Non-VKA Oral Anticoagulants: Accurate Measurement of Plasma Drug Concentrations

Pilot study on the probability of drug-drug interactions among direct oral anticoagulants (DOACs) and antiseizure medications (ASMs): a clinical perspective

BACKGROUND

There is little and controversial information about changes in plasma concentrations (PCs) or clinical events during coadministration of antiseizure medications (ASMs) and direct oral anticoagulants (DOACs). We aimed to explore possible determinants of dosage class among DOACs trough PCs when ASMs are co-administered and the relative risks. We also provided some clinical examples of patients' management.

METHODS

Data on adult patients concomitantly treated with ASMs (grouped in enzyme-inducing [I-ASMs], non-inducing [nI-ASMs], and levetiracetam [LEV]) and DOACs with at least one measurement of DOACs' PC were retrospectively collected. The role of DOAC-ASM combinations in predicting PC class (ranging from I at ischemic/thromboembolic risk to IV at increased bleeding risk) was investigated by an ordered logit model, and the marginal probabilities of belonging to the four dosage classes were calculated.

RESULTS

We collected 46 DOACs' PCs out of 31 patients. There were 5 (10.9%) determinations in class I (4 out of 5 with concomitant I-ASMs) and 5 (10.9%) in class IV. The rivaroxaban/I-ASM combination was associated with lower DOAC dosages than rivaroxaban/LEV (OR: 0.00; 95% CI: 0.00-0.62). Furthermore, patient's probability of being in class I was approximately 50% with the rivaroxaban/I-ASM combination, while apixaban, dabigatran, and edoxaban had the highest cumulative probability of being in class II or III despite the ASM used.

CONCLUSION

These preliminary results confirm the reduction of DOAC's PC by I-ASMs and suggest a better manageability of apixaban, dabigatran, and edoxaban independently from the concomitant ASM, whereas rivaroxaban seems the most liable to PC alterations with I-ASMs.

Stability of Direct Oral Anticoagulants Concentrations in Blood Samples for Accessibility Expansion of Chromogenic Assays

Background and Objectives: Direct oral anticoagulants (DOACs) are used for minimising the risk of thromboembolic events. In clinical practice, there is no need to measure DOAC concentration in the routine. Nevertheless, there are cases where such measurements are necessary, as the European Society of Cardiology's guideline recommends. However, determining DOAC levels is not available for everyone due to chromogenic assay availability limitations from sample storage problems, as tests are performed only in a few healthcare settings. This study aimed to assess whether more applicable storage conditions could be used for transportation to provide chromogenic assays for outpatient healthcare and other hospitals' practices. Materials and Methods: Chromogenic assays measuring anti-FXa (for rivaroxaban and edoxaban) and anti-FIIa (for dabigatran) were used. Concentrations were determined immediately after blood collection as baseline value: (1) after the storage of citrated whole blood in refrigerator (+2-8 °C); (2) of citrated plasma in refrigerator (+2-8 °C); and (3) of citrated frozen plasma (-20 °C) on the third and seventh days of storage. Acceptable change limits were considered stable if the deviation did not exceed ±20% of the baseline value. Results: The median (Cl 95%) baseline value of rivaroxaban was 168 (147-236) ng/mL; of dabigatran 139 (99-178) ng/mL; and of edoxaban-174 (135-259) ng/mL. The median deviation from a baseline value stored as citrate whole blood samples (+2-8 °C) was 5.4% and 3.4%; as citrated plasma (+2-8 °C) was 0.4% and -0.6%; and as citrated frozen plasma (-20 °C) was -0.2% and 0.2% on the third and seventh days of storage, respectively. Conclusions: Our data suggest that whole blood samples stored in a refrigerator, as well as citrated plasma samples stored in both the refrigerator and freezer, preserve DOAC concentration stable at +2-8 °C or -20 °C for up to 7 days, and are suitable for transportation, except for low-concentration samples.

Systemic metastasis-targeted nanotherapeutic reinforces tumor surgical resection and chemotherapy

Failure of conventional clinical therapies such as tumor resection and chemotherapy are mainly due to the ineffective control of tumor metastasis. Metastasis consists of three steps: (i) tumor cells extravasate from the primary sites into the circulation system via epithelial-mesenchymal transition (EMT), (ii) the circulating tumor cells (CTCs) form “micro-thrombi” with platelets to evade the immune surveillance in circulation, and (iii) the CTCs colonize in the pre-metastatic niche. Here, we design a systemic metastasis-targeted nanotherapeutic (H@CaPP) composed of an anti-inflammatory agent, piceatannol, and an anti-thrombotic agent, low molecular weight heparin, to hinder the multiple steps of tumor metastasis. H@CaPP is found efficiently impeded EMT, inhibited the formation of “micro-thrombi”, and prevented the development of pre-metastatic niche. When combined with surgical resection or chemotherapy, H@CaPP efficiently inhibits tumor metastasis and prolonged overall survival of tumor-bearing mice. Collectively, we provide a simple and effective systemic metastasis-targeted nanotherapeutic for combating tumor metastasis.

