Measurement of dabigatran and rivaroxaban in primary prevention of venous thromboembolism in 106 patients, who have undergone major orthopedic surgery: an observational study

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.

The Influence of ABCB1 (rs1045642 and rs4148738) Gene Polymorphisms on Rivaroxaban Pharmacokinetics in Patients Aged 80 Years and Older with Nonvalvular Atrial Fibrillation

INTRODUCTION

ABCB1 gene polymorphisms are associated with rivaroxaban distribution changes and adverse reactions but the data are controversial.

AIM

To evaluate the influence of ABCB1 (rs1045642 and rs4148738) gene polymorphisms on rivaroxaban pharmacokinetics in patients aged 80 years and older with nonvalvular atrial fibrillation (NAF).

METHODS

128 patients aged 80 years and older (median [Me] age 87.5 [83.0-90.0] years) with NAF were included. We performed ABCB1 (rs1045642 and rs4148738) genotyping, measured the trough steady-state plasma concentration (C_min,ss) of rivaroxaban and prothrombin time (PT) and analyzed prior medical records for clinically relevant non-major bleeding (CRNMB).

RESULTS

CC genotype carriers had no differences in C_min,ss (p > 0.05) compared with the CT and TT rs1045642 and rs4148738 genotypes carriers. CC genotype carriers had no differences in PT (p > 0.05) compared with the CT rs1045642 and rs4148738 and TT rs4148738 genotypes carriers. In the TT genotype PT levels were higher than in the CC rs1045642 genotype: Me 14.2 [13.0-16.1] sec vs 13.3 [12.4-14.5] sec (p = 0.049). Incidence of CRNMB was higher in patients with the TT genotype compared with the CC rs1045642 (29.3% vs 4.5%, p = 0.021) and rs4148738 (39.3% vs 8.1%, p = 0.008) and the CT genotype rs4148738 (39.3% vs 14.3%, p = 0.002).

CONCLUSION

ABCB1 (rs1045642 and rs4148738) polymorphisms didn't influence rivaroxaban pharmacokinetics in patients aged 80 years and older with NAF. TT carriers developed CRNMB more frequently compared with the CC rs1045642 and the CC and CT rs4148738 genotypes. The haplotype TT-TT haplotype was associated with a higher frequency of CRNMB.

A retrospective study of indications and consequences of monitoring direct oral anticoagulant plasma concentrations on patient care in a university hospital: The Retro-AOD study

INTRODUCTION

The use of direct oral anticoagulants (DOAC) is increasing. Specific concentrations are available and have been proven to be reliable and reproducible in optimising patient care. This retrospective, monocentric study aimed to describe the indications and consequences of monitoring DOAC plasma levels on patient care.

MATERIALS AND METHODS

We collected data of patients hospitalised at the Bordeaux University Hospital between January 2017 and December 2018. These included demographics, indications, type, dose of DOAC, standard coagulation tests, creatinine clearance and DOAC plasma concentration using specifically calibrated rivaroxaban and apixaban anti-Xa and dabigatran anti-IIa assays. The date of last DOAC intake, the time between intake and plasma level measurement were also collected and analysed.

RESULTS

A total of 2197 DOAC assays in 1488 patients were obtained in various clinical situations: urgent or elective procedures, context of acute renal failure, suspicion or occurrence of ischemic strokes, intra-cranial and other bleeding sites. Interpretation of these assays led physicians to maintain, postpone or cancel invasive and high haemorrhagic risk procedures in 757, 261 and 56 cases respectively. The remaining 1123 assays were associated with no significant modification of patient care. DOAC plasma concentration was ≤30 ng ml^-1 (sensitivity 85.4%, specificity 73.6%, positive predictive value 71.1%, negative predictive value 86.7%, AUC 0.81) after a last intake of at least 2 days.

CONCLUSIONS

Our study is, to date, the largest report of real-life measurement of specific DOAC plasma level at a single institution. Patient care was not modified in more than half of the assays.

