Apixaban Levels Research Articles

Apixaban removal during emergency surgery for type a acute aortic dissection. a prospective cohort study

Background: Acute type A aortic dissection (ATAAD) has a high mortality, and acute aortic repair is the only curative treatment. In patients treated with factor Xa (FXa) inhibitors, the risk of severe disease-related complications such as cardiac tamponade and hemodynamic shock must be balanced against the potential for severe perioperative bleeding. The aim was to study intraoperative changes in plasma levels of the FXa inhibitor apixaban when using hemoadsorption during acute thoracic aortic repair. Materials and Methods: This is a single-center prospective cohort study. Eight apixaban-treated patients presenting with ATAAD underwent acute thoracic aortic repair with intraoperative hemoadsorption with CytoSorb®. Apixaban concentrations were measured at the start of cardiopulmonary bypass (CPB), and after 5, 15, 30, 60 and 90 minutes of CPB, at CPB weaning, 30 minutes after CPB weaning and 24 hours postoperatively, using ultraperformance liquid chromatography mass spectrometry (UPLC-MS). Results: After 30 minutes of CPB with hemoadsorption, mean apixaban concentration (± SD) was reduced by 59% from 108 (± 69) µg/L to 44 (± 20) µg/L (P = 0.009). There was a further reduction to 37 (± 17) µg/L at CPB weaning (P = 0.008). Apixaban concentration displayed an increase to 56 (± 29) µg/L 24 hours postoperatively (P = 0.01). In-hospital mortality was 25%. Mean 24H chest tube drainage volume was 621 (± 136) mL. Conclusion: Intraoperative hemoadsorption lowers apixaban levels in patients undergoing emergency surgery for ATAAD. Further research is needed to determine its impact on perioperative bleeding complications and mortality.

Plasma apixaban levels and thrombin generation assay in patients with atrial fibrillation with dose reduction criteria of apixaban

Abstract Background Off-label reduced-dose apixaban is commonly prescribed in patients with atrial fibrillation (AF). However, the pharmacokinetic data of apixaban according to the dosage and label is limited especially in those with dose reduction criteria of apixaban. Purpose We investigated the apixaban plasma concentration (PC) and thrombin generation assay (TGA) parameters across different apixaban dose settings. Methods We enrolled 398 non-valvular AF patients with more than single-dose reduction criteria of apixaban and divided them into three groups: (1) on-label standard dose (single dose-reduction criterion with standard-dose of apixaban 5mg twice daily, n=173); (2) off-label reduced-dose (single dose-reduction criterion with apixaban 2.5mg twice daily, n=61); and (3) on-label reduced-dose (two or more dose-reduction criteria with apixaban 2.5mg twice daily, n=164). Apixaban PC by anti-Xa assay and TGA parameters of these three groups were compared at the trough level. Results The on-label standard dose group showed a higher PC than the on-label reduced dose (124.7 vs. 80.3 ng/mL, p<0.001), and the on-label reduced dose exhibited a higher PC than the off-label reduced dose (80.3 vs. 53.2 ng/mL, p=0.031) (Figure). The TGA parameters displayed a similar pattern of differences, with the on-label standard dose group tends to show the least thrombogenic profiles (Figure). Lower creatinine clearance (CrCl), older age, and female sex were statistically significant predictors for a higher apixaban PC by multivariable regression model (p<0.001, p=0.043, and 0.023, respectively), and CrCl was the most influential variable to dichotomize apixaban PC in all three groups (Figure). Conclusions Off-label reduced-dose apixaban group exhibited significantly lower apixaban level than both on-label standard dose and on-label reduced-dose apixaban groups, suggesting the importance of adhering to current dose-reduction criteria for maintaining appropriate apixaban levels. Caution is particularly advised in off-label under-dosing for patients with high creatinine clearance. Further investigation into the impact of off-label under-dosing on clinical outcomes is essential to guide optimal therapeutic strategies.

Management of apixaban anticoagulation in a patient requiring therapeutic plasma exchange: a case report and a literature review.