Failure of conventional clinical therapies such as tumor resection and chemotherapy are mainly due to the ineffective control of tumor metastasis. Here, the authors show that a systemic metastasis-targeted nanotherapeutic may offer a powerful adjunct therapy for suppressing tumor metastasis.

Direct Oral Anticoagulants Plasma Levels Measurement: Clinical Usefulness from Trials and Real-World Data

Measurement of direct oral anticoagulants (DOACs) activity is not routinely necessary. Indeed, evaluation of DOACs plasmatic concentration is discouraged for the majority of patients, due to the lack of outcome data supporting this approach. Nevertheless, DOAC measurements may be useful in emergency situations such as serious bleeding events, need for urgent invasive procedures, and acute ischemic stroke or in managing anticoagulation in "special populations" not adequately studied in clinical trials, for example the very elderly or those at the extremes of body weight. The aim of this review is to describe and summarize the methods for DOACs activity evaluation and the settings in which their plasma level measurement may be indicated, analyzing indications from scientific societies and evidence from clinical trials, as well as real world data on the usefulness of DOACs plasma levels "monitoring."

Can an anti-Xa assay for unfractionated heparin be used to assess the presence of rivaroxaban in critical situations?

OBJECTIVE

Although rivaroxaban has recently become widely used for thrombosis treatment, it is difficult for clinicians to make clinical decisions in critical situations, such as emergent surgery or interventions, because a specific anti-Xa assay is not available in many laboratories. This study assessed the relationships between rivaroxaban-specific anti-factor Xa activity (AXA) and unfractionated heparin (UFH)-specific AXA and determined the cutoff level for UFH-specific AXA in critical situations for patients undergoing rivaroxaban therapy.

METHODS

Thirty-eight blood samples were collected from patients with cancer-associated thrombosis receiving rivaroxaban therapy. All samples were assessed using both rivaroxaban-specific and UFH-specific anti-Xa assays. Routine coagulation studies, including prothrombin time (PT) and activated partial thromboplastin time, were also conducted on the samples.

RESULTS

A positive dose-dependent correlation between rivaroxaban-specific and UFH-specific AXA was evident (R = 0.97; P < .0001). Rivaroxaban-specific AXA was also positively correlated with PT (R = 0.95; P < .0001) but only weakly with activated partial thromboplastin time (R = 0.67; P < .0001). Patients with plasma rivaroxaban concentrations <100 ng/mL were found to have UFH-specific AXA <1.41 IU/mL and PT <17.3 seconds, with sensitivities of 100% and 93.3% and specificities of 87.0% and 95.7%, respectively.

CONCLUSIONS

Our study demonstrates that UFH-calibrated AXA correlates strongly with plasma rivaroxaban concentration. This assay appears to be sensitive to the presence of rivaroxaban, which may be advantageous in the setting of assessing drug levels for critical events. These findings suggest that if a rivaroxaban-specific anti-Xa assay is unavailable, the chromogenic anti-Xa assay for UFH may be useful to assess the anticoagulant effects of rivaroxaban.

Limitations of Specific Coagulation Tests for Direct Oral Anticoagulants: A Critical Analysis

Background

During treatment with direct oral anticoagulants (DOAC), coagulation assessment is required before thrombolysis, surgery, and if anticoagulation reversal is evaluated. Limited data support the accuracy of DOAC‐specific coagulation assays around the current safe‐for‐treatment threshold of 30 ng/mL.