Current use of rivaroxaban in elderly patients with venous thromboembolism (VTE)

Venous thromboembolism (VTE), which is characterized by pulmonary embolism and deep vein thrombosis, has become a serious public concern. Notably, over half of the patients with VTE are over 70 years of age, but elderly patients are at high risk of anti-coagulation and bleeding, which increase with age. Moreover, risk factors and frailty also show a difference between elderly patients and ordinary patients diagnosed with VTE. Rivaroxaban is a direct inhibitor of activated factor Xa and has the advantage of predictable pharmacodynamics and pharmacokinetics, no coagulation monitoring, and few drug interactions. As a first-line therapy for VTE, this drug is more advantageous than traditional therapy and exhibits good efficacy and safety for ordinary patients. However, the effectiveness and safety of rivaroxaban in elderly patients have not been fully elucidated. This article reviewed the use of rivaroxaban in elderly patients, including drug interactions, monitoring, reversal agents of rivaroxaban, and the use of small dosages of rivaroxaban in elderly patients.

Therapeutic monitoring of rivaroxaban in dogs using thromboelastography and prothrombin time

BACKGROUND

The chromogenic anti-Xa assay, the gold standard for monitoring the anti-Xa effect of rivaroxaban, is not available as a cage-side diagnostic test for use in a clinical setting.

HYPOTHESIS/OBJECTIVES

To evaluate clinical modalities for measuring the anticoagulant effects of rivaroxaban using a point-of-care prothrombin time (PT) and thromboelastography (TEG).

ANIMALS

Six healthy Beagle dogs.

METHODS

Prospective, experimental study. Four different doses of rivaroxaban (0.5, 1, 2, and 4 mg/kg) were administered PO to dogs. Single PO and 3 consecutive dosing regimens also were assessed. Plasma rivaroxaban concentration was determined using a chromogenic anti-Xa assay, point-of-care PT, and TEG analysis with 4 activators (RapidTEG, 1 : 100 tissue factor [TF100], 1 : 3700 tissue factor [TF3700], and kaolin), and results were compared. Spearman correlation coefficients were calculated between ratios (peak to baseline PT; peak reaction time [R] of TEG to baseline [R] of TEG) and anti-Xa concentration.

RESULTS

Anti-Xa concentration had a significant correlation with point-of-care PT (R = 0.82, P < .001) and RapidTEG-TEG, TF100-TEG, and TF3700-TEG (R = 0.76, P < .001; R = 0.82, P < .001; and R = 0.83, P < .001, respectively).

CONCLUSIONS AND CLINICAL IMPORTANCE

Overall, a 1.5-1.9 × delay in PT and R values of TEG 3 hours after rivaroxaban administration is required to achieve therapeutic anti-Xa concentrations of rivaroxaban in canine plasma. The R values of TEG, specifically using tissue factors (RapidTEG, TF100, TF3700) and point-of-care PT for rivaroxaban can be used practically for therapeutic monitoring of rivaroxaban in dogs.

Cardiovascular Disease and HIV: Pathophysiology, Treatment Considerations, and Nursing Implications

HIV infection has progressed from an acute, terminal disease to a chronic illness with cardiovascular disease as the leading cause of death among persons living with HIV. As persons living with HIV infection continue to become older, traditional risk factors for atherosclerosis compounded by the pathophysiological effects of HIV infection and antiretroviral therapy markedly increase the risk for cardiovascular disease. Further, persons living with HIV are also at high risk for cardiomyopathy. Critical care nurses must recognize the risk factors for cardiovascular disease and the pathophysiology and complex treatment options in order to manage care of these patients and facilitate multidisciplinary collaboration. Two case studies are used to highlight the treatment options and nursing considerations associated with cardiovascular disease among persons living with HIV.