Therapeutic plasma exchange (TPE) is used as an effective treatment modality for a variety of autoimmune disorders. Apart from its desired effect of removing pathological blood components, it also can remove coagulation factors and drugs. Currently, there is an insufficient amount of information regarding the use of direct oral anticoagulants in this setting. In this article, we present a case report of a patient with myasthenia gravis and chronic anticoagulation with apixaban who underwent a series of TPE while continuing apixaban treatment. We observed that only 10% of daily dose was removed by the procedure and plasma levels of apixaban corresponded with expected range. TPE was not associated with shortened drug plasma half-life. We did not observe any significant alteration of apixaban pharmacokinetics during the period of TPE therapy, as well as no thrombotic or bleeding events. This case report supports the use of apixaban in patients treated by TPE, nevertheless, to firmly establish apixaban efficacy and safety profile in this clinical setting further research is needed.

Effects of the antitumor drugs adagrasib and asciminib on apixaban metabolism in vitro and in vivo

Apixaban is an oral anticoagulant that directly inhibits the target Factor Xa (FXa). In this study, we focused on the in vivo and in vitro effects of adagrasib and asciminib on apixaban metabolism, to discover potential drug-drug interactions (DDI) and explore their inhibitory mechanisms. The levels of apixaban and its metabolite, O-desmethyl-apixaban (M2), were determined by ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). In vitro evaluation, the maximum half inhibitory concentration (IC50) of adagrasib in rat liver microsomes (RLM) and human liver microsomes (HLM) against apixaban was 7.99 μM and 117.40 μM, respectively. The IC50 value of asciminib against apixaban in RLM and HLM was 4.28 μM and 18.42 μM, respectively. The results of the analysis on inhibition mechanisms showed that adagrasib inhibited the metabolism of apixaban through a non-competitive mechanism, while asciminib inhibited the metabolism of apixaban through a mixed mechanism. Moreover, the interaction of apixaban with adagrasib and asciminib in Sprague-Dawley (SD) rats was also investigated. It was found that the pharmacokinetic characteristics of apixaban were significantly changed when combined with these two antitumor drugs, where AUC(0-t), AUC(0-∞), t1/2, Tmax, and Cmax were increased, while CLz/F was significantly decreased. But both drugs did not appear to affect the metabolism of M2 in a significant way. Consistent results from in vitro and in vivo demonstrated that both adagrasib and asciminib inhibited the metabolism of apixaban. It provided reference data for the future clinical individualization of apixaban.

Prothrombin complex concentrate for emergency surgery in patients on oral Xa-inhibitors

BackgroundIt is uncertain whether prothrombin complex concentrate (PCC) improves hemostasis in patients on treatment with oral factor Xa-inhibitors (XaI) who require emergency surgery. ObjectivesTo evaluate whether, in patients with therapeutic levels of oral XaI, preoperative PCC prevents excessive bleeding during and after emergency surgery and is not associated with thrombotic complications. MethodsWe conducted a prospective cohort study wherein a fixed 2000 IU dose of 4-factor PCC was given to patients taking oral XaI with plasma XaI levels of at least 75 ng/mL before the emergency surgery with an expected blood loss of at least 50 mL. Patients were followed for 30 days. The primary efficacy outcome was the incidence of normal or mildly abnormal surgical hemostasis, as assessed by the surgeon; primary safety outcome was the incidence of thromboembolic events within 7 days. ResultsWe included 20 patients, of which 50% were female, on apixaban (75%) or rivaroxaban (25%) with median XaI level of 128 ng/mL (range, 77-497 ng/mL). The median duration of surgery was 2 hours 42 minutes (range, 15 minutes to 8 hours 17 minutes). Normal or mildly abnormal hemostasis was observed in 16 patients (80%); 2 patients had moderately abnormal and 2 had severely abnormal hemostasis, 1 each of those was considered due to local or technical factors. There were 4 deaths (20%) secondary to underlying disease and 1 incidental pulmonary embolism in a patient with cancer. ConclusionA fixed dose of PCC appears to control hemostasis in patients with therapeutic plasma levels of apixaban or rivaroxaban requiring emergency surgery.

Does in vitro hemolysis affect measurements of plasma apixaban concentration by UPLC-MS and anti-Xa assay?