Methods and Results

In 481 samples obtained from 96 patients enrolled at a single center, DOAC concentrations were measured using Hemoclot direct thrombin inhibitor assay, Biophen direct thrombin inhibitor assay or ecarin clotting time for dabigatran, chromogenic anti‐Xa assay (AXA) for factor Xa inhibitors (rivaroxaban, apixaban) and ultraperformance liquid chromatography–tandem mass spectrometry as reference. All dabigatran‐specific assays had high sensitivity to concentrations >30 ng/mL, but specificity was lower for Hemoclot direct thrombin inhibitor assay (78.2%) than for Biophen direct thrombin inhibitor assay (98.9%) and ecarin clotting time (94.6%). AXA provided high sensitivity and specificity for rivaroxaban, but low sensitivity for apixaban (73.8%; concentrations up to 82 ng/mL were misclassified as <30 ng/mL). If no DOAC‐specific calibration for AXA is available, results 2‐fold above the upper limit of normal indicate relevant rivaroxaban concentrations. For apixaban, all elevated results should raise suspicion of relevant anticoagulation.

Conclusions

DOAC‐specific tests differ considerably in diagnostic performance for concentrations close to the currently accepted safe‐for‐treatment threshold. Compared with Biophen direct thrombin inhibitor assay and ecarin clotting time, limited specificity of Hemoclot direct thrombin inhibitor assay poses a high risk of unnecessary anticoagulation reversal or treatment delays in patients on dabigatran. While AXA accurately detected rivaroxaban, the impact of low apixaban levels on the assay was weak. Hence, AXA results need to be interpreted with extreme caution when used to assess hemostatic function in patients on apixaban.

Clinical Trial Registration

URL: https://www.clinicaltrials.gov. Unique identifiers: NCT02371044, NCT02371070.

Drug levels and bleeding complications in atrial fibrillation patients treated with direct oral anticoagulants

Essentials Currently, DOACs are given at fixed doses and do not require laboratory monitoring. Direct oral anticoagulant-specific measurements were performed at trough and peak. Patients who developed bleeding events showed higher DOAC plasma levels at peak. This study suggests the need of a more accurate DOAC dose assessment.

BACKGROUND

Direct oral anticoagulants (DOACs) are administered at fixed dose. The aim of the study was to evaluate the relationship between DOAC C-trough or C-peak plasma levels and bleeding complications in patients with non-valvular atrial fibrillation (NVAF).

METHODS

Five hundred sixty five consecutive naive NVAF patients were enrolled. The DOAC measurements at C-trough and at C-peak (available in 411 patients) were performed at steady state, within the first month of treatment. Major bleeding (MB), clinically relevant non-major bleeding (CRNMB), and minor bleeding (MinB), occurring during 1 year of follow-up after blood sampling, were recorded. For each DOAC, interval of C-trough and C-peak levels was subdivided into four equal classes and results were attributed to these classes; the median values of results were also calculated.

RESULTS

Two hundred eight patients were on apixaban, 185 on dabigatran, and 172 on rivaroxaban. For 1-[qqqdeletezzz] year follow up for all patients, we observed: 19 MB (3.36%), 6 CRNMB (1.06%), and 47 MinB (8.31%). The prevalence of bleeding patients with anticoagulant levels in the upper classes of C-peak activity (II + III + IV) was higher than that in the lowest class. Normalized results of C-peak levels were higher in patients with bleeding than in those without bleeding.

CONCLUSIONS

Bleeding complications during DOAC treatment were more frequent among atrial fibrillation (AF) patients with higher C-peak anticoagulant levels. In addition to a previous study that showed an increased risk of thrombotic complications in the patients with low C-trough levels, this study seems to indicate that patients with NVAF on DOACs would need a more accurate definition of their optimal therapeutic window.

Management of major bleeding and outcomes in patients treated with direct oral anticoagulants: results from the START-Event registry

The management of major bleeding in patients treated with direct oral anticoagulants (DOACs) is still not well established. START-Events, a branch of the START registry (Survey on anTicoagulated pAtients RegisTer) (NCT02219984), aims to describe the actual management of bleeding or recurrent thrombotic events in routine clinical practice. We here present the results of the management of bleeding patients. The START-Event registry is a prospective, observational, multicenter, international study. Baseline characteristics (demographic, clinical, risk factors) of patients, laboratory data at admission and during follow-up, site of bleeding, therapeutic strategies, and outcomes at the time of hospital discharge and after 6 months were recorded on a web-based case report form. Between January 2015 and December 2016, 117 patients with major bleeding events were enrolled. Non-valvular atrial fibrillation (NVAF) was the indication for treatment in 84% (62% males); 53 patients had intracranial bleeding (13 fatal), 42 had gastrointestinal bleeding (1 fatal), and 22 had bleeding in other sites. Therapeutic interventions for the management of bleeding were performed in 71% of patients. Therapeutic strategies with/without surgery or invasive procedures included: fluid replacement or red blood cells transfusion, prothrombin complex concentrates (3 or 4 factors), antifibrinolytic drugs, and the administration of idarucizumab. Creatinine, blood cell count, and PT/aPTT were the most frequent tests requested, while specific DOAC measurements were performed in 23% of patients. Mortality during hospitalization was 11.9%, at 6-month follow-up 15.5%. Our data confirm a high heterogeneity in the management of bleeding complications in patients treated with DOACs.

