations is presented. There was rapid resolution of anticoagulation with no demonstrable benefit of currently available clotting factor replacement.