Hemolytic interference may impact various laboratory tests, including coagulation analyses. Apixaban is the most commonly used direct oral anticoagulant in Norway, and there is lacking knowledge on how apixaban concentration measurements might be influenced by hemolysis. Moreover, hemolysis-induced alterations in apixaban levels could potentially impact the risk of bleeding in specific clinical scenarios. We wanted to study whether hemolysis would increase apixaban concentration and investigate the impact of hemolytic interference on apixaban concentration measurements. Blood samples from 20 apixaban-treated patients and 8 healthy controls were hemolyzed in vitro by a freeze method. The degree of hemolysis was measured with plasma free hemoglobin (PfHb) at baseline and two levels of hemolysis. Apixaban concentration was measured in plasma using both the chromogenic anti-Xa method and the ultraperformance liquid chromatography mass spectrometry (UPLC-MS). Thrombin generation assay was performed to assess coagulability. UPLC-MS measurements showed a mean concentration change of -1.66% (±3.2%, p = 0.005) and anti-Xa assay showed a mean concentration change of 3.37% (±6.5%, p = 0.09) with increasing hemolysis. Thrombin generation lagtime decreased, and endogenous thrombin potential and peak thrombin increased with increasing hemolysis in both the control group and the apixaban group. Apixaban concentration measurements by anti-Xa assay and UPLC-MS were not affected by hemolysis to a clinically relevant extent. Furthermore, hemolysis did not lead to hypocoagulability when assessed by thrombin generation.

Plasma levels of apixaban and rivaroxaban in patients with venous thromboembolism

Plasma levels of apixaban and rivaroxaban in patients with venous thromboembolism

Acute severe renal failure in a patient receiving apixaban: a case report

Because there is little clinical experience with apixaban in patients with severe renal impairment and non-valvular atrial fibrillation, the European Medicines Agency does not advise using it to prevent strokes in these patients. However, only a small number of pharmacokinetic and pharmacodynamic investigations showed how crucially different elimination pathways contribute to the clearance of apixaban. A 74-year-old male patient who was receiving apixaban treatment for stroke prevention in atrial fibrillation was referred to our hospital because of acute severe renal failure brought on by dehydration and abnormally elevated apixaban plasma levels. The patient was treated only with intravenous fluid therapy; serum creatinine recovered slowly over the course of six days, but plasma apixaban levels recovered quickly. No bleeding events have been recorded. Our experience demonstrates the safety profile of apixaban in cases of severe renal failure, but it also emphasizes the need for more research to confirm this evidence.

Use of apixaban in children awaiting heart transplantation.

The use of apixaban in the pediatric cardiac population is expanding. We describe our apixaban dosing and monitoring strategy in children and young adults awaiting heart transplantation, along with outcomes related to bleeding and thrombosis during wait-list and early post-transplant periods. This study is a retrospective, single-center analysis of all patients receiving apixaban while awaiting cardiac transplantation. Weight-based dosing was monitored with peak drug-specific anti-Xa chromogenic analysis. Significant post-operative bleeding defined by chest tube output or need for surgical intervention. From September 2020 to December 2022, 19 patients, median age 13.5 years (6.1, 15.8 years), weighing 48.9 kg (15.4, 67.6) received apixaban while awaiting transplant. Indication for apixaban was prophylaxis (n = 18, 3 with ventricular assist devices) and treatment of thrombus (n = 1). There were no clinically relevant non-major or major bleeding, nor thrombotic events while awaiting transplant. The median time from last apixaban dose to arrival in the operating room was 23.2 h (15.6-33.8), with median random apixaban level of 37 ng/mL (28.3, 59), 6.3 h (4.8, 8.4) prior to arrival in the operating room. In this study, 32% of patients had significant post-operative bleeding based on chest tube output post-transplant or need for intervention. No patients meeting criteria for significant post-operative bleeding were thought to be attributable to apixaban. Careful use of apixaban can be safe and effective while awaiting heart transplant. There was no appreciable increase in peri-operative bleeding. The use of apixaban is promising in providing safe, predictable and efficacious anticoagulation while avoiding additional patient stressors.

Incorrect community dosing leading to high apixaban levels in a patient with a hip fracture.

Incorrect community dosing leading to high apixaban levels in a patient with a hip fracture.