Influence of dabigatran and rivaroxaban on routine coagulation assays

The Belgian national External Quality Assessment Scheme performed a nationwide survey using lyophilised plasma samples spiked with dabigatran or rivaroxaban to demonstrate to the Belgian clinical laboratories how these drugs affect their routine coagulation assays prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen and antithrombin. Virtually all Belgian laboratories performing routine coagulation testing (189/192) participated in the survey. Both, dabigatran and rivaroxaban significantly prolonged the PT and aPTT in a concentration- and reagent-dependent manner. PT reagents were more influenced by rivaroxaban than by dabigatran and aPTT reagents more influenced by dabigatran than by rivaroxaban. Among PT reagents, Neoplastin R® was the most sensitive to rivaroxaban and Innovin ® and Thromborel S® the least sensitive. Converting PT results to INR only increased the variability between reagents. Among aPTT reagents, Actin FSL® was the least sensitive to dabigatran while the other aPTT reagents showed slightly higher sensitivities. The presence of dabigatran led to falsely reduced fibrinogen concentrations when measured with a low thrombin concentration reagent. The presence of dabigatran caused an overestimation of the antithrombin level when measured with a thrombin-based activity assay and the presence of rivaroxaban an overestimation of the antithrombin level when measured with a FXa-based assay. Instrument-related differences were found for all tested parameters. In conclusion, this paper provides detailed information on the effect of dabigatran and rivaroxaban on routine coagulation assays as performed with a large number of reagent/instrument combinations.

Interindividual variability in dabigatran and rivaroxaban exposure: contribution of ABCB1 genetic polymorphisms and interaction with clarithromycin

Essentials Rivaroxaban and dabigatran are substrates of the P-glycoprotein (P-gp) encoded by the ABCB1 gene. We tested the effect of ABCB1 polymorphisms and of a P-gp inhibitor on both drugs' pharmacokinetics. The ABCB1 genotype was not a clinically relevant determinant of both drugs' pharmacokinetics. Administration of P-gp inhibitors with dabigatran or rivaroxaban should be exercised with caution.

SUMMARY

Background The direct oral anticoagulants (DOACs) dabigatran and rivaroxaban are both substrates of the P-glycoprotein (P-gp) transporter, encoded by the ABCB1 gene. Rivaroxaban is metabolized by cytochrome P450 A4 (CYP3A4). Interindividual variability in DOAC exposure and frequent P-gp-associated drug-drug interactions have been described in patients. Objective To assess the influence of ABCB1 polymorphisms on the pharmacokinetics of dabigatran and rivaroxaban, associated or not with clarithromycin, a P-gp and CYP3A4 inhibitor. Methods Sixty healthy male volunteers, selected according to ABCB1 genotype (20 homozygous mutated, 20 heterozygous mutated, and 20 wild-type for haplotype 2677-3435), were included in this randomized, two-center, crossover study. All received sequentially a single dose of dabigatran etexilate (300 mg) and rivaroxaban (40 mg) associated or not with clarithromycin. Peak plasma concentration and area under the curve (AUC) were compared across the three ABCB1 genotypes. The effect of clarithromycin on dabigatran or rivaroxaban pharmacokinetics was assessed. Results Interindividual coefficients of variation for AUC were 77% for dabigatran and 51% for rivaroxaban. ABCB1 genotype did not significantly affect drug pharmacokinetics: AUC ratios between mutant-allele carriers and wild-type volunteers were 1.27 (95% confidence interval [CI] 0.84-1.92) and 1.20 (95% CI 0.96-1.51) for dabigatran and rivaroxaban, respectively. Clarithromycin coadministration led to a two-fold increase in both drugs' AUC, irrespective of ABCB1 genotype: ratios of geometric means were 2.0 (95% CI 1.15-3.60) and 1.94 (95% CI 1.42-2.63) for dabigatran and rivaroxaban, respectively. Conclusions ABCB1 genotype is not a significant determinant of interindividual variability in dabigatran and rivaroxaban pharmacokinetics. The levels of one drug did not predict the levels of the other. Coadministration of a P-gp/CYP3A4 inhibitor with dabigatran or rivaroxaban may warrant caution in patients at risk of overexposure.

Laboratory determination of old and new targeted anticoagulant agents for prevention of bleeding and thrombotic events in cancer patients

A two-fold prolongation of activated partial thromboplastin time (APTT) is established as therapeutic range for therapy with unfractionated heparin, hirudin and argatroban. The international normalized ratio (INR) of 2 to 3 is required to maintain anticoagulation in the therapeutic range of vitamin K antagonists. The therapeutic range of anti-factor Xa activity during therapy with low-molecular weight heparins and danaparoid are less well and of direct oral anticoagulants (DOAC) poorly defined. The relation of aPTT and INR values to thrombotic and bleeding events are well established despite a large variation of values in affected patients. The relation of coagulation values of the other anticoagulants to clinical events is open. The value of determination in cancer patients is higher because of the increased risk for thrombotic and bleeding events of this patient group. Several activities are currently undertaken to certify methods for in vitro diagnostic testing for DAOCs.