Laboratory measurement of apixaban using anti-factor Xa assays in acute ischemic stroke patients with non-valvular atrial fibrillation

Apixaban is effective and safe for preventing stroke, and its usage has increased exponentially in recent years. However, data concerning the therapeutic range of apixaban is limited. This study determined the trough and peak levels of apixaban-specific anti-factor Xa activity (AFXaA) in acute ischemic stroke patients with non-valvular atrial fibrillation (NVAF) in Korea. The study included 85 patients who received apixaban. Blood samples were taken to measure the trough and peak levels of AFXaA using a chromogenic anti-factor assay, as well as prothrombin time (PT) and activated partial thromboplastin time (aPTT). We also reviewed complications such as major bleeding of patients treated with apixaban. In patients given a 5.0-mg apixaban dose, the median trough and peak levels of AFXaA were 104.5 and 202.0 ng/mL. In patients given a 2.5-mg apixaban dose, the median trough and peak AFXaA levels were 76.0 and 151.0 ng/mL. The PT showed a positive correlation with increased AFXaA activity at both levels (Trough R = 0.486, Peak R = 0.592), but the aPTT had no relationship with AFXaA activity at both levels (Trough R = 0.181, Peak R = 0.129). Two cases with intracranial bleeding belonged to the highest AFXaA quartile (Trough, p = 0.176; Peak, p = 0.053). In conclusion, we determined the trough and peak levels of AFXaA in patients with NVAF while being treated with the apixaban in Korea. Our results could be used as a starting point when setting the reference ranges for laboratories using anti-Xa assay. Large-scale studies are needed to establish the reference range for AFXaA in patients with NVAF.

Low drug levels and thrombotic complications in high-risk atrial fibrillation patients treated with direct oral anticoagulants

Essentials Direct oral anticoagulants (DOACs) do not require laboratory monitoring currently. DOAC specific measurements were performed at trough in patients with atrial fibrillation. Patients who developed thromboembolic events showed lower DOAC plasma levels. This study supports the concept of measuring DOAC levels at steady state.

SUMMARY

Background Direct oral anticoagulants (DOACs) are administered at fixed doses without the need for dose adjustment according to laboratory testing. High interindividual variability in drug blood levels has been shown with all DOACs. To evaluate a possible relationship between DOAC C-trough anticoagulant levels and thromboembolic events, 565 consecutive naive patients with atrial fibrillation (AF) were enrolled in this study performed within the START Laboratory Registry. Methods DOAC-specific measurements (diluted thrombin time or anti-activated factor II calibrated for dabigatran; anti-activated FX calibrated for rivaroxaban or apixaban) at C-trough were performed locally at steady state within 15-25 days after the start of treatment. For each DOAC, the interval of C-trough levels, from the limit of quantification to the highest value, was subdivided into four equal classes, and results were attributed to these classes; the median values of results were also calculated. Thromboembolic complications occurring during 1 year of follow-up were recorded. Results Thromboembolic events (1.8%) occurred in 10 patients who had baseline C-trough levels in the lowest class of drug levels. The incidence of thromboembolic events among patients with DOAC C-trough levels in the lowest level class was 2.4%, and that in the remaining groups was 0%. The patients with thrombotic complications also had a higher mean CHA2 DS2 -VASc score than that of the total patient population: 5.3 (95% confidence interval [CI] 4.3-6.3 versus 3.0 (95% CI 2.9-3.1). Conclusion In this study cohort, thrombotic complications occurred only in DOAC-treated AF patients who had very low C-trough levels, with a relatively high CHA2 DS2 -VASc score. Larger studies are warranted to confirm these preliminary observations.