Safety of endoscopic ultrasound-guided tissue acquisition with uninterrupted direct oral anticoagulation in a swine model

Abstract Background and study aims The risk of bleeding with endoscopic ultrasound-guided tissue acquisition (EUS-TA) in patients on uninterrupted antithrombotic agents is unknown. This study aimed to assess the safety of EUS-TA without discontinuing direct oral anticoagulants. Methods Twenty pigs were randomized (1:1) to oral apixaban or placebo. Treatment was administered for 3 days before and 3 days after EUS-TA of the pancreas. Primary endpoint was occurrence of clinically significant bleeding events (CSBEs), defined as a composite outcome of drop in hemoglobin ≥ 2 g/dL and evidence of intraprocedural or post-procedure bleeding. Secondary outcome was cytopathological adequacy of acquired specimens. Endoscopists and pathologists were blinded to the treatment arm. Results Total of 80 tissue samples were obtained. CSBE occurred in one animal with apixaban levels above the upper limit (P = 1). Intraprocedural bleeding occurred in five animals (25 %), four of which from the apixaban group. Hematoma at necropsy was found in 10 animals (50 %), six of which were on apixaban. Median drop in hemoglobin was similar in both groups. Adequacy of specimens for cytology and pathology evaluation was confirmed in 20 of 20 and 19 of 20 animals, respectively. Conclusions In this pilot preclinical trial, EUS-TA under apixaban showed a trend toward higher minor bleeding events but did not increase CSBE or prevent adequate cytopathological evaluation.

Real-world use of apixaban for the treatment and prevention of thrombosis in children with cardiac disease

BackgroundDirect oral anticoagulants use in pediatric cardiology is poorly defined. ObjectiveWe present the largest experience of apixaban use in children with heart disease, using weight- and level-based dosing. MethodsRetrospective single-center analysis of cardiac patients ≤19 years treated with apixaban. Patients were evaluated for safety (clinically relevant non-major [CRNM] or major bleeding; thrombotic events) and effectiveness (thrombus improvement by imaging). Peak drug-specific anti-Xa chromogenic assay results (“apixaban levels”) were analyzed. ResultsOver 3 years (5/2018-9/2021), 219 children, median age 6.8 years (0.3-19), median weight 20.8 kg (4.8-160) received apixaban, totaling 50,916 patient days. Of them, 172 (79%) warranted thromboprophylaxis and 47 (21%) thrombosis treatment (with 10 arterial, 19 venous, 15 intracardiac, and 3 pulmonary). The median initial peak apixaban level was 165 ng/mL (23-474; n = 125) in the prophylaxis subgroup and 153 ng/mL (30-450; n = 33) in the treatment subgroup; dosage was adjusted in response to levels in 25% of the patients. There were 4 bleeding safety events (3 CRNM; 1 major, hemoptysis complicating empyema); the serious bleeding event rate was 2.9 per 100 patient-years of apixaban. Minor bleeding events (42) were noted in 18 patients, with an additional 2 having leukopenia, 1 transaminitis, and 3 rashes. An improvement in thrombosis was seen in 95% of the treated patients with available follow-up imaging (37/39 patients). ConclusionApixaban use was feasible with a low rate of adverse events across a diverse pediatric cardiac population using commercially available tablets dosed to weight and adjusted based on peak apixaban levels.

Plasma apixaban levels in Chinese patients with chronic kidney disease-Relationship with renal function and bleeding complications.

Introduction: Accumulation of apixaban in plasma is a major concern in patients with chronic kidney disease (CKD). Studies that investigated plasma apixaban level in CKD patients and its association with clinically significant events are scarce. Methods: Patients with CKD Stage 1-4 who were taking apixaban, either 2.5mg BD or 5mg BD were recruited. The peak and trough plasma apixaban level were measured after 2h and 12h of last dose respectively. The results were correlated with renal function and clinical events during the period of follow-up from 1 January 2018 to 31 October 2021. Results: 141 patients (CKD Stage 1, n = 12; Stage 2, n = 74; Stage 3, n = 48, stage 4, n = 7) were included for analysis. The plasma peak and trough apixaban were significantly higher in patients with CKD stage 3 when compared with those having CKD stage 2 and 1 (peak levels: 223.4 ± 107.8ng/ml vs. 161.0 ± 55.2ng/ml vs. 126.6 ± 30.2ng/ml; trough levels: 118.3 ± 67.9ng/ml vs. 81.2 ± 33.0ng/ml vs. 51.9 ± 31.1ng/ml, p < 0.05 or all) in patients taking 5mg BD. Plasma trough apixaban level was negatively correlated with eGFR in patients taking 5mg BD (r 2 = -0.174, p < 0.001) and 2.5mg BD (r 2 = -0.215, p < 0.05). The plasma peak and trough apixaban level correlated with PT (r 2 = 0.065, p = 0.003 and r 2 = 0.096, p < 0.01 respectively). Multivariate analysis showed that plasma trough apixaban levels were associated with the risk of bleeding complications (Odd ratio: 1.011, 95% CI:1.002-1.021, p = 0.023). Conclusion: The plasma apixaban level shows a trend of increase with worsening renal function, and an increase in the plasma apixaban level is suggestive of an increased risk of bleeding complications in patients with CKD. Further large-scale prospective studies are needed to evaluate relationship between plasma apixaban level and renal function as well as safety outcome in CKD patients. Moreover, the role of drug level monitoring should be prospectively evaluated for dosage optimization and the minimization of bleeding risks in CKD patients.

