The Relationship between Anti-Factor Xa Level and Clinical Outcome in Patients Receiving Enoxaparine Low Molecular Weight Heparin to Prevent Deep Vein Thrombosis after Hip Replacement

A systematic review of therapeutic enoxaparin dosing in obesity

Enoxaparin is a hydrophilic drug with obesity having little effect on its apparent volume of distribution, therefore patients with obesity receiving standard 1 mg/kg dosing may be at a higher risk of supratherapeutic dosing. Conversely, dose reducing patients with obesity could place already at risk patients at higher risk of a thrombotic event. Data and recommendations are variable for the most appropriate weight-based dose of therapeutic enoxaparin in obese patients, particularly those a weight > 100 kg or a body mass index (BMI) ≥ 40 kg/m2. The purpose of this systematic review was to globally evaluate these data to surmise optimal dosing recommendations for patients with obesity. A systematic review of English language studies was conducted and identified articles via Pubmed, EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL) searches. Studies were included if they reported therapeutic enoxaparin use in adult patients with a BMI ≥ 40 kg/m2 or body weight > 100 kg and the percentage of patients achieving a therapeutic anti-Xa based on a weight-based dose or the weight-based dose required to produce a therapeutic anti-Xa level. Therapeutic attainment of anti-Xa levels were assessed across enoxaparin weight-based dosing categories including a very low dose group: < 0.75 mg/kg, low dose group: 0.75-0.85 mg/kg, and standard dose group: ≥ 0.95 mg/kg. Rates of bleeding and thrombosis were also evaluated. A total of eight studies were included. For anti-Xa level assessment, 682 patients were included. A total of 62% of anti-Xa levels were therapeutic in the very low dose group, 66% in the low dose group, and 42% in the standard dose group. Overall rates of total bleeding and thrombosis were assessed in 798 patients. A total of 29 bleedings (3.6%) occurred, and 27 reported a relationship to dose. Most bleedings, 85.2% (n = 23/27), occurred with doses in the standard dose group (≥ 0.95 mg/kg). Thrombosis occurred in 5 patients (0.6%). Utilization of a reduced weight-based dosing strategy for therapeutic enoxaparin in obese patients may increase the percentage of patients with a therapeutic anti-Xa level.

Being precise with anticoagulation to reduce adverse drug reactions: are we there yet?

Anticoagulants are potent therapeutics widely used in medical and surgical settings, and the amount spent on anticoagulation is rising. Although warfarin remains a widely prescribed oral anticoagulant, prescriptions of direct oral anticoagulants (DOACs) have increased rapidly. Heparin-based parenteral anticoagulants include both unfractionated and low molecular weight heparins (LMWHs). In clinical practice, anticoagulants are generally well tolerated, although interindividual variability in response is apparent. This variability in anticoagulant response can lead to serious incident thrombosis, haemorrhage and off-target adverse reactions such as heparin-induced thrombocytopaenia (HIT). This review seeks to highlight the genetic, environmental and clinical factors associated with variability in anticoagulant response, and review the current evidence base for tailoring the drug, dose, and/or monitoring decisions to identified patient subgroups to improve anticoagulant safety. Areas that would benefit from further research are also identified. Validated variants in VKORC1, CYP2C9 and CYP4F2 constitute biomarkers for differential warfarin response and genotype-informed warfarin dosing has been shown to reduce adverse clinical events. Polymorphisms in CES1 appear relevant to dabigatran exposure but the genetic studies focusing on clinical outcomes such as bleeding are sparse. The influence of body weight on LMWH response merits further attention, as does the relationship between anti-Xa levels and clinical outcomes. Ultimately, safe and effective anticoagulation requires both a deeper parsing of factors contributing to variable response, and further prospective studies to determine optimal therapeutic strategies in identified higher risk subgroups.