Lupus-anticoagulant testing at NOAC trough levels

Non-vitamin K antagonist oral anticoagulants (NOAC), including rivaroxaban, apixaban or dabigatran, regularly show relevant effects on coagulation tests, making the interpretation of results difficult. The aim of this study was to evaluate possible interferences of NOACs in trough level concentrations in lupus anticoagulant (LA) testing. Citrate plasma specimens of 30 healthy volunteers were spiked with rivaroxaban, apixaban or dabigatran in four plasma concentration levels at or below trough NOAC levels. The NOAC concentration was measured using dedicated surrogate concentration tests and a stepwise diagnostic procedure for LA-testing was applied using screening, mixing and confirmatory testing. Results were compared to NOAC-free specimens. Starting with a plasma concentration of 12.5 ng/ml, dabigatran-spiked specimens showed significant prolongations in the lupus anticoagulant-sensitive activated partial thromboplastin time (aPTT-LA) as well as in the Dilute Russell viper venom time (dRVVT), leading to 43.3% false positives in confirmatory testing in the dRVVT. In contrast, rivaroxaban, beginning with 7.5 ng/ml, exclusively affected dRVVT-based tests. In confirmatory tests, 30.0% of rivaroxaban-spiked specimens showed false positive results. Starting with 18.75 ng/ml apixaban, a significant prolongation of the dRVVT and up to 20.7% false positives in confirmatory tests were found. In contrast to other NOACs tested, apixaban did not present with a dose-dependent increase of the dRVVT ratio. In conclusion, the rate of false positive results in LA-testing is unacceptably high at expected trough levels of NOACs. Even at plasma concentrations below the LLOQ of commercially available surrogate tests, LA testing is best avoided in patients with NOAC therapy.

Evaluation of activated charcoal and lipid emulsion treatment in model of acute rivaroxaban toxicity

AIM

Reducing or reversing the toxicity effects of new oral anticoagulants is an important question.The purpose of the present study is to evaluate the effect of lipid emulsion (LE) and Activated Charcoal (AC) therapy on the intoxication of rivaroxaban, on mice.

METHODS

Adult male Balb/c mice weighing approximately 30g were used in the study. Seven groups were assigned, with six mice in each group. Groups were defined; given only rivaroxaban, given only LE, given only AC, after the administration of rivaroxaban LE applied group in the 1st hour, after the administration of rivaroxaban LE applied group in the 3rd hour, after the administration of rivaroxaban AC applied group in the1st hour, after the administration of rivaroxaban AC applied group in the 1st hour and LE applied group in the 3rd hour. PT and Anti-Factor Xa activity were measured in all blood samples from subjects.

RESULTS

A statistically significant difference was found when all groups were compared in terms of mean PT values and Anti-FactorXa values. However, no statistically significant difference was found in the mean PT and Anti-FactorXa values when only rivaroxaban administrated group and after the administration of rivaroxaban LE and/or AC applied groups were compared one to one. No deaths occurred in groups during the observation.

CONCLUSION

Although the administration of either AC or LE alone or in combination resulted in a decrease in the mean values of PT and anti-Factor Xa, in case of rivaroxaban toxicity, but one-to-one comparison of the groups was not statistically significant.

Atherothrombosis and Thromboembolism: Position Paper from the Second Maastricht Consensus Conference on Thrombosis

Atherothrombosis is a leading cause of cardiovascular mortality and long-term morbidity. Platelets and coagulation proteases, interacting with circulating cells and in different vascular beds, modify several complex pathologies including atherosclerosis. In the second Maastricht Consensus Conference on Thrombosis, this theme was addressed by diverse scientists from bench to bedside. All presentations were discussed with audience members and the results of these discussions were incorporated in the final document that presents a state-of-the-art reflection of expert opinions and consensus recommendations regarding the following five topics: 1. Risk factors, biomarkers and plaque instability: In atherothrombosis research, more focus on the contribution of specific risk factors like ectopic fat needs to be considered; definitions of atherothrombosis are important distinguishing different phases of disease, including plaque (in)stability; proteomic and metabolomics data are to be added to genetic information. 2. Circulating cells including platelets and atherothrombosis: Mechanisms of leukocyte and macrophage plasticity, migration, and transformation in murine atherosclerosis need to be considered; disease mechanism-based biomarkers need to be identified; experimental systems are needed that incorporate whole-blood flow to understand how red blood cells influence thrombus formation and stability; knowledge on platelet heterogeneity and priming conditions needs to be translated toward the in vivo situation. 3. Coagulation proteases, fibrin(ogen) and thrombus formation: The role of factor (F) XI in thrombosis including the lower margins of this factor related to safe and effective antithrombotic therapy needs to be established; FXI is a key regulator in linking platelets, thrombin generation, and inflammatory mechanisms in a renin-angiotensin dependent manner; however, the impact on thrombin-dependent PAR signaling needs further study; the fundamental mechanisms in FXIII biology and biochemistry and its impact on thrombus biophysical characteristics need to be explored; the interactions of red cells and fibrin formation and its consequences for thrombus formation and lysis need to be addressed. Platelet-fibrin interactions are pivotal determinants of clot formation and stability with potential therapeutic consequences. 4. Preventive and acute treatment of atherothrombosis and arterial embolism; novel ways and tailoring? The role of protease-activated receptor (PAR)-4 vis à vis PAR-1 as target for antithrombotic therapy merits study; ongoing trials on platelet function test-based antiplatelet therapy adjustment support development of practically feasible tests; risk scores for patients with atrial fibrillation need refinement, taking new biomarkers including coagulation into account; risk scores that consider organ system differences in bleeding may have added value; all forms of oral anticoagulant treatment require better organization, including education and emergency access; laboratory testing still needs rapidly available sensitive tests with short turnaround time. 5. Pleiotropy of coagulation proteases, thrombus resolution and ischaemia-reperfusion: Biobanks specifically for thrombus storage and analysis are needed; further studies on novel modified activated protein C-based agents are required including its cytoprotective properties; new avenues for optimizing treatment of patients with ischaemic stroke are needed, also including novel agents that modify fibrinolytic activity (aimed at plasminogen activator inhibitor-1 and thrombin activatable fibrinolysis inhibitor.