Abstract 11900: Should Venous Thromboembolism Patients Treated With DOACs Be Dose Adjusted Like Patients With Atrial Fibrillation: Lessons From Apixaban

Introduction: In contrast to atrial fibrillation (AF), dose adjustment of apixaban and other DOACs is not recommended for pts with DVT or PE (VTE). Median DOAC levels were lower in VTE trials (e.g. apixaban 5-mg BID, AF 171 and 103 ng/mL vs. DVT 132 and 63 ng/mL, peak and trough, respectively), the result of a younger, lower weight population with better kidney function. Thus, VTE patients who meet or approach the apixaban dose reduction criteria may have levels far in excess of what’s needed to prevent recurrence. Hypothesis: Apixaban over exposure occurs in VTE pts at risk for elevated apixaban levels. Methods: Patients ≥ 75 yrs of age who had clinical markers that identified them as being at high risk for over exposure, including: 1) apixaban AF dose risk reduction criteria (age ≥ 80, creatinine ≥ 1.5, and wt ≤ 60-kg) and 2) approaching but not meeting dose reduction criteria (e.g. creatine 1.4, weight 65-kg) had a DOAC level measured at their anticoagulation clinic appointment. Levels were determined using liquid chromatography-mass spectrometry. Clinical decisions were made based on the “expected” apixaban levels. Results: Apixaban levels were obtained in 15 male pts. All 10 pts who were initially treated with apixaban 5-mg (2 of whom met the AF dose reduction criteria) had supratherapeutic apixaban levels on 5-mg BID. Of the 5 pts treated initially with apixaban 2.5-mg BID, 3 had adequate apixaban levels, while the other 2 had trough levels that were on the lower side. All 3 pts who met the AF dose reduction criteria (1 treated initially with 2.5-mg) had an adequate apixaban level on 2.5-mg BID. Conclusions: Apixaban treated VTE pts who meet or approach the AF dose reduction criteria are candidates for apixaban dose reduction, especially in light of the fact that peak and trough levels for VTE pts in general are lower than pts with AF.

Modified thromboelastometric tests provide improved sensitivity and specificity to direct oral anticoagulants compared to standard thromboelastometric tests in-vitro

BackgroundThe detection of direct oral anticoagulants (DOACs) is still challenging but important in emergency patients. We recently demonstrated that modified thromboelastometry can detect rivaroxaban and dabigatran. Data on the detection rates of modified compared to standard thromboelastometric tests of apixaban and edoxaban, are missing. The aim of this in-vitro dose-effect-study was to add data on these DOACs and to evaluate thromboelastometric tests in-vitro using data of both studies.MethodsThe study was approved by the Ludwig-Maximilians-University ethics committee (No 17-525-2). Written informed consent was obtained from all individuals. Blood samples of healthy volunteers and samples of 10 volunteers for each DOAC were used. Blood samples were spiked with six different concentrations of edoxaban and apixaban (0ng/ml; 31.25ng/ml; 62.5ng/ml; 125ng/ml; 250 ng/ml; 500ng/ml). Modified tests (low-tissue-factor test TFTEM and ecarin-based test ECATEM) as well as standard tests (e.g. FIBTEM) analyzing extrinsic pathway of coagulation were used. Receiver operating characteristics analyzes were performed as well as regression analyzes.ResultsTFTEM CT correlated well with anti-Xa levels of apixaban and edoxaban (apixaban: r2 = 0.8064 p < 0.0001; edoxaban: r2 = 0.8603; p < 0.0001). The detection of direct FXa inhibitors (> 30 ng/mL) was successful with FIBTEM CT with a sensitivity and specificity of 81% and 90%, respectively. As expected, ECATEM CT was not prolonged by direct FXa-inhibitors due to its specificity for direct thrombin inhibitors. Again, TFTEM CT provided the highest sensitivity and specificity for the detection of direct FXa inhibitors with 96% and 95%, respectively. ECATEM test showed 100% sensitivity and 100% specificity for the detection of dabigatran.ConclusionsOur study presents modified thromboelastometric tests with improved detection of even low DOAC concentrations > 30 ng/mL, including apixaban in-vitro. The study thus complements the previously published data on dabigatran and rivaroxaban. Validation studies must confirm the results due to the explanatory design of this study.