Monitoring anti-Xa Levels to Optimize Low-Molecular-Weight-Heparin Thromboprophylaxis in High-Risk Hospitalized Patients: A Stratified Meta-Analysis

It is uncertain whether monitoring or targeting anti-Xa levels is necessary when using low-molecular-weight-heparin (LMWH) to prevent venous thromboembolism (VTE). This stratified meta-analysis assessed whether monitoring trough or peak anti-Xa levels with LMWH dosing would reduce risk of VTE. Twelve non-randomized studies involving 3604 hospitalized patients met the inclusion criteria and were subject to meta-analysis. Eight studies assessed the association between VTE and peak anti-Xa levels (between .2 and .5 IU/ml) and four studies assessed the benefits of targeting the trough anti-Xa levels (>.1 IU/ml). Achieving an adequate peak or trough anti-Xa level was associated with a reduced risk of VTE (random-effects model odds ratio [OR] .52, 95% confidence interval [CI] .34-.77; P = .001, I2 = 30% and P-value for heterogeneity = .171) compared with using a fixed standard dose of LMWH. Targeting the trough level (OR .40, 95%CI 0.22-.75, P = .004) appeared to be more effective than targeting the peak level (OR .62, 95%CI 0.37-1.03, P = .066), although a formal interaction analysis did not confirm they were statistically different (ratio of ORs = 1.52, 95%CI 0.68-3.40; z score = 1.03, P = .306). Targeting a higher anti-Xa level did not appear to increase the risk of bleeding or transfusion (OR 1.20, 95%CI 0.46-3.17, P = .707).

Evaluating residual anti-Xa levels following discontinuation of treatment-dose enoxaparin in patients presenting for elective surgery: a prospective observational trial

INTRODUCTION

Prior studies have demonstrated that patients presenting for elective surgery may have higher-than-expected residual anti-Xa level activity at or beyond 24 hours following their last treatment dose of enoxaparin. Given that 24 hours of abstinence is currently recommended by both European and American societies before the performance of neuraxial or deep anesthetic/analgesic procedures, determining the actual timeframe at which residual anti-Xa level activity reliably falls below 0.2 IU/mL, the lower limit of the target range for thromboprophylaxis, is critical.

METHODS

This was a prospective observational trial. Consenting patients on treatment-dose enoxaparin were randomized to either a 24-hour group (last dose at 07:00 the day prior to surgery) or a 36-hour group (last dose at 19:00 2 days prior to surgery). On arrival for surgery, blood samples were obtained to assess residual anti-Xa level activity and renal function. The primary outcome was residual anti-Xa level activity following the last treatment dose of enoxaparin. Incorporating all patients, linear regression modeling was performed to predict the timepoint at which the level of anti-Xa activity reliably fell below 0.2 IU/mL.

RESULTS

103 patients were analyzed. Time from the last dose at which residual anti-Xa activity fell below 0.2 IU/mL, based on the upper bound of the 95% CI, was 31.5 hours. No correlation overall between age, renal function, or sex was found.

CONCLUSION

Residual levels of anti-Xa activity do not reliably fall below 0.2 IU/mL 24 hours following discontinuation of treatment-dose enoxaparin. Therefore, current time-based guidelines are not conservative enough. Routine anti-Xa testing should be strongly considered, or current time-based guidelines should be reassessed.

TRIAL REGISTRATION NUMBER

NCT03296033.

Is There a Role for Anti-factor Xa Activity Assay in Venous Thromboembolism Prophylaxis Management Among Orthopaedic Trauma Patients? Systematic Review and Meta-analysis

OBJECTIVES

To determine the effect of anti-factor Xa assay dosing of low-molecular-weight heparin (LMWH) on rates of venous thromboembolism (VTE), deep vein thrombosis (DVT), pulmonary embolism (PE), bleeding, and mortality among orthopaedic trauma patients.

DATA SOURCES

PubMed/MEDLINE, Embase, Ovid, Cochrane Central Register of Controlled Trials (CENTRAL), clinicaltrials.gov , and Scopus were systematically searched from inception of the database to 2021.

STUDY SELECTION

Prospective, retrospective, and randomized controlled trial studies were included if they compared rates of VTE, DVT, PE, bleeding, and/or mortality between orthopaedic trauma patients receiving anti-factor Xa-based LMWH dosing and those receiving standard dosing.

DATA EXTRACTION

Two independent reviewers screened titles and abstracts for eligibility. Study characteristics including study design, inclusion criteria, and intervention were extracted.

DATA SYNTHESIS

Meta-analysis was performed using pooled proportion of events (effect size) with 95% confidence intervals. A random-effects model was used. Heterogeneity was quantified by Higgins I 2 . Heterogeneity and variability between subgroups indicated differences in the pooled estimate represented by a P -value.

RESULTS

Six hundred eighty-five studies were identified, and 10 studies including 2870 patients were included. In total, 30.3% and 69.7% received an adjusted and nonadjusted dose of LMWH, respectively. The rate of VTE and DVT were significantly lower in the anti-factor Xa-adjusted cohort, whereas there was no statistically significant difference in rates of PE, bleeding, or mortality between the cohorts.

