Measuring the anticoagulant effects of target specific oral anticoagulants-reasons, methods and current limitations

Bioavailability of Orally Administered Drugs After Bariatric Surgery

PURPOSE OF REVIEW

Oral drug absorption after bariatric surgery is likely to be altered, but the impact of different bariatric surgery procedures on individual drugs is not uniform. The aim of this article is to describe factors influencing the bioavailability of orally administered drugs after bariatric surgery and to provide readers with practical recommendations for drug dosing. We also discuss the medications that may be harmful after bariatric surgery.

RECENT FINDINGS

The fundamental factors for enteral drug absorption are the production of gastric acid; the preserved length of the intestine, i.e., the size of the absorption surface and/or the preserved enterohepatic circulation; and the length of common loop where food and drugs are mixed with digestive enzymes and bile acids. Bypassing of metabolizing enzymes or efflux pumps and changes in intestinal motility can also play an important role. Significant changes of drug absorption early after the anatomic alteration may also be gradually ameliorated due to gradual intestinal adaptation. The most affected drugs are those with low or variable bioavailability and those undergoing enterohepatic circulation. Attention should also be paid to oral drug formulations, especially in the early postoperative period, when immediate-release and liquid formulations are preferred. The changes in oral bioavailability are especially clinically meaningful in patients treated with drugs possessing narrow therapeutic index (e.g., oral anticoagulants, levothyroxine, and anticonvulsants) or in acute conditions (e.g., anti-infectives); nevertheless, it may also influence the therapeutic value of chronic therapy (e.g., antidepressants. antihypertensives, antiplatelets, statins, PPIs, contraceptives, and analgesics); therapeutic effect of chronic therapy is further influenced by pharmacokinetic alterations resulting from weight loss. Therapeutic drug monitoring, periodical clinical evaluation, and adequate dose adjustments are necessary. Due to safety reasons, patients should avoid oral bisphosphonates, regular use of non-steroidal anti-inflammatory drugs, and, if possible, corticosteroids after bariatric surgery.

Long-Term Outcomes of Bariatric Surgery in Patients on Chronic Anticoagulation

BACKGROUND

Approximately 3% of patients undergoing metabolic and bariatric surgery (MBS) are receiving chronic anticoagulation therapy (CAT) prior to operation. The management of these patients is complex, as it involves balancing the potential risk of thrombosis against that of bleeding. Our primary objective is to assess the long-term bleeding risk in patients undergoing MBS. We also aim to observe the trends in anticoagulant dosing after MBS.

METHODS

A single-center retrospective review of patients who underwent either primary Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) with preoperative CAT between 2008 and 2022 was performed. Data on baseline demographics, indication for anticoagulation, type of CAT, and dosing were collected. Events of bleeding and the CAT at event were subsequently evaluated.

RESULTS

A total of 132 patients (82 RYGB and 50 SG) initially on CAT were identified, with atrial fibrillation being the most common indication. Incidence of long-term bleeding was significantly higher in the RYGB group (18.3%) compared to the SG group (4%) (p = 0.017) over a total of 5.2 ± 3.8 years. Bleeding marginal ulcer (MU) was the most common cause of bleeding in the RYGB group (13.4%). 84.2% of all bleeding events occurred in patients on chronic Warfarin therapy.

CONCLUSION

Long-term CAT is associated with an increased risk of bleeding in RYGB patients, particularly MU bleeds. Patients on CAT seeking MBS should be counseled regarding this risk and potential implications. Direct-acting oral anticoagulants offer promise as an alternative to Warfarin in these patients; further research is necessary to better understand their safety.

Altered plasma levels of apixaban in major gastrointestinal tract surgery: a case report and review of the literature

Altered direct oral anticoagulant (DOAC) plasma levels can lead either to spontaneous hemorrhagic or thrombotic complications. We describe a case of suspected altered apixaban disposition in a patient with an upper gastrointestinal cancer resection treated with apixaban for non-valvular atrial fibrillation. Diagnosis of ischemic stroke for left hemiparesis was confirmed due to recent emergence of a hypodense area in the posterior capsular nucleus of ischemic reference in a context of binuclear capsular lacunar lesions. Thus, apixaban underexposure was suspected from anamnestic data and oral anticoagulation was switched to parenteral at the next scheduled dose for stroke recurrence. Before switching apixaban pharmacokinetic analysis was performed and unexpectedly showed apixaban plasma overexposure. After 3 days from the switch, the patient experienced spontaneous bleeding complications, for which the risk-benefit profile of continuing anticoagulant treatment for stroke recurrences warranted treatment discontinuation. Unexpected DOAC plasma exposure may present in special patient populations with thrombotic and bleeding complications. Though universally recognized therapeutic ranges have yet to be established for DOACs, periodic drug monitoring may aid in guiding optimization of DOAC therapy and reduce the risk of adverse events in special patient populations.

Direct oral anticoagulants after bariatric surgery-What is the evidence?