Sensitivity of routine coagulation assays to direct oral anticoagulants: patient samples versus commercial drug-specific calibrators

Most studies on the sensitivities of coagulation assays to direct oral anticoagulants (DOACs) are based on normal plasma spiked with anticoagulant in the laboratory. Recent studies have shown that reagent sensitivity varies significantly depending on whether spiked or patient samples are used. The aim of this study was to compare the sensitivities of routine coagulation assays in patient samples and commercial drug specific calibrators using commonly used activated partial thromboplastin time (APTT) and prothrombin time (PT) reagents (i.e., Actin FS and Neoplastine CI Plus for APTT and PT, respectively) in Australian laboratories. Samples collected at Pathology North Hunter (PN-H) for dabigatran (n=39), rivaroxaban, (n=56) or apixaban levels (n=22) between February 2013 and November 2015 were analysed and compared to two different commercial drug specific calibrators from different manufacturers for each DOAC. Our results show that dabigatran (Hyphen and Technoclone) and rivaroxaban (Stago) calibrators tend to overestimate the APTT but are similar to patient samples for PT. A cut-off DOAC level of 50 ng/mL based on results from patient samples within the laboratory can be used as the lower limit which will result in prolongation of APTT for dabigatran (sensitivity 96%, n=25) and PT for rivaroxaban (sensitivity 97%, n=29), respectively. Individual laboratories should be familiar with the sensitivity of their coagulation reagents to different DOACs including differences between patient samples versus different commercial drug specific calibrators.

Measurement of Non-Vitamin K Antagonist Oral Anticoagulants in Patient Plasma Using Heptest-STAT Coagulation Method

BACKGROUND

Non-vitamin K antagonist oral anticoagulants (NOACs) are approved for several indications for prophylaxis of thromboembolism at fixed oral doses. The analysis of NOAC activity/concentration may be required in special patient populations. Heptest coagulation assay determines both factor Xa and thrombin inhibitors. The objective of investigations is to analyze the effects of both groups of NOACs on this assay.

METHODS

The performance of a modified Heptest-STAT clotting assay was compared with specific chromogenic substrate assays for factor Xa (Coamatic, HemosIL) and thrombin (direct thrombin inhibitor assay and S2238 chromogenic assays) for the determination of rivaroxaban, apixaban, and dabigatran in plasma from patients on treatment.

RESULTS

For rivaroxaban (n = 74), the concentrations (mean and SD) of Heptest-STAT versus Coamatic and HemosIL assays were 179.3 ± 85.8 ng/mL versus 199.3 ± 105.7 ng/mL and 212.4 ± 115.9 ng/mL (P < 0.0001), and for apixaban (n = 26) 232.8 ± 10.0 ng/mL versus 178.4 ± 64.4 ng/mL (P < 0.0001) and 182.1 ± 73.1 ng/mL (P = 0.0002). For dabigatran (n = 74), the values of Heptest-STAT were 92.3 ± 65.0 ng/mL versus 124.3 ± 85.6 ng/mL (direct thrombin inhibitor assay, P < 0.0001) and 107.5 ± 59.7 ng/mL (S2238 assay, P = 0.0015), respectively. The values of the intraclass coefficient of correlation ranged from 0.64 to 0.91 (Bland-Altman analysis).

CONCLUSIONS

The objective of the study was achieved by demonstrating a high correlation of the Heptest-STAT coagulation assay with chromogenic assays for factor Xa inhibiting NOACs and acceptably good correlation with thrombin inhibiting NOACs in plasma samples of patients on treatment.