A Review of Pharmacogenetics of Anticoagulant Therapy

Variances in the patients’ outcomes have been a well-documented challenge in anticoagulant therapy. A clinical encounter with a thromboembolic or a hemorrhagic event, due to subtherapeutic or adverse effects of an anticoagulant, is often managed by switching the anticoagulant agent into another, which is more specific and direct-acting. This management approach is usually associated with a financial burden. Additionally, the certainty of achieving better efficacy and safety profile is still questionable. Genetic variants affecting the protein sites that are involved in the anticoagulant pharmacokinetic and pharmacodynamics interactions have been suggested to contribute to the variability in the response to anticoagulant therapy. The current work reviewed the studies investigating the response variability associated with the anticoagulant therapy (heparins, rivaroxaban, apixaban, and dabigatran) and the potential pharmacogenes contributing to such response variability. Several genetic polymorphisms were reported as potential contributors to variances in response to anticoagulant therapy and were associated with adverse events. A link has been proposed for heparin resistance with single nucleotide polymorphisms (SNPs) of the anti-thrombin-encoding gene (SERPINC1) as well as heparin-induced thrombocytopenia with human leukocyte antigen (HLA) variant allele (HLA-DRB3*01:01). Several investigations also remarked variations in the serum drug level of direct oral anticoagulants (DOACs) that are associated with SNPs in the proteins contributing to the pharmacokinetics of the anticoagulant agent. Several studies discerned significant associations between SNPs in the ABCB1 gene and elevations in the serum levels of rivaroxaban, apixaban, and dabigatran. Moreover, carriers of the variant genotype of the SNP (rs776746) in the cytochrome P450 3A5 enzyme-encoding gene (CYP3A5) had significantly higher drug levels when compared with the non-carriers. In contrast, some SNPs were reported to impart a protective phenotype to the carrier. The SNP (rs2244613) in the carboxylesterase-encoding gene (CES1) has been significantly associated with a decline in dabigatran trough levels and a lower risk of hemorrhage. Further investigations are essential to elucidate the extent of pharmacogenetics-based alterations in the drug levels as well as the subsequent clinical outcomes of anticoagulant therapy.

Variation in Plasma Levels of Apixaban and Rivaroxaban in Clinical Routine Treatment of Venous Thromboembolism.

Direct oral anticoagulants (DOACs) apixaban and rivaroxaban are broadly used in the management of venous thromboembolism (VTE). Although not routinely required, measurement of their plasma concentration is advised for an increasing number of indications. Due to the lack of therapeutic ranges, current guidelines recommend reporting DOAC plasma levels together with expected levels from previous pivotal studies. The aim of this study was to assess DOAC level variation in a large VTE patient population. Drug concentrations determined by measurement of the anti-Xa-activity using drug-specific calibrators in citrated plasma samples from patients on rivaroxaban (n = 1471) or apixaban (n = 725) were analyzed. Observed 5th–95th percentile ranges of apixaban peak/trough levels (63–299/13–114 ng/mL for 5 mg, 37–161/7–68 ng/mL for 2.5 mg twice daily) were similar to previously reported mass-spectrometry-based reference data, and 10th–90th percentile ranges of rivaroxaban peak/trough levels (98–367/8–55 ng/mL for 20 mg, 51–211/5–27 ng/mL for 10 mg once daily) were even narrower. Age and drug levels correlated weakly (r ≤ 0.330). Drug levels measured repeatedly in subgroups of patients showed a strong correlation (r ≥ 0.773). In conclusion, anti-Xa-activity-based measurement of apixaban and rivaroxaban yields reliable results. However, the paucity of levels off-range underlines the need for evidence-based thresholds to better assist clinical decision making.