BACKGROUND

Obesity is a global epidemic and bariatric surgery is used with increasing frequency to treat its complications. The extent to which bariatric surgery alters the efficacy, safety, and pharmacokinetics of direct oral anticoagulants (DOACs) is unknown.

AIMS

In this review, we summarize the evidence supporting the use of DOACs after bariatric surgery and apply our findings to resolve several clinical cases.

MATERIALS & METHODS

We systematically searched MEDLINE, EMBASE, Cochrane Library, CINAHL and ClinicalTrials.gov from January 1, 2000, to June 15, 2021 for randomized and non-randomized studies evaluating the use of DOACs for any indication after bariatric surgery. Two reviewers independently screened titles, abstracts, and full-text articles. Clinical and pharmacokinetic outcomes were pooled by random-effects meta-analysis with inverse variance weighting. We used the Newcastle-Ottawa scale to assess risk of bias in non-randomized studies and assessed the certainty of evidence with GRADE.

RESULTS

From 2519 records, we included 28 studies (n = 3229 patients): no randomized trials, 7 cohort studies, 6 case series, and 15 case reports. Incidence rates for arterial thromboembolism, venous thromboembolism and major bleeding were: 0.73 (95% confidence interval [CI]: 0.01-5.10), 2.45 (95% CI: 0.40-7.94), and 3.40 (95% CI: 0.80-9.36) events per 100 patient-years, respectively. The pooled proportion of peak direct oral anticoagulant drug levels within the expected range was 58% (95% CI: 39%-74%).

CONCLUSION

There appears be substantial risk of DOAC malabsorption after bariatric surgery that could affect clinical outcomes, however the certainty of evidence was very low.

PROSPERO

CRD42020202636.

Apixaban and rivaroxaban anti-Xa level utilization for guidance of administration of andexanet alfa: a case series

BACKGROUND

Andexanet alfa, a modified recombinant factor Xa (FXa), was FDA approved in 2018 for anticoagulant reversal in patients with life-threatening bleeding associated with FXa inhibitors (FXaI). The ANNEXA-4 investigators administered andexanet alfa to patients within an 18-h from last dose of oral FXaI. In practice, time from last dose is often unknown. Previous studies have shown that clearance of these agents may be impaired by renal and hepatic dysfunction, as well as drug-drug interactions. Decision for use of andexanet alfa is also complicated by its high cost, limited drug availability, and thrombotic risk. This study aimed to describe the utility of anti-Xa DOAC levels as a decision point to administer andexanet alfa.

METHODS

This is a case series of four patients with an anti-Xa DOAC level that received andexanet alfa for oral FXaI reversal in the setting of life-threatening bleeding or prior to procedure.

RESULTS

Four patients were included in the study. Two patients had a known time since last dose of oral FXaI. All patients had a detectable anti-Xa DOAC levels prior to administration of andexanet alfa. Two patients had levels within the peak range, one patient had a level below the peak range, and one patient had a level above the peak range. Andexanet alfa was administered after anti-Xa DOAC level return in all patients.

CONCLUSION

In our case series, obtaining anti-Xa DOAC levels prior to administration of andexanet alfa was achievable and facilitated use of reversal agents in patients with major bleeding or emergent procedural need.

Evaluation of Anti-Xa Apixaban and Rivaroxaban Levels With Respect to Known Doses in Relation to Major Bleeding Events

BACKGROUND

Although not routinely recommended, anti-Xa level monitoring for apixaban or rivaroxaban may be useful in certain clinical scenarios. There are currently no laboratory standards, therapeutic ranges, or proven correlation between anti-Xa levels and clinical outcomes.

OBJECTIVE

This study describes the utilization, application, and association of anti-Xa levels with clinical outcomes in patients receiving apixaban or rivaroxaban.

METHODS

This retrospective, descriptive study included adult inpatients within the Houston Methodist System on apixaban or rivaroxaban with at least one anti-Xa level ordered subsequent to administered doses. The primary endpoint was major bleeding according to International Society on Thrombosis and Haemostasis criteria. Secondary endpoints included reasons for anti-Xa level ordering, anti-Xa levels at different time intervals post-dose, and thrombotic events. Pre-specified subgroup analyses were performed to further evaluate the primary endpoint.

RESULTS

The study population consisted of 169 patients and 234 anti-Xa levels. Twenty-nine levels were obtained in context of major bleeding. The majority of levels were not drawn as peak levels 2-4 hours post-dose, however remained quantifiable above typical observed levels within this timeframe and well beyond 24 hours post-dose. Patient characteristics with major bleeding included elderly age, acute renal impairment, and low body weight. At least 14 unique reasons for anti-Xa level ordering were identified. Twenty-nine levels were associated with thrombotic events.

CONCLUSION

Anti-Xa levels may be useful for assessment of current drug concentrations, immediate safety of therapy, and guidance for possible clinical interventions. Dose titration and reversal therapies based on anti-Xa level results in major bleeding warrant further research.