Cholestatic liver injury as a side-effect of dabigatran and the use of coagulation tests in dabigatran intoxication and after reversal by idarucizumab in bleeding and sepsis

Idarucizumab, an antidote specific for dabigatran, became available recently. Dabigatran is not associated with increased risk of hepatotoxicity in comparison with warfarin, but it is seen as a rare side-effect. Cases of cholestatic liver injury due to dabigatran have not been reported previously. We present a case of severe gastro-intestinal bleeding with underlying dabigatran intoxication in a patient with renal failure and the effect of reversal of dabigatran using idaruzicumab on coagulation assays. International normalized ratio (INR) and activated partial thromboplastin time (APTT) results were elevated in a setting of sepsis, possibly due to liver failure. INR and APTT can be elevated if sepsis is complicated by disseminated intravascular coagulation (DIC) or liver failure, making it challenging to determine dabigatrans contribution to their prolongation. A rebound effect after administration of idarucizumab and slow elimination of dabigatran due to reduced kidney function could be detected using the Hemoclot^® diluted thrombin time (dTT) in this situation, in contrast to with non-dilutional assays. Before admission, cholestatic liver injury started shortly after initiation of dabigatran etexilate therapy. As no other cause was found, this liver injury was likely to be drug-induced. Bleeding cessated promptly after administration of idarucizumab in dabigatran intoxication. In conclusion, the anticoagulant effect of dabigatran can be measured by Hemoclot^® dTT in sepsis and cholestatic liver injury was seen as a possible rare side-effect of dabigatran treatment.

Comparison of different laboratory tests in the evaluation of hemorrhagic risk of patients using rivaroxaban in the critical care setting: diagnostic accuracy study

Background

Rivaroxaban is a direct oral anticoagulant designed to dispense with the necessity of laboratory monitoring. However, monitoring rivaroxaban levels is necessary in certain clinical conditions, especially in the critical care setting.

Methods

This is a diagnostic accuracy study evaluating sensitivity and specificity of prothrombin time (PT), activated partial thromboplastin time (aPTT), and Dilute Russell viper venom time (dRVVT), to evaluate the hemorrhagic risk in patients taking rivaroxaban. The study used a convenience sample of 40 clinically stable patients using rivaroxaban to treat deep vein thrombosis or atrial fibrillation admitted in a private hospital in Brazil, compared to a group of 60 healthy controls. The samples from patients were collected two hours after the use of the medication (peak) and two hours before the next dose (trough).

Results

The correlation with the plasmatic concentration measured by anti-FXa assay was higher for PT and dRVVTS. The PT and aPTT tests presented higher specificity, while dRVVT was 100% sensible.

Conclusions

There was a strong correlation between the tests and the plasma concentration of the drug. Additionally, our results demonstrated the potential use of dRVVT as a screening test in the emergency room and the need of a second test to improve specificity.

Non-vitamin-K oral anticoagulants and laboratory testing: now and in the future: Views from a workshop at the European Medicines Agency (EMA)

In contrast to vitamin K antagonists, no routine coagulation monitoring is required in patients taking non-vitamin-K oral anticoagulants (NOACs). However, dosing must take into account factors such as patient age, renal function, and accompanying haemorrhagic risk. There has been considerable debate about when laboratory measurement might be appropriate and which tests should be used. A workshop at the European Medicines Agency recently discussed the evidence about laboratory measurement from formal studies, clinical experience, and the multiple perspectives on NOAC treatment, and considered how our knowledge might be further enhanced.