The laboratory's 2015 perspective on direct oral anticoagulant testing

The introduction of direct oral anticoagulant (DOAC) therapy into clinical use in the past 5 years has had significant impact on the clinical laboratory. Clinicians' desire to determine plasma drug presence or measure drug concentration, and more recent observations regarding the limitations and utility of coagulation testing in the setting of DOAC treatment, suggest that early published recommendations regarding laboratory testing should be reassessed. These initial recommendations, furthermore, were often based on drug-spiked plasma studies, rather than samples from patients receiving DOAC therapy. We have demonstrated that reagent sensitivity varies significantly whether drug-spiked samples or samples from DOAC-treated patients are tested. Data from drug-enriched samples must therefore be interpreted with caution or be used as a guide only. We present laboratory assays that can be used to determine drug presence and to measure drug concentration, and provide recommended testing algorithms. As DOAC therapy may significantly impact on specialty coagulation assays, we review those tests with the potential to give false-positive and false-negative results.

A New Generation of Antiplatelet, and Anticoagulant Medication and the Implications for the Dental Surgeon

The management of dental patients taking either antiplatelet medication, anticoagulant medication or both has been well established in the previous literature. Recently, new generations of drugs have emerged which are becoming increasingly common, including direct thrombin inhibitors, factor X inhibitors and a new class of oral thienopyridines. The implications of these drugs for the dental surgeon are not yet fully known. Awareness remains low and there is very little information available within the literature on safe use during surgery. This review paper aims to provide some guidance for dental practitioners performing invasive procedures. CPD/CLINICAL RELEVANCE: A new generation of anticoagulant and antiplatelet drugs have serious implications for patients undergoing surgery and their use is increasing.

Evaluation of a Heparin-Calibrated Antifactor Xa Assay for Measuring the Anticoagulant Effect of Oral Direct Xa Inhibitors

The introduction of oral direct anti-Xa anticoagulants apixaban and rivaroxaban has significantly impacted the treatment and prevention of thromboembolic disease. Clinical scenarios exist in which a quantitative assessment for degree of anticoagulation due to these agents would aid management. The purpose of this work was to evaluate the chromogenic antifactor Xa assay calibrated with heparin standards at our institution for assessment of intensity of anticoagulation with rivaroxaban or apixaban in addition to its current use for unfractionated heparin or low-molecular-weight heparin. We also aimed to propose expected steady state peak and trough antifactor Xa activities for these agents based upon dosing regimens approved for nonvalvular atrial fibrillation. Antifactor Xa activity correlated very strongly with apixaban and rivaroxaban concentration in both spiked samples and treated patient plasma samples ( r2 = .99, P < .001). This correlation was observed over a broad range (20-500 ng/mL) of drug concentrations, as sample dilution with pooled normal plasma significantly extended the range of quantitative assessment. Based on drug concentrations previously published in pharmacokinetic studies, the expected steady state peak and trough antifactor Xa activity ranges for apixaban are 1.80 to 2.20 IU/mL and 0.70 to 1.10 IU/mL, respectively. For rivaroxaban, these ranges are 3.80 to 6.20 IU/mL and 0.60 to 1.00 IU/mL, respectively. In conclusion, our findings demonstrate that heparin-calibrated antifactor Xa activity correlates strongly with apixaban and rivaroxaban concentration. The dilution of samples allowed for this correlation to be extended over the majority of on-therapy drug concentrations.

Rivaroxaban and apixaban in orthopaedics: is there a difference in their plasma concentrations and anticoagulant effects?

The aim of this study was to improve knowledge of what happens in the coagulation of orthopaedic patients under rivaroxaban and apixaban, in order to finalize and cross-validate effective measurement methods and to provide arguments for helping to reference one or the other drug in our central pharmacy. One hundred and two patients undergoing total hip or knee replacement were included. Half of them received rivaroxaban and the other half received apixaban. Blood samples (n = 244 with each drug) were taken at Cmax preoperatively and twice a week, apart from the day of the patient's discharge, when Ctrough concentration was targeted. Routine coagulation parameters, and functional and liquid chromatography tandem mass spectrometry assays for measurement of circulating concentrations were studied. The LC-MS/MS assay and the functional assays carried out in patients under routine conditions were highly correlated, apart from low concentrations (<30 ng/ml), which were affected by the variable individual potential to inhibit the exogenous bovine Xa used in the functional assays. After 1 week of treatment, the drugs differed: Cmax and Ctrough were closer when apixaban was taken twice daily (83 ± 39 and 58 ± 17 ng/ml) than with rivaroxaban taken once a day (113 ± 67 and 13 ± 20 ng/ml). Rivaroxaban had a greater influence on routine coagulation tests and reduced the maximum thrombin concentration more efficiently, as assessed by the thrombin generation test. Although rivaroxaban and apixaban present apparently similar constant rates, they exhibit significant differences in their concentrations and anticoagulant effects when studied ex vivo in orthopedic patients.