Outcomes Associated With 4-Factor Prothrombin Complex Concentrate Administration to Reverse Oral Factor Xa Inhibitors in Bleeding Patients

Compared with vitamin K antagonists (VKAs), oral factor Xa inhibitors are associated with at least equivalent efficacy and a lower incidence of major bleeding. Despite this benefit, bleeding remains the most common adverse event. Prior to the approval of andexanet alfa, alternative agents such as 4-factor prothrombin complex concentrate (4F-PCC) were utilized for reversal. This was a retrospective, descriptive study conducted on patients 18 years of age or older who received 4F-PCC for reversal of oral factor Xa inhibitors-associated bleeding. Patients were excluded if they received a VKA or dabigatran in the previous 48 hours. A subgroup analysis comparing 4F-PCC with andexanet alfa was conducted on patients who met the inclusion and exclusion criteria of the ANNEXA-4 trial. The primary end point of this study was to evaluate the incidence of hemostasis and associated dosing strategies in patients receiving 4F-PCC for reversal of oral factor Xa inhibitors-associated bleeding. Thirty-eight patients were included, and 28 patients (74%) achieved hemostasis. The median dose of 4F-PCC was 50 units/kg. In patients who achieved hemostasis, the median dose was 50 units/kg, and in those who failed to reach hemostasis, a median dose of 30 units/kg was seen. Within the subgroup analysis, there was no difference in overall rates of hemostasis between the 4F-PCC and andexanet alfa groups. Remaining a reasonable option to utilize for reversal of oral factor Xa inhibitors is 4F-PCC, especially when andexanet alfa is unavailable, with 50 units/kg appearing to be the most effective dose to achieve hemostasis. Further studies are needed to determine a preferential agent.

Evaluation of characteristics and dosing regimens in patients with new or recurrent thrombosis on apixaban and rivaroxaban

Direct factor Xa inhibitors, such as apixaban and rivaroxaban, are widely used for treatment and prevention of venous thromboembolism; however, recent cases of therapeutic failure have been reported. Potential risk factors associated with therapeutic failure such as dose deviations outside of package labeling recommendations, and the use of direct factor Xa-specific inhibitor levels to guide clinical decision making continue to be areas of further investigation. Our study aimed to describe characteristics and dosing regimens in patients on apixaban or rivaroxaban who experienced a new or recurrent thrombosis. We performed a retrospective chart review on 190 patients on either apixaban or rivaroxaban presenting to our institution with new or breakthrough thromboembolism. Evaluation of prescribed anticoagulation regimens compared to package labeling recommendations, direct factor Xa inhibitor-specific anti-Xa levels, anticoagulation interruptions, use of parenteral bridge anticoagulation, final anticoagulation regimen disposition, and thrombosis-associated mortality were recorded. In patients presenting with breakthrough thromboembolism, 78% were on a regimen that matched package labeling recommendations. Anti-Xa levels were documented in 66 patients, the majority of which fell within institutional expected ranges at time of thrombosis. Therapy interruptions immediately prior to thrombosis were observed in 22% of patients and 21% of those patients received parenteral anticoagulation during interruption. Upon discharge, 46% of patients continued the same anticoagulation regimen with no changes. The mortality rate was 6%. In patients who present with new thromboembolism on apixaban or rivaroxaban, a thorough review of risks and benefits should be conducted to mitigate future risk of recurrent thrombosis.

Bariatric Surgery can Lower the Efficacy of DOACs

A 39-year-old woman who was taking the contraceptive pill was admitted with right leg deep venous thrombosis (DVT). She was started on apixaban tablets, but after 8 days developed proximal progression of the DVT and pulmonary embolism. Her medical history later showed a history of sleeve gastrectomy. The patient responded to a vitamin K antagonist after heparin. The failure of the antithrombotic drug shed light on the efficacy and changed pharmacodynamics of direct oral anticoagulants (DOACs) after bariatric surgery in the absence of commercially available blood monitoring tests.

Real-time detection and differentiation of direct oral anticoagulants (rivaroxaban and dabigatran) using modified thromboelastometric reagents

INTRODUCTION

Timely measurement of direct oral anticoagulants (DOACs) is challenging, though clinically important. We tested the hypotheses, that thromboelastometry is able to detect dabigatran and rivaroxaban and discriminates between dabigatran and rivaroxaban as representatives of the two groups of DOACs.

METHODS AND MATERIALS

We conducted a prospective-observational study: In-vitro dose-effect-curves for rivaroxaban and dabigatran were performed (n = 10). Ex-vivo: Patients with indication of DOAC treatment (stroke; dabigatran/rivaroxaban) were included (n = 21). Blood samples were analyzed before first intake, at first estimated peak level and at 24 h after first but before following intake and 3 h after 24 h-intake. Standard and modified thromboelastometric-assays, using low tissue factor concentrations (TFTEM) or ecarin (ECATEM) were used. Receiver-operating-characteristics-curve-analysis (ROC), regression-analysis and two-way-ANOVA were performed.