Estimation of Rivaroxaban Plasma Concentrations in the Perioperative Setting in Patients With or Without Heparin Bridging

INTRODUCTION

Estimation of residual rivaroxaban plasma concentrations may be requested before invasive procedures and some patients at high thromboembolic risk will have a bridging therapy with heparins when rivaroxaban is interrupted.

OBJECTIVE

The objective of this study was to assess the performance of the STA-Liquid Anti-Xa assay (STA LAX) and the low and normal procedures of the Biophen Direct Factor Xa Inhibitors (DiXaI) assay, in patients with and without bridging with low-molecular-weight heparins (LMWHs).

MATERIALS AND METHODS

Seventy-nine blood samples were collected from 77 patients on rivaroxaban at C_TROUGH or before an invasive procedure. Rivaroxaban plasma concentrations were estimated using Biophen DiXaI, Biophen DiXaI LOW, and STA LAX and compared to liquid chromatography coupled with mass spectrometry (LC-MS/MS) measurements. Stratifications were performed according to heparin bridging.

RESULTS

The Biophen DiXaI LOW and STA LAX showed better correlation with LC-MS/MS measurements than Biophen DiXaI in patients not bridged with LMWH (R: 0.97, 0.96, and 0.91, respectively). However, the performance of Biophen DiXaI LOW and STA LAX decreased when residual LMWH activity was present (R: 0.18 and 0.19 respectively) demonstrating that these tests are not specific to rivaroxaban.

CONCLUSION

In patients not bridged with LMWH, we suggest to use the Biophen DiXaI LOW and STA LAX for the estimation of rivaroxaban concentrations <50 ng/mL. These results should be confirmed on a larger cohort of patients. Patients bridged with LMWH have inaccurate estimates of low levels of rivaroxaban and the 3 assays studied should not be used to estimate if it is safe to perform a procedure.

Poor comparability of coagulation screening test with specific measurement in patients receiving direct oral anticoagulants: results from a multicenter/multiplatform study

Essentials Prothrombin and partial thromboplastin time (PT/PTT) measure direct oral anticoagulants (DOACs). PT, PTT and specific tests for DOACs were performed on patients treated for atrial fibrillation. Normal PT/PTT don't exclude DOAC activity and their prolongation doesn't confirm DOAC action. The use of PT or PTT to evaluate DOAC activity could cause dangerous misinterpretations.

SUMMARY

Background Prothrombin time (PT) and activated partial thromboplastin time (APTT) have been proposed to measure the effect of oral anti-activated factor X (FXa) or anti-activated FII drugs, respectively. Aims To evaluate the relationships and responsiveness of PT and APTT versus direct oral anticoagulant (DOAC) concentrations measured with specific coagulation tests performed with different platforms in four Italian anticoagulation clinics. Methods Six hundred and thirty-five patients with atrial fibrillation participated in the study: 240 were receiving dabigatran, 264 were receiving rivaroxaban, and 131 were receiving apixaban. Blood was taken at trough and peak within the first month (15-25 days) of treatment. PT, APTT, diluted thrombin time (dTT) calibrated for dabigatran and anti-FXa calibrated for rivaroxaban or apixaban were determined. Results For dabigatran, the correlation between APTT and dTT ranged from r = 0.80 to r = 0.62. For rivaroxaban, the correlation between the anti-FXa assay and PT ranged from r = 0.91 to r = 0.73. For apixaban, the correlation between the anti-FXa assay and PT was lower than for the two other drugs (r = 0.81 to r = 0.54). Despite the above significant correlations, the responsiveness of PT or APTT was relatively poor. A discrepancy between global testing and DOAC plasma concentrations was shown in a considerable proportion of patients, depending on the platform and drug, with values ranging from 6% to 62%. Conclusions Overall, poor responsiveness of the screening tests to DOAC concentrations was observed. PT and APTT normal values cannot exclude DOAC anticoagulant activity, and PT or APTT prolongation is not always associated with DOAC anticoagulant effect as determined with specific tests.