MO420: Effects of Indoxyl Sulfate and Apixaban in Liver Gene Expression

Abstract BACKGROUND AND AIMS Uraemic toxins accumulate in the blood and tissues of patients with chronic kidney disease (CKD). Previous animal studies have shown that chronic kidney disease (CKD) not only alters the elimination of drugs excreted by the kidneys, but it also impacts the metabolism of drugs subject to non-renal clearance, which involves mainly the liver and the gut. The use of apixaban, an oral anticoagulant, has been approved in the USA for dialysis patients. However, the coexistence of thrombotic and haemorrhagic risk in patients with CKD makes dose adjustment difficult. The liver has a major role in drug metabolization. Hepatocytes express high levels of AhR, a ligand-inducible transcription factor that mediates the induction of various liver cytochrome P450 enzymes by xeno and endobiotic. Tryptophan-derived uraemic toxins (TDUT) are AhR agonists. Indoxyl sulfate (IS) is the main TDUT involved in uraemic syndrome. IS increases the expression and activity of P-glycoprotein (P-gp) in the liver. Apixaban metabolism is mediated by P-gp and Cyp3a4 (Cyp3a11 in mice). We aim to study the effect of apixaban and IS in the expression of drug metabolism genes. Our hypothesis is that AhR activation by IS could severely modify drug metabolism during CKD. METHOD C57BL/6J Wild-type mice purchased from The Jackson Laboratory were fed ad libitum with a standard diet. At 10 weeks of age, mice drinking water was substituted with a 5% sucrose water solution with either 0.1% indoxyl sulphate or KCl (control) added at equivalent concentrations. 48-h before sacrifice some mice were gavaged with an apixaban solution (0.6 mg/mL) twice a day with the last dose given 4 h prior to sacrifice. All mice were sacrificed at 11 weeks of age. Liver samples were stored in an RNA-later solution at −20°C. Samples were thawed and lysed in Trizol using the Tissue-Ruptor system (Qiagen). RNA was extracted and purified with chloroform and precipitated with isopropanol. RNA concentration was estimated by spectrophotometry. Gene expression was analysed by q-RT-PCR using Gusb as a housekeeping gene. Apixaban levels were quantified by LC-MS. Kruskal–Wallis followed by a two-stage linear step-up procedure of Benjamini, Krieger and Yekutieli (q &amp;lt; 0.05) was performed using GraphPad Prism 9.2.1. RESULTS Four groups of mice per sex were thus created: WT-KCl, WT-IS, WT-KCl Apix, WT-IS Apix. In the IS/KCl model we observe higher mRNA basal expression of Abcb1a (q = 0.008) and Sult1a1 (q = 0.006) and lower basal expression of Abcg2 (q = 0.0005) in females compared to males when treated with KCl. IS treatment increases Cyp1a2 expression in females (q = 0.0139) and Cyp1a1 in both males (q = 0.0145) and females (q = 0.026). In the IS/KCl-Apix model the same sex-related differences are maintained for Abcb1a (q = 0.0031), Sult1a1 (q = 0.0316) and Abcg2 (q &amp;lt; 0.0001). In males, CYP2e1 expression is increased by apixaban in KCl (q = 0.067) and IS (q = 0.0278) treated mice. Moreover, apixaban counteracts the increased expression of Cyp1a1 induced by IS (q = 0.0177). The expression of Cyp3a11 is augmented in males treated with KCl-apixaban (q = 0.0143), an effect that seems to be reversed by IS (q = 0.0066). In females, apixaban has no effect in gene expression. Apixaban serum concentration is higher in KCl (q = 0.0350) and IS (q = 0.0019) treated females when compared to males. CONCLUSION The effect of IS as an agonist of AhR in the liver is confirmed by the increased expression of Cyp1a1. Apixaban provokes a remarkable increase of Cyp3a11 in male mice, which could lead to higher degradation rates decreasing its activity. IS seems to reverse this effect. This could lead to increased activity of apixaban during CKD which could derive in an increased risk of bleeding. Higher BCRP rates could explain lower rates of apixaban in male serum. Apixaban did not alter gene expression in females. Clinical trials in CKD are generally biased regarding sex (fewer women represented) possibly masking important sex-dependent drug adverse effects. Our results show great differences in basal expression of various genes, confirming the importance to study men and women separately with respect to drug metabolism.