A Study of the Management of Patients Taking Novel Oral Antiplatelet or Direct Oral Anticoagulant Medication Undergoing Dental Surgery in a Rural Setting

PURPOSE

Novel oral antiplatelet (NOAP) (prasugrel and ticagrelor) and direct oral anticoagulant drugs (DOAC) (dabigatran, rivaroxaban and apixaban) have emerged in the last decade. This study was undertaken to determine current approaches taken to the management of patients taking these agents in dental practice in a remote and rural setting.

METHODS

A small retrospective study was carried out in a small island population that identified patients taking one of the above drugs. All national health service and private dental records were examined to determine the type of treatment carried out and whether drug therapy, treatment plans or actual treatment were modified as a result of NOAP or DOAC therapy. In addition other outcomes such as referral to another service for advice or treatment and any adverse bleeding events were noted.

RESULTS

156 dental encounters for 95 patients taking one of the drugs were identified. Significant events were identified in sixteen encounters and the management of patients taking each drug type differed significantly between cases but no patients returned with troublesome post-operative bleeding.

CONCLUSIONS

The approaches taken by dental surgeons in Orkney in the management of the NOAPs and DOACs varied and this is likely to be a reflection of the limited literature available.

Coagulation assessment with the new generation of oral anticoagulants

Long-term oral anticoagulant (OAC) therapy is used for the treatment and prevention of thrombosis and thromboembolism. As OAC use is so widespread, emergency physicians are likely to encounter patients on anticoagulant therapy in the emergency department (ED) on a regular basis, either for the same reasons as the population in general or as a result of the increased bleeding risk that OAC use entails.

The vitamin K antagonist warfarin has been the standard OAC for several decades, but recently, the newer agents dabigatran etexilate, rivaroxaban and apixaban (collectively, novel OACs, non-vitamin K OACs, or simply ‘NOACs’) have become available for long-term use. Protocols for assessing and managing warfarin-treated patients in the ED are well established and include international normalised ratio (INR) testing, which helps guide patient management. However, the INR does not give an accurate evaluation of coagulation status with NOACs, and alternative tests are therefore needed for use in emergency settings. This paper discusses what information the INR provides for a patient taking warfarin and which coagulation tests can guide the physician when treating patients on one of the NOACs, as well as other differences in emergency anticoagulation management.

[Perioperative management of direct oral anticoagulant in emergency surgery and bleeding. Haemostasis monitoring and treatment]

There is an almost unanimous consensus on the management of the direct new oral anticoagulants, dabigatran, rivaroxaban, and apixaban in elective surgery. However, this general consensus does not exist in relation with the direct new oral anticoagulants use in emergency surgery, especially in the bleeding patient. For this reason, a literature review was performed using the MEDLINE-PubMed. An analysis was made of the journal articles, reviews, systematic reviews, and practices guidelines published between 2000 and 2014 using the terms "monitoring" and "reversal". From this review, it was shown that the routine tests of blood coagulation, such as the prothrombin time and activated partial thromboplastin time, have a limited efficacy in the perioperative control of blood coagulation in these patients. There is currently no antidote to reverse the effects of these drugs, although the possibility of using concentrated prothrombin complex and recombinant activated factor vii has been suggested for the urgent reversal of the anticoagulant effect.

Laboratory measurement of the anticoagulant activity of the non-vitamin K oral anticoagulants

BACKGROUND

Non-vitamin K oral anticoagulants (NOACs) do not require routine laboratory monitoring. However, laboratory measurement may be desirable in special situations and populations.

OBJECTIVES

This study's objective was to systematically review and summarize current evidence regarding laboratory measurement of the anticoagulant activity of dabigatran, rivaroxaban, and apixaban.

METHODS

We searched PubMed and Web of Science for studies that reported a relationship between drug levels of dabigatran, rivaroxaban, and apixaban and coagulation assay results. Study quality was evaluated using QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies 2).