RESULTS

In-vitro: TFTEM detected dabigatran and rivaroxaban (ROC_AUC: 0.99; sensitivity/specificity: 100%/98%) but could not discriminate. Dabigatran prolongs CT_ECATEM whereas rivaroxaban did not. Clotting Time (CT)-ratio TFTEM/ECATEM discriminated highly sensitive (100%) and specific (100%) between dabigatran and rivaroxaban even at very low concentrations (ROC_AUC:1.0). CT_ECATEM correlated with dabigatran spiked concentrations (r = 0.9985; p < 0.001) and CT_TFTEM (r = 0.9363; p = 0.006) with rivaroxaban. Similarly results could be demonstrated with patient data: We confirmed the performance for the differentiation of CT-ratio TFTEM/ECATEM (sensitivity 100%/specificity 100%) at any time after first intake of either DOAC.

CONCLUSION

The thromboelastometric tests TFTEM and ECATEM detect and differentiate rivaroxaban and dabigatran. Further investigations evaluate the other DOACs and the differentiation to phenprocoumon. However, results need to be confirmed in a larger study, and especially cut off values for differentiation need to be calculated from a larger sample size.

How I treat cancer-associated thrombosis

Patients with cancer are at an increased risk of symptomatic venous thromboembolism (VTE). In addition, an increasing number of patients with incidental thromboembolic events have been recorded in clinical practice. Therapeutic anticoagulation is crucial to prevent thrombus progression and reduce risk of recurrence; however, this comes at the price of an increased bleeding risk, which necessitates a personalised approach to choose the most appropriate type of therapy. Over the last decade, low-molecular-weight heparin has been the preferred anticoagulant agent for patients with cancer-associated thrombosis due to better efficacy and similar safety profile compared with vitamin K antagonists. While direct oral anticoagulants (DOAC) have emerged as new option for treatment of VTE in a general population, only limited data have been available specifically for patients with cancer until recently. Randomised, controlled trials have now been published, establishing DOAC as an alternative for the treatment of cancer-associated thrombosis. However, the improvement in the therapeutic armamentarium is accompanied by a number of special considerations. For instance, risk of bleeding is elevated in patients with cancer-associated VTE receiving DOAC, especially in certain tumour types (eg, gastrointestinal), and no guidance exists regarding their use in patients with severe thrombocytopaenia. Furthermore, DOAC are prone to certain drug-drug interactions and their effect might be altered due to nausea and vomiting in patients receiving chemotherapy. Here, we provide guidance on how to treat cancer-associated VTE and how new evidence from randomised controlled trials can be implemented in clinical practice. There are still clinical scenarios where robust evidence is lacking and treatment recommendations are based on extrapolations from other populations or expert opinion only. Therefore, additional research in special subpopulations is needed to optimise management of patients in challenging clinical scenarios.

Diagnostic accuracy of thromboelastometry and its correlation with the HPLC-MS/MS quantification test

The aim of the study was to evaluate the diagnostic accuracy of thromboelastometry for assessing rivaroxaban concentrations. The accuracy of thromboelastometry was compared with the high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method, which is the gold standard for drug plasma monitoring (the reference standard). Forty-six clinically stable patients were treated with 10, 15, or 20 mg of rivaroxaban once daily (OD group) or 15 mg twice a day (BID group) (no particular indication for treatment). Patient samples were collected 2 h after the use of the medication (peak) and 2 h before the next dose (trough). The rivaroxaban plasma concentrations were determined via HPLC-MS/MS, and thromboelastometry was performed using a ROTEM® delta analyzer. There were significant prolongations in clotting time (CT) for the 10, 15, and 20 mg of rivaroxaban treatments in the OD groups. In the 15 mg BID group, the responses at the peak and trough times were similar. At the peak times, there was a positive correlation between the plasma concentration of rivaroxaban and CT (Spearman correlation rho=0.788, P<0.001) and clot formation time (rho=0.784, P<0.001), and a negative correlation for alpha angle (rho=−0.771, P<0.001), amplitude after 5 min (rho=−0.763, P<0.001), and amplitude after 10 min (rho=−0.680, P<0.001). The CT presented higher specificity and sensitivity using the cut-off determined by the receiver characteristics curve. ROTEM has potential as screening tool to measure possible bleeding risk associated with rivaroxaban plasma levels.

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.