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

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

Reversal agents of non-vitamin K dependent anticoagulants: a rapid review of the changing horizon

The newer non-vitamin K dependent anticoagulants (NOACs) have provided a new tool in the armamentarium of physicians treating nonvalvular atrial fibrillation and thromboembolism. Slowly, but steadily, there has been an increased preference of NOACs over vitamin K antagonists. However, the major limiting factor and the concern that precluded their use was lack of reversal in emergent situations. With the advent of reversal agents such as idarucizumab, andexanet alfa and PER977, this gap is also being filled. This will further increase the spectrum of usage of NOACs. In this review we present the detailed information on the completed trials on the reversal agents, the ongoinng trials, and their site of action. The reversal agent idarucizumab is FDA approved and readily available. The others are in clinical trials and are soon expected to be available in clinical practice.

An update on laboratory measurements of Dabigatran: Smart specific and calibrated dedicated assays for measuring anti-IIa activity in plasma

Use of Direct Oral Anticoagulants (DOACs) is continuously increasing for clinical application. The first product released was Dabigatran, which was proposed for many preventive and curative applications, especially for prevention of stroke in patients with non-valvular atrial fibrillation. Although measurement of Dabigatran Anti-IIa activity in plasma is not requested on a routine basis, in some situations its measurement is clinically useful. Especially, before an emergency surgery in treated patients, where its presence at high concentrations, which will expose the patient at an increased bleeding risk, has to be excluded. Hence, smart, specific, rapid and accurate quantitative assays are warranted as an essential required. Hemoclot™ Thrombin Inhibitors and Biophen® DTI were specifically designed for these applications, and can be used on all automated instruments with a standard range protocol for measuring concentrations at peak, or with a low range protocol for testing residual concentrations. Both functional assays have a good correlation with the reference LC-MS/MS method, and concentrations measured are similar. Performances of these assays and interferences of various substances or drugs are discussed. Some differences in variations of clotting times are observed between mechanical or optical clot detection instruments, which could be explained by the fibrin clot structure, altered by direct Factor Xa inhibitors, and more especially Rivaroxaban. Both clotting and chromogenic assays offer a safe and accurate quantitative measurement of Dabigatran in plasma in all situations where this determination is requested. In short this manuscript provides an in depth update on current opinions on laboratory aspects of measuring Dabigatran concentrations in plasma, when required.

Safety of apixaban for venous thromboembolism prophylaxis: the evidence to date

Apixaban, a direct orally active anticoagulant (selective, direct factor Xa inhibitor) is approved for (primary) prevention of venous thromboembolism (VTE) in patients undergoing elective total-hip or total-knee arthroplasty, for acute treatment/prevention of recurrent events in patients with VTE, and extended prophylaxis in patients with a history of VTE. Another approved use is prevention of stroke and systemic embolism in patients with nonvalvular atrial fibrillation. The present overview focuses on the safety of apixaban specifically in the VTE setting. Apixaban displays favorable pharmacokinetic properties: simple twice-daily dosing, low inter- and intrasubject variability, dose and time linearity, and multiple elimination pathways not critically dependent on either renal or metabolic mechanisms. An extensive nonclinical program and the overall clinical development program (all approved and tested indications) provided no signal that would indicate any particular specific safety concern related to apixaban apart from the increased risk of bleeding. With regard to the approved VTE indications, safety (and efficacy) was assessed in five large pivotal Phase III trials. In comparison to currently recommended standard treatments, apixaban shows superior efficacy, while at the same time no excess risk of bleeding in patients undergoing total-hip or total-knee arthroplasty. In treatment of VTE, apixaban shows noninferior efficacy and a reduced risk of bleeding, whereas in extended prophylaxis it reduced the risk of VTE/VTE-related deaths, with no increased risk of relevant bleedings in comparison to placebo. Documented clinical experience with apixaban in daily practice is currently sparse. However, its use is progressively increasing, and there has been no signal so far that would materially change the perception of its safety profile as defined in the premarketing trials.

Monitoring anticoagulant therapy with new oral agents

Thromboembolic disease is a major leading cause of mortality and morbidity in industrialized countries. Currently, the management of these patients is challenging due to the availability of new drugs with proven efficacy and security compared to traditional oral vitamin K antagonists. These compounds are characterized by a predictable pharmacokinetic profile for which blood monitoring is not routinely needed. Nevertheless, some data have suggested inter-patient variability in the anticoagulant effect of these drugs, raising concerns about their effectiveness and safety. Although mass-spectrometry is the gold standard to determine drug plasma concentrations, this method is not widely available in every-day practice and some coagulation assays are commonly used to determine the anticoagulant effect of these drugs. The present review aims to summarize the current knowledge regarding the clinical question of how and when to monitor patients with new anticoagulant oral agents.