Prospective cohort study on the use of low molecular weight heparin calibrated anti-Xa assay for measurement of direct oral Xa inhibitors in ex vivo patient samples

Drug-specific anti-Xa chromogenic assays are recommended for measurement of direct anti-Xa inhibitor levels but are not routinely available in many institutions. We performed a prospective study to determine: (1) the relationship between low molecular weight heparin (LMWH) calibrated anti-Xa measurements and apixaban or rivaroxaban levels measured using drug-specific anti-Xa assays and, (2) if a LMWH calibrated anti-Xa assay can be used to detect clinically significant apixaban or rivaroxaban levels. Haematology outpatients on rivaroxaban or apixaban for at least 72 h were recruited for this study. Anti-Xa LMWH assay was performed using the Innovance Heparin Anti-Xa kit/calibrator. Drug-specific levels were determined using STA-Liquid anti-Xa kit/STA-Apixaban or STA-Rivaroxaban calibrators. Serial dilutions with pooled normal plasma were performed for specimens with anti-Xa LMWH activity greater than 1.50 ng/mL to obtain anti-Xa levels within the reportable range (0.10-1.50 ng/mL) and multiplied by the dilution factor to determine actual anti-Xa level. Seventy-five (39 rivaroxaban, 36 apixaban) specimens from 67 patients (mean age 60.3 years; 53.3% males) were available for analysis. Rivaroxaban levels ranged from <25 to 500 ng/mL while apixaban levels ranged from <20 to 236.1 ng/mL. For both rivaroxaban and apixaban, there was linear and good correlation (R2= 0.96) between direct oral anticoagulants and anti-Xa LMWH levels. Using the correlation equation from our data, a rivaroxaban concentration of 50 ng/mL [International Society on Thrombosis and Haemostasis (ISTH) threshold for consideration of antidotes in bleeding patients] and 30 ng/mL (ISTH threshold for consideration of reversal agents prior to interventions), corresponds to anti-Xa LMWH levels of 0.50 and 0.35 IU/mL, respectively. For apixaban the corresponding anti-Xa LMWH levels were 0.35 and 0.20 IU/mL, respectively. In conclusion, LWWH calibrated anti-Xa assay can be used in emergency situations to screen for clinically significant apixaban or rivaroxaban levels when drug-specific calibrators are not available.

Can a Single Measurement of Apixaban Levels Identify Patients at Risk of Overexposure? A Prospective Cohort Study.

Background Patients with atrial fibrillation (AF) are frequently treated with apixaban 2.5-mg twice daily (BID) off-label, presumably to reduce the bleeding risk. However, this approach has the potential to increase the risk of ischemic stroke. If a single measurement could reliably identify patients with high drug levels, the increased stroke risk may be mitigated by confining off-label dose reduction to such patients. Objectives This study aimed to determine whether a single high apixaban level is predictive of a similarly high level when the test is repeated in 2 months. Methods In this prospective cohort study of clinic patients receiving apixaban 5-mg BID for AF or venous thromboembolism, peak and trough apixaban levels were measured using the STA-Liquid anti-Xa assay at baseline and 2 months. We calculated the proportions of patients with levels that remained in the upper quintile. Results Of 100 enrolled patients, 82 came for a second visit, 55 of whom were treated with apixaban 5-mg BID. Seven (63.6%, 95% confidence interval [CI]: 35.4–84.8%) and nine (81.8%, 95% CI: 52.3–94.9%) of 11 patients with a baseline trough and peak level in the upper quintile, respectively, had a subsequent level that remained within this range. Only one (9.1%, 95% CI: 1.6–37.7%) patient had a subsequent level that fell just lower than the median. Conclusion The trough and peak levels of apixaban in patients who have a high level on a single occasion, usually remain high when the assay is repeated in 2 months. Accordingly, the finding of a high apixaban level in patients deemed to be at high risk of bleeding, allows physicians contemplating off-label use of the 2.5-mg BID dose to limit its use to selected patients who are less likely to be exposed to an increased risk of thrombosis.