Unanswered questions and research priorities to optimise stroke prevention in atrial fibrillation with the new oral anticoagulants

This review article discusses the following, as yet unanswered, questions and research priorities to optimise patient management and stroke prevention in atrial fibrillation with the new direct oral anticoagulants (NOACs): 1. In patients prescribed a NOAC, can the anticoagulant effects or plasma concentrations of the NOACs be measured rapidly and reliably and, if so, can “cut-off points” between which anticoagulation is therapeutic (i.e. the “therapeutic range”) be defined? 2. In patients who are taking a NOAC and bleeding (e.g. intracerebral haemorrhage), can the anticoagulant effects of the direct NOACs be reversed rapidly and, if so, can NOAC-associated bleeding and complications be minimised and patient outcome improved? 3. In patients taking a NOAC who experience an acute ischaemic stroke, to what degree of anticoagulation or plasma concentration of NOAC, if any, can thrombolysis be administered safely and effectively? 4. In patients with a recent cardioembolic ischaemic stroke, what is the optimal time to start (or re-start) anticoagulation with a NOAC (or warfarin)? 5. In anticoagulated patients who experience an intracranial haemorrhage, can anticoagulation with a NOAC be re-started safely and effectively, and if so when? 6. Are the NOACs effective and safe in multimorbid geriatric people (who commonly have atrial fibrillation and are at high risk of stroke but also bleeding)? 7. Can dose-adjusted NOAC therapy augment the established safety and efficacy of fixed-dose unmonitored NOAC therapy? 8. Is there a dose or dosing regimen for each NOAC that is as effective and safe as adjusted-dose warfarin for patients with atrial fibrillation who have mechanical prosthetic heart valves? 9. What is the long-term safety of the NOACs?

Oral Anticoagulant Use After Bariatric Surgery: A Literature Review and Clinical Guidance

Bariatric surgery may alter the absorption, distribution, metabolism, or elimination (disposition) of orally administered drugs via changes to the gastrointestinal tract anatomy, body weight, and adipose tissue composition. As some patients who have undergone bariatric surgery will need therapeutic anticoagulation for various indications, appropriate knowledge is needed regarding anticoagulant drug disposition and resulting efficacy and safety in this population. We review general considerations about oral drug disposition in patients after bariatric surgery, as well as existing literature on oral anticoagulation after bariatric surgery. Overall, available evidence on therapeutic anticoagulation is very limited, and individual drug studies are necessary to learn how to safely and effectively use the direct oral anticoagulants. Given the sparsity of currently available data, it appears most prudent to use warfarin with international normalized ratio monitoring, and not direct oral anticoagulants, when full-dose anticoagulation is needed after bariatric surgery.

Anticoagulant activity of oral rivaroxaban in healthy dogs

Rivaroxaban is an oral, direct factor Xa inhibitor used in human thrombotic disorders. In view of the in vitro concentration dependent anticoagulant effects of rivaroxaban in dogs, the time course of its anticoagulant effects was characterized in healthy dogs. Twenty-four healthy Beagles were randomized into three groups (n = 8 per group) and received orally either a placebo or 20 mg rivaroxaban once or twice at an 8 h interval. Fifteen blood samples were collected over a 30 h period, and blindly assayed for prothrombin time (PT), activated partial thromboplastin time (aPTT), tissue factor induced thrombin generation (TG) and anti-factor Xa activity. Thromboelastography (TEG) was evaluated at 0, 1, 4, 8 and 24 h. Peak/baseline anticoagulant effect ratios were analyzed with generalized linear models using β distributions and times to return to baseline with survival analyses (α = 0.05). Peak/baseline anticoagulant effect ratios of PT, aPTT, anti-factor Xa activity, TG and R (TEG) differed significantly between placebo and both rivaroxaban groups (P <0.0001). The peak anticoagulant effect of rivaroxaban occurred 1.5 to 2 h after dosing. The median return to baseline occurred significantly sooner (P <0.01) with 20 mg rivaroxaban administered once (7.9-18.7 h) versus twice (17.5-26.8 h). The inter-individual variability differed amongst assays, but overall was moderate to large. No adverse effects were recorded. Twice oral administration of 2 mg/kg rivaroxaban at an 8 h interval maintained 24 h anticoagulant activity, but larger studies are needed to establish guidelines for the use of rivaroxaban in dogs.

[Monitoring of NOAC]

BACKGROUND

Monitoring non-vitamin K antagonist oral anticoagulants (NOAC) is usually not necessary; however, in some patients it may prove beneficial.

OBJECTIVES

Patient subgroups who may profit from monitoring were identified, and methods of monitoring (including assessment of which coagulation parameters are affected by NOAC) are described.

MATERIALS AND METHODS

We searched the PubMed database for each of the search terms, "NOAC", "DOAC", "rivaroxaban", "dabigatran", and "apixaban", in combination with one of the terms, "monitoring", "measurement", "measuring", or "assessment". The results were compiled and reviewed.

RESULTS

Monitoring is most advantageous in emergency cases with severe bleeding where drug activity needs to be assessed. It can also help in deciding for or against lysis therapy after acute stroke in patients taking NOAC. Furthermore, it can also identify compliance problems and help in planning periprocedural management. There are quantitative measurement methods which measure plasma concentrations exactly and qualitative methods which only allow for a rough estimate or a general confirmation of drug activity. Recommended quantitative measurement methods are diluted thrombin time for dabigatran, and anti-factor Xa activity (calibrated) for rivaroxaban and apixaban.