CONCLUSIONS

This systematic review and meta-analysis demonstrates that anti-factor Xa activity assay dosing of LMWH among orthopaedic trauma patients leads to a reduction in overall DVT rates, although not PE rates, without an increased risk of bleeding events.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

The Impact of Continuous Veno-Venous Hemodiafiltration on the Efficacy of Administration of Prophylactic Doses of Enoxaparin: A Prospective Observational Study

BACKGROUND

Critically ill patients frequently require continuous renal replacement therapy (CRRT). During CRRT, particles up to 10 kDa in size, such as enoxaparin, may be removed. The aim of this study was to determine if patients receiving prophylactic doses of enoxaparin and treated with continuous veno-venous hemodiafiltration (CVVHDF) reach prophylactic values of anti-Xa factor activity.

METHODS

In this observational trial, we compared two groups: 20 patients treated with CVVHDF and 20 patients not treated with CVVHDF. All of them received prophylactic doses of 40 mg of enoxaparin subcutaneously. Anti-Xa factor activity was determined on the third day of receiving a prophylactic dose of enoxaparin. The first blood sample was taken just before the administration of enoxaparin, and other samples were taken 3 h, 6 h, and 9 h after the administration of a prophylactic dose of enoxaparin.

RESULTS

At 3 and 6 h after administration of enoxaparin in both groups, we observed a significant increase in anti-Xa factor activity from baseline, with the peak after 3 h of administration. There were no significant differences in the numbers of patients who had anti-Xa factor activity within the prophylactic range between CVVHDF and control groups.

CONCLUSION

CVVHDF has only a mild effect on the enoxaparin prophylactic effect measured by anti-Xa factor activity. Thus, it seems there is no need to increase the dose of enoxaparin for patients requiring CVVHDF.

Population Pharmacokinetics and Probability of Target Attainment Analysis of Nadroparin in Different Stages of COVID-19

BACKGROUND AND OBJECTIVE

The risk of thrombotic complications in critical patients with COVID-19 remains extremely high, and multicenter trials failed to prove a survival benefit of escalated doses of low-molecular-weight heparins (nadroparin calcium) in this group. The aim of this study was to develop a pharmacokinetic model of nadroparin according to different stages of COVID-19 severity.

METHODS

Blood samples were obtained from 43 patients with COVID-19 who received nadroparin and were treated with conventional oxygen therapy, mechanical ventilation, and extracorporeal membrane oxygenation. We recorded clinical, biochemical, and hemodynamic variables during 72 h of treatment. The analyzed data comprised 782 serum nadroparin concentrations and 219 anti-Xa levels. We conducted population nonlinear mixed-effects modeling (NONMEM) and performed Monte Carlo simulations of the probability of target attainment for reaching 0.2-0.5 IU/mL anti-Xa levels in study groups.

RESULTS

We successfully developed a one-compartment model to describe the population pharmacokinetics of nadroparin in different stages of COVID-19. The absorption rate constant of nadroparin was 3.8 and 3.2 times lower, concentration clearance was 2.22 and 2.93 times higher, and anti-Xa clearance was 0.87 and 1.1 times higher in mechanically ventilated patients and the extracorporeal membrane oxygenation group compared with patients treated with conventional oxygen, respectively. The newly developed model indicated that 5.900 IU of nadroparin given subcutaneously twice daily in the mechanically ventilated patients led to a similar probability of target attainment of 90% as 5.900 IU of subcutaneous nadroparin given once daily in the group supplemented with conventional oxygen.

CONCLUSIONS

Different nadroparin dosing is required for patients undergoing mechanical ventilation and extracorporeal membrane oxygenation to achieve the same targets as those for non-critically ill patients.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier no. NCT05621915.

Residual anti-Xa activity in plasma of patients presenting for electively planned neuraxial regional anesthesia

OBJECTIVE

To determine the incidence of increased anti-Xa activity within plasma levels 24 hours after administration of therapeutic dose low-molecular-weight heparin in patients presenting for elective neuraxial anesthesia.

BACKGROUND

Guidelines for neuroaxial regional anesthesia for patients with antithrombotic drugs recommend time intervals for waiting. There is scientific evidence to suggest that the recommended interval of 24 hours may be insufficient in patients treated with therapeutic dose low-molecular-weight heparin.

