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.

Apixaban and Rivaroxaban Anti-Xa Level Monitoring Versus Standard Monitoring in Hospitalized Patients With Acute Kidney Injury.

BACKGROUND: Oral direct factor Xa inhibitors (FxaIs) are renally eliminated; thus, acute kidney injury (AKI) may increase the risk for drug accumulation and bleeding. There is minimal data describing the effects of AKI on FxaI anti-Xa levels or clinical outcomes. OBJECTIVE: To compare anti-Xa level monitoring with standard monitoring in patients who experience AKI on apixaban or rivaroxaban. METHODS: This retrospective study included patients admitted within a large hospital system from May 2016 to October 2020. Patients were included if they received apixaban or rivaroxaban prior to AKI. Patients were stratified into 1 of 2 groups: those with anti-Xa level monitoring or those who received standard monitoring. The primary outcome was major bleeding as defined by the International Society of Thrombosis and Haemostasis. RESULTS: A total of 196 patients were included in the final analysis. Major bleeding occurred in 2 patients who received anti-Xa level monitoring, compared with 14 patients who received standard monitoring (2.1% vs 14%; P < 0.01). Variables identified as predictors of major bleeding included a documented history of liver disease (adjusted odds ratio = 3.17; 95% CI = 1.04-9.67; P = 0.04) and antiplatelet use (adjusted odds ratio = 4.18; 95% CI = 1.28-13.7; P = 0.02). CONCLUSION AND RELEVANCE: This is the first study to demonstrate that anti-Xa level monitoring was associated with a significant reduction in major bleeding compared with standard monitoring in patients with AKI who received apixaban or rivaroxaban. The optimal management of antithrombotic medications in patients with AKI and recent exposure to an FxaI requires further investigation.

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.

Evaluation of the impact of body mass index on warfarin requirements in hospitalized patients.

BACKGROUND: Despite well established empiric dose adjustments for drug and disease-state interactions, the impact of body mass index (BM) on warfarin remains unclear. The objective of this study is to evaluate warfarin requirements in hospitalized patients, stratified by BMI. METHODS: This retrospective review included two cohorts of patients: cohort A (patients admitted with a therapeutic international normalized ratio (INR)) and cohort B (newly initiated on warfarin during hospitalization). Exclusion criteria included: age under 18 years, pregnancy, INR (goal 2.5-3.5), and warfarin thromboprophylaxis post orthopedic surgery. The primary outcome was mean total weekly dose (TWD) of warfarin based on weight classification: underweight (BMI <18 kg/m2), normal/overweight (BMI 18-29.9 kg/m2), obese (BMI 30-39.9 kg/m2), and morbidly obese (BMI ⩾ 40 kg/m2). Data were extracted from two community hospitals in reverse chronologic order during July 2015-June 2013 until both study institutions evaluated 100 patients per cohort in each BMI classification or until all patients had been evaluated within the prespecified timeframe. RESULTS: A total of 585 patients were included in cohort A (26 underweight, 200 normal/overweight, 200 obese, 159 morbidly obese). There was a statistically significant difference in TWD as determined by one-way analysis of variance ( p < 0.05). A Tukey post hoc test revealed a statistically significantly higher TWD in morbidly obese (41.5 mg) compared with underweight (25.6 mg, p < 0.05), normal/overweight (28.8 mg, p < 0.05) and obese patients (32.4 mg, p < 0.05). In cohort B, 379 patients were evaluated (9 underweight, 166 normal/overweight, 152 obese, 52 morbidly obese). Overall, 191 patients had a therapeutic INR on discharge (88.9% underweight, 52.4% normal/overweight, 44.1% obese, 55.8% morbidly obese, p = 0.035). Of those, there was a statistically significant difference in TWD ( p = 0.021) with a higher TWD in the morbidly obese (41 mg) compared with underweight patients (24.4 mg, p = 0.017). CONCLUSIONS: Based on the results of this study, morbidly obese patients may require higher TWD to obtain and maintain a therapeutic INR.