CONCLUSIONS

Several patient subgroups may profit from monitoring of NOAC plasma concentration. One should, however, take several issues into consideration before measurements, such as the objective of each individual measurement, possible consequences (e. g., dose adjustment), and which measurement method to pick.

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.

Postoperative Bleeding After Administration of a Single Dose of Rivaroxaban to a Patient Receiving Antiretroviral Therapy

A 62-year-old man was admitted to hospital for elective revision of a left total hip arthroplasty. His history was significant for human immunodeficiency virus (HIV) infection for which he was taking the following antiretroviral agents (ARVs): etravirine, ritonavir, darunavir, raltegravir and tenofovir/emtricitabine. Rivaroxaban 10 mg daily was commenced on the second postoperative day for venous thromboembolism (VTE) prophylaxis. Approximately 24 h later, the patient developed hypotension and anaemia, accompanied by thigh swelling due to bleeding at the surgical site. Fluid resuscitation was commenced with red cell transfusion. The prothrombin time (PT) was prolonged at 24.3 (10.6–15.3) s, and a rivaroxaban level taken 24 h after administration was 75 ng/mL. Rivaroxaban was ceased, the PT normalised within 24 h of stopping the drug, and the patient made an uneventful recovery. None of the other coadministered drugs are known to interact with rivaroxaban, or are likely to, based on their metabolic pathways. Rivaroxaban, a substrate for cytochrome P450 (CYP) 3A4 and P-glycoprotein (P-gp), is contraindicated in patients concomitantly treated with strong inhibitors of both these systems, e.g. protease inhibitors (PIs) such as ritonavir (based on in vitro data and a pharmacokinetic study in healthy volunteers). No published data are available on the PI darunavir, a moderate inhibitor; however, concomitant use with rivaroxaban should also be avoided. A prolonged PT and a rivaroxaban trough level greater than eight times that predicted from pharmacokinetic modelling suggests that bleeding was due to increased exposure to rivaroxaban, probably due to an interaction with ritonavir and darunavir. This is supported by a Drug Interaction Probability Scale (DIPS) score of 8. An interaction between a single dose of rivaroxaban and ARVs may be clinically significant; therefore, the patient’s medication history should be extensively evaluated to identify any potential interactions.

Interpretation of coagulation test results under direct oral anticoagulants

Diagnostic of global coagulation parameters is part of the daily clinical routine practice in conservative as well in operative disciplines. The correct interpretation of in vitro test results in context to the ex vivo influence of anticoagulant drugs and the in vivo hemostatic system of the individual patient is dependent on the doctors clinical and laboratory experience. This article shortly reviews the laboratory interference of oral anticoagulants including the target-specific inhibitors dabigatran, rivaroxaban and apixaban on coagulation parameters and discusses the potential of several methods for measuring the anticoagulant effect of the direct oral anticoagulants.

Determination of dabigatran, rivaroxaban and apixaban by ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) and coagulation assays for therapy monitoring of novel direct oral anticoagulants

BACKGROUND

Three novel direct oral anticoagulants (DOACs) have recently been registered by the Food and Drug Administration and European Medicines Agency Commission: dabigatran, rivaroxaban, and apixaban. To quantify DOACs in plasma, various dedicated coagulation assays have been developed.

OBJECTIVE

To develop and validate a reference ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) method and to evaluate the analytical performance of several coagulation assays for quantification of dabigatran, rivaroxaban, and apixaban.

METHODS

The developed UPLC-MS/MS method was validated by determination of precision, accuracy, specificity, matrix effects, lower limits of detection, carry-over, recovery, stability, and robustness. The following coagulation assays were evaluated for accuracy and precision: laboratory-developed (LD) diluted thrombin time (dTT), Hemoclot dTT, Pefakit PiCT, ECA, Liquid anti-Xa, Biophen Heparin (LRT), and Biophen DiXal anti-Xa. Agreement between the various coagulation assays and UPLC-MS/MS was determined with random samples from patients using dabigatran or rivaroxaban.

RESULTS

The UPLC-MS/MS method was shown to be accurate, precise, sensitive, stable, and robust. The dabigatran coagulation assay showing the best precision, accuracy and agreement with the UPLC-MS/MS method was the LD dTT test. For rivaroxaban, the anti-factor Xa assays were superior to the PiCT-Xa assay with regard to precision, accuracy, and agreement with the reference method. For apixaban, the Liquid anti-Xa assay was superior to the PiCT-Xa assay.

CONCLUSIONS

Statistically significant differences were observed between the various coagulation assays as compared with the UPLC-MS/MS reference method. It is currently unknown whether these differences are clinically relevant. When DOACs are quantified with coagulation assays, comparison with a reference method as part of proficiency testing is therefore pivotal.