RESULTS

We identified 17 eligible studies for dabigatran, 15 for rivaroxaban, and 4 for apixaban. For dabigatran, a normal thrombin time excludes clinically relevant drug concentrations. The activated partial thromboplastin time (APTT) and prothrombin time (PT) are less sensitive and may be normal at trough drug levels. The dilute thrombin time (R(2) = 0.92 to 0.99) and ecarin-based assays (R(2) = 0.92 to 1.00) show excellent linearity across on-therapy drug concentrations and may be used for drug quantification. For rivaroxaban and apixaban, anti-Xa activity is linear (R(2) = 0.89 to 1.00) over a wide range of drug levels and may be used for drug quantification. Undetectable anti-Xa activity likely excludes clinically relevant drug concentrations. The PT is less sensitive (especially for apixaban); a normal PT may not exclude clinically relevant levels. The APTT demonstrates insufficient sensitivity and linearity for quantification.

CONCLUSIONS

Dabigatran, rivaroxaban, and apixaban exhibit variable effects on coagulation assays. Understanding these effects facilitates interpretation of test results in NOAC-treated patients. More information on the relationship between drug levels and clinical outcomes is needed.

What is the effect of rivaroxaban on routine coagulation tests?

A 78-year-old female presents to the emergency department with a traumatic hip fracture. Her past medical history is significant for atrial fibrillation for which she receives rivaroxaban 20 mg daily. Her dose was last taken 12 hours ago. Routine bloodwork conducted in the emergency department shows prothrombin time, international normalized ratio, and activated partial thromboplastin time within the normal range, and estimated glomerular filtration rate of 50 mL/min/1.73 m(2) (normal is >90 mL/min/1.73 m(2)) You are asked by the surgical team to confirm that it is safe to proceed with surgery at this time using neuraxial anesthesia.

The target-specific oral anticoagulants: practical considerations

More than 4 years have passed since the first approval of a target-specific oral anticoagulant (TSOAC) in the United States, and the number of clinicians who have prescribed (or considered prescribing) one or more of these medications is increasing. Although these agents may, in properly selected patients, offer advantages over more traditional therapies, their lack of familiarity can be intimidating. Clinicians who are prescribing the TSOACs face a number of management questions not definitively answered by the registration trials. This chapter reviews some of these situations, including updated information on the periprocedural management of TSOACs and the latest evidence about how to best measure TSOAC effect. The lack of an antidote and other considerations that may be relevant when deciding between newer and more traditional anticoagulant medications are also discussed.

Measurement of rivaroxaban and apixaban in serum samples of patients

BACKGROUND

The determination of rivaroxaban and apixaban from serum samples of patients may be beneficial in specific clinical situations when additional blood sampling for plasma and thus the determination of factor Xa activity is not feasible or results are not plausible.

MATERIALS AND METHODS

The primary aim of this study was to compare the concentrations of rivaroxaban and apixaban in serum with those measured in plasma. Secondary aims were the performance of three different chromogenic methods and concentrations in patients on treatment with rivaroxaban 10 mg od (n = 124) or 20 mg od (n = 94) or apixaban 5 mg bid (n = 52) measured at different time.

RESULTS

Concentrations of rivaroxaban and apixaban in serum were about 20-25% higher compared with plasma samples with a high correlation (r = 0·79775-0·94662) using all assays (all P < 0·0001). The intraclass correlation coefficients were about 0·90 for rivaroxaban and 0·55 for apixaban. Mean rivaroxaban concentrations were higher at 2 and 3 h compared with 1 and 12 h after administration measured from plasma and serum samples (all P-values < 0·05) and were not different between 1 vs. 12 h (plasma and serum).

CONCLUSIONS

The results indicate that rivaroxaban and apixaban concentrations can be determined specifically from serum samples.

Pharmacology and laboratory testing of the oral Xa inhibitors

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

Perioperative management of patients receiving new oral anticoagulants: an international survey

New oral anticoagulants (NOACs) are increasingly replacing standard anticoagulants. These new drugs have been recently introduced in clinical practice, and specific knowledge regarding preoperative interruption, anticoagulation assessment, and reversal therapies is needed. In this article, 3 main areas related to perioperative NOACs management are discussed: (1) physicians' knowledge, (2) current practices, and (3) perspectives to improve management of patients treated with NOACs.

Performance of various laboratory assays in the measurement of dabigatran in patients receiving therapeutic doses: a prospective study based on peak and trough plasma levels

OBJECTIVES

To study dabigatran etexilate, a new oral anticoagulant that functions as a direct thrombin inhibitor.

METHODS

This study evaluates four methods, one of which is performed in three different laboratories, and compares results against dabigatran levels measured by Boehringer-Ingelheim (Ingelheim, Germany) using mass spectrometry.

RESULTS

Although routine monitoring is not required, measurement of plasma concentrations may be necessary in certain clinical situations. Routine coagulation assays such as the prothrombin time, activated partial thromboplastin time, and thrombin time do not reliably determine levels of dabigatran anticoagulation. Alternative assays, when calibrated with a dabigatran standard, such as the modified dilute thrombin time, ecarin clotting time, and ecarin chromogenic assay, may be appropriate, although a comparison of these methods using samples from patients taking dabigatran has not been performed.

CONCLUSIONS

Although results using all methods in this study demonstrate adequate correlation, measured dabigatran levels varied in a statistically significant manner, even when the same method was used by different laboratories. The clinical significance of this variation in dabigatran concentrations is uncertain.

Importance of pharmacokinetic profile and variability as determinants of dose and response to dabigatran, rivaroxaban, and apixaban

Warfarin has been the mainstay oral anticoagulant (OAC) medication prescribed for stroke prevention in atrial fibrillation (AF) patients. However, warfarin therapy is challenging because of marked interindividual variability in dose and response, requiring frequent monitoring and dose titration. These limitations have prompted the clinical development of new OACs (NOACs) that directly target the coagulation cascade with rapid onset/offset of action, lower risk for drug-drug interactions, and more predictable response. Recently, NOACs dabigatran (direct thrombin inhibitor), and rivaroxaban and apixaban (factor Xa [FXa] inhibitors) have gained regulatory approval as alternative therapies to warfarin. Though the anticoagulation efficacy of these NOACs has been characterized, differences in their pharmacokinetic and pharmacodynamic profiles have become a significant consideration in terms of drug selection and dosing. In this review, we outline key pharmacokinetic and pharmacodynamic features of each compound and provide guidance on selection and dosing of the 3 NOACs relative to warfarin when considering OAC therapy for AF patients. Importantly, we show that by better understanding the effect of clinical variables such as age, renal function, dosing interval, and drug metabolism (CYP3A4) and transport (P-glycoprotein), we might be able to better predict the risk for sub- and supratherapeutic anticoagulation response and individualize OAC selection and dosing.

New oral anticoagulants: discussion on monitoring and adherence should start now!

New oral anticoagulants (NOACs) have been introduced to improve anticoagulant therapy worldwide, but safe implementation may require additional measures. First, optimization of dose adjustment based on therapeutic levels of the drug may be more appropriate than fixed dose therapy. The development and implementation in quantitative laboratory assays will enable further dose optimization. Second, non-adherence to medication is a potential threat to the safe use of NOACs. Since cardiovascular medication may not be optimally used in about 50% of patients, procedures to improve adherence are imperative, also for NOAC therapy and in particular in elderly patients.

The role of the laboratory in treatment with new oral anticoagulants

Orally active small molecules that selectively and specifically inhibit coagulation serine proteases have been developed for clinical use. Dabigatran etexilate, rivaroxaban and apixaban are given at fixed doses and do not require monitoring. In most circumstances, these drugs have predictable bioavailability, pharmacokinetic effects, and pharmacodynamic effects. However, there will be clinical circumstances when assessment of the anticoagulant effect of these drugs will be required. The effect of these drugs on laboratory tests has been determined in vitro by spiking normal samples with a known concentration of active compound, or ex vivo by using plasma samples from volunteers and patients. Data on the sensitivity of different reagents are now available, and so guidance as to the effect and interpretation of a test result is now possible. Laboratories should be aware of the sensitivity of their own assays to each drug. This may be achieved by using appropriate calibrated plasma samples.