Use of hemodialysis for the treatment of intracerebral hemorrhage in patients on dabigatran with normal renal function

Dabigatran is a direct thrombin inhibitor which is approved by the Food and Drug Administration (FDA) for prevention of embolic stroke in patients with atrial fibrillation. Dabigatran has been shown to be non- inferior to warfarin in preventing stroke in patients with atrial fibrillation [1, 6]. The rate of major bleeding in patients taking dabigatran is also similar to that seen in patients on warfarin [1]. Unlike warfarin, there is currently no antidote available for reversal of anticoagulant effects of dabigatran [2, 3]. Dabigatran is excreted renally and accumulates in patients with acute kidney injury (AKI). Hemodialysis has been reported to increase clearance of dabigatran in patients with acute kidney injury and life-threatening bleeding [4, 5]. We present two cases of dabigatran-associated intracranial hemorrhage where hemodialysis was used to accelerate clearance of dabigatran from the blood in patients with normal renal function.

Measurement of dabigatran in standardly used clinical assays, whole blood viscoelastic coagulation, and thrombin generation assays

Dabigatran, a direct thrombin inhibitor, is increasingly used clinically as one of the new oral anticoagulants. This review summarizes the assays available to measure its activity and includes the relative sensitivity of the different assays for this agent. In addition to plasma-based clotting tests, assays commonly used in surgical/emergency settings, such as activated clotting time and thromboelastometry/thromboelastography, are reviewed. In addition, the thrombin generation assay is discussed as an important method to determine the potential risk of thrombosis or bleeding and its relevance to the measurement of direct thrombin inhibitors.

Hypercoagulable states: an algorithmic approach to laboratory testing and update on monitoring of direct oral anticoagulants

Hypercoagulability can result from a variety of inherited and, more commonly, acquired conditions. Testing for the underlying cause of thrombosis in a patient is complicated both by the number and variety of clinical conditions that can cause hypercoagulability as well as the many potential assay interferences. Using an algorithmic approach to hypercoagulability testing provides the ability to tailor assay selection to the clinical scenario. It also reduces the number of unnecessary tests performed, saving cost and time, and preventing potential false results. New oral anticoagulants are powerful tools for managing hypercoagulable patients; however, their use introduces new challenges in terms of test interpretation and therapeutic monitoring. The coagulation laboratory plays an essential role in testing for and treating hypercoagulable states. The input of laboratory professionals is necessary to guide appropriate testing and synthesize interpretation of results.

New oral anticoagulants in patients with nonvalvular atrial fibrillation: a review of pharmacokinetics, safety, efficacy, quality of life, and cost effectiveness

Atrial fibrillation (AF) continues to be a leading cause of cerebrovascular morbidity and mortality resulting from cardioembolic stroke. Oral anticoagulation therapy has been shown to decrease the incidence of cardioembolic stroke in patients with AF by more than 50%. Appropriate use of anticoagulation with vitamin K antagonists requires precise adherence and monitoring. A number of factors that potentially induce patients’ dissatisfaction reduce quality of patient life. New direct oral anticoagulants, such as the direct factor Xa inhibitors rivaroxaban, apixaban, edoxaban, and the thrombin inhibitor dabigatran, were developed to overcome the limitations of the conventional anticoagulant drugs. However, models to optimize the benefit of therapy and to ensure that therapy can be safely continued are missing for the new oral anticoagulants. This review will briefly describe the new oral anticoagulants dabigatran, rivaroxaban, apixaban, and edoxaban with focus on their use for prevention of embolic events in AF. Moreover, it will discuss the safety, efficacy, cost data, and benefit for patients’ quality of life and adherence.

The role of prothrombin complex concentrates in reversal of target specific anticoagulants

Over the past several years a new era for patients requiring anticoagulation has arrived. The approval of new target specific oral anticoagulants offers practitioners several advantages over traditionally used vitamin K antagonist agents including predictable pharmacokinetics, rapid onset of action, comparable efficacy and safety, all without the need for routine monitoring. Despite these benefits, hemorrhagic complicates are inevitable with any anticoagulation treatment. One of the major disadvantages of the new oral anticoagulants is lack of specific antidotes or reversal agents for patients with serious bleeding or need for urgent surgery. As use of the new target specific oral anticoagulants continues to increase, practitioners will need to understand both the pharmacodynamics and pharmacokinetic properties of the agents, as well as, the available literature with use of non-specific therapies to reverse anticoagulation. Four factor prothrombin complex concentrates have been available for several years in Europe, and recently became available in the United States with approval of Kcentra. These products have shown efficacy in reversing anticoagulation from vitamin K antagonists, however their usefulness with the new target specific oral anticoagulants is poorly understood. This article will review the properties of dabigatran, rivaroxaban and apixaban, as well as the limited literature available on the effectiveness of prothrombin complex concentrates in reversal of their anticoagulant effects. Additional studies are needed to more accurately define the role of prothrombin complex concentrates in patients with life threatening bleeding or who require emergent surgery, as current data is both limited and conflicting.

Direct oral anticoagulants--interference with laboratory tests and mechanism of action

Direct oral anticoagulants (DOACs) have been established and already registered for clinical use on a wide basis in the United States and Europe. Different from the vitamin K antagonists (VKA), their mode of action is based on the direct inhibition of the single coagulation enzymes factor Xa or IIa. Other laboratory tests of hemostasis, such as the global tests prothrombin time (PT/INR) and activated partial thromboplastin time (APTT), or various functional coagulation assays involving generation of factor Xa or IIa for their endpoints, can be negatively influenced by the presence of the anticoagulant in the test sample. This interference has been well documented for rivaroxaban, apixaban, and dabigatran and is most prominent during the first hours after intake of the respective agent. Thus, the potential influence of DOACs has always to be considered when interpreting abnormal functional coagulation assays.

A Review of and Recommendations for the Management of Patients With Life-Threatening Dabigatran-Associated Hemorrhage

Dabigatran is an oral direct thrombin inhibitor that is approved for the prevention of stroke and systemic embolism in nonvalvular atrial fibrillation. Dabigatran has several advantages over warfarin including predictable pharmacokinetics and pharmacodynamics which eliminates the need for routine laboratory monitoring, superiority over warfarin in preventing stroke, or systemic embolism without having an increased risk of bleeding. However, as with any anticoagulant, there remains a real chance of bleeding, including major or life-threatening hemorrhage. Many physicians feel comfortable managing bleeding complications on older anticoagulants like warfarin and heparin, due to extensive experience with the medications along with antidotes to reverse their effects as well as established protocols for treating anticoagulant-associated hemorrhage. However, most physicians have limited clinical experience with dabigatran, there is no specific antidote for dabigatran reversal and there is a paucity of protocols, guidelines, and recommendations for how to manage dabigatran-associated hemorrhage. In this review, we present a case series of patients admitted to our institution for management of bleeding while receiving dabigatran. We retrospectively reviewed these cases to evaluate the efficacy and rationale of the various anticoagulation reversal strategies employed in the context of the existing evidence found in the literature. Specific focus is placed on the therapies utilized and the coagulation studies used to manage these patients.

Edoxaban

Vitamin K antagonists (VKAs) remain the standard therapy for anticoagulation in prevention and treatment of venous thromboembolism (VTE) and for the prevention of stroke in atrial fibrillation (AF). Due to numerous limitations of VKAs, target-specific oral anticoagulants have been developed. Edoxaban is a direct activated factor X inhibitor with attractive features among which are once daily dosing, no need for routine monitoring, and minimal drug–drug interactions. In patients undergoing orthopedic surgery, edoxaban was superior to enoxaparin in preventing VTE. Furthermore, a recent large-scale phase III trial in patients with symptomatic VTE demonstrated that edoxaban was noninferior to warfarin in preventing recurrent VTE and reduced bleeding. In the largest trial of anticoagulation in patients with AF to date, edoxaban was noninferior to warfarin in the prevention of stroke or systemic embolism and reduced bleeding and cardiovascular mortality. This review provides an overview of the pharmacology, clinical trial results, and potential indications for edoxaban.

Postoperatives Management der Gerinnung

<b><i>Hintergrund: </i></b>Das Gerinnungsmanagement in der postoperativen Phase stellt eine komplexe Herausforderung dar. Einerseits führt eine bereits präoperativ vorbestehende oder intraoperativ erworbene Beeinträchtigung der Blutgerinnung zu einem erhöhten Risiko für Nachblutungen. Andererseits sind Patienten in der postoperativen Phase einem erhöhten Risiko für thromboembolische Komplikationen ausgesetzt. Zudem drängen vermehrt neue orale Antikoagulanzien und Thrombozytenaggregationshemmer auf den Markt, für deren perioperativen Einsatz noch wenig Erfahrung besteht. <b><i>Methode: </i></b>Literaturübersicht. <b><i>Ergebnisse: </i></b>Das postoperative Gerinnungsmanagement sollte individualisiert nach einer Diagnostik mit klassischen Gerinnungstests und Point-of-Care(POC)-Diagnoseverfahren erfolgen. Verglichen mit dem intraoperativen Gerinnungsmanagement bestehen Unterschiede. <b><i>Schlussfolgerungen: </i></b>Das Ziel des postoperativen Gerinnungsmanagements ist eine Gerinnungsaktivität, die eine suffiziente Wundheilung zulässt, ohne thromboembolische Ereignisse zu begünstigen. Im Falle einer postoperativen Blutung sollte zur Diagnostik neben den klassischen Gerinnungstests auf viskoelastische POC-Verfahren zurückgegriffen werden. Neben der bedarfsadaptierten Substitution von Gerinnungsfaktoren ist die Aufrechterhaltung der Rahmenbedingungen der Gerinnung von entscheidender Bedeutung (Normothermie, physiologischer pH-Wert, Normokalziämie). Die Fortführung einer bestehenden Antikoagulation mit neuen oralen Antikoagulanzien ist eine Einzelfallentscheidung. Für ihren perioperativen Einsatz gib es noch keine Leitlinien.