METHODS

Retrospective cohort analysis of 74 patients who received therapeutic dose low-molecular-weight heparin before planned neuraxial anesthesia between April 1, 2015 and April 1, 2020 at Freiburg University Hospital. Primary endpoint was the occurrence of elevated plasma anti-Xa levels in prophylactic range or higher (>0.2 IU/mL) 24 hours after the last application of the therapeutic dose.

RESULTS

24 hours after the last dose of therapeutic low-molecular-weight heparin, 18.0% of patients had elevated anti-Xa activity levels >0.2 IU/mL. A weak correlation between the time since the last administration of low-molecular-weight heparin and plasma anti-Xa levels could be found. No other risk factors were seen.

CONCLUSIONS

Relevant residual anticoagulant activity, as measured by plasma anti-Xa levels within a prophylactic range, is measurable 24 hours after the last administration of therapeutic dose low-molecular-weight heparin.

TRIAL REGISTRATION NUMBER

German Clinical Trials Register DRKS00022099.

Efficacy and Safety of Two Different Enoxaparin Doses for Thromboprophylaxis in Non-critically Ill Patients: A Randomized Controlled Trial

Background

Recently, a few studies based on anti-factor Xa activity levels have propounded doubtful and sub-prophylactic levels by the usual dose of enoxaparin in surgical and critically ill patients. In this study, we assessed two doses of enoxaparin in adult non-critically ill patients.

Methods

Patients were randomly assigned into two groups of intervention and control. While the intervention group received enoxaparin with a daily dose of 60 mg, the control group received enoxaparin 40 mg. Anti-factor Xa activity was measured based on the peak steady-state levels. The level of 0.2 to 0.4 IU/mL was considered as a prophylactic goal. All individuals were followed for bleeding or thromboembolic events during admission.

Results

The mean levels of anti-factor Xa were 0.29 ± 0.13 IU/mL in the control group (n = 31) and 0.44 ± 0.19 IU/mL in the intervention group (n = 29). More patients in the control group had an optimal level of anti-factor Xa compared to the patients in the intervention group (62.1% vs. 29%). No adverse outcomes were detected in any of the groups.

Conclusions

Enoxaparin dose of 60 mg daily provided anti-factor Xa level higher than desired in most patients. In non-critically ill patients, the dose of 40 mg is the proper dose for thromboprophylaxis.

Low Anti-Factor Xa Level Predicts 90-Day Symptomatic Venous Thromboembolism in Surgical Patients Receiving Enoxaparin Prophylaxis: A Pooled Analysis of Eight Clinical Trials

OBJECTIVE

To examine the relationship between enoxaparin dose adequacy, quantified with anti-Factor Xa (aFXa) levels, and 90-day symptomatic venous thromboembolism (VTE) and postoperative bleeding.

SUMMARY BACKGROUND DATA

Surgical patients often develop "breakthrough" VTE events-those which occur despite receiving chemical anticoagulation. We hypothesize that surgical patients with low aFXa levels will be more likely to develop 90-day VTE, and those with high aFXa will be more likely to bleed.

METHODS

Pooled analysis of eight clinical trials (N = 985) from a single institution over a 4 year period. Patients had peak steady state aFXa levels in response to a known initial enoxaparin dose, and were followed for 90 days. Survival analysis log-rank test examined associations between aFXa level category and 90-day symptomatic VTE and bleeding.

RESULTS

Among 985 patients, 2.3% (n = 23) had symptomatic 90-day VTE, 4.2% (n = 41) had 90-day clinically relevant bleeding, and 2.1% (n = 21) had major bleeding. Patients with initial low aFXa were significantly more likely to have 90-day VTE than patients with adequate or high aFXa (4.2% vs 1.3%, P = 0.007). In a stratified analysis, this relationship was significant for patients who received twice daily (6.2% vs 1.5%, P = 0.003), but not once daily (3.0% vs 0.7%, P = 0.10) enoxaparin. No association was seen between high aFXa and 90-day clinically relevant bleeding (4.8% vs 2.9%, P = 0.34) or major bleeding (3.6% vs 1.6%, P = 0.18).

CONCLUSIONS

This manuscript establishes inadequate enoxaparin dosing as a plausible mechanism for breakthrough VTE in surgical patients, and identifies anticoagulant dose adequacy as a novel target for process improvement measures.

THE EFFICACY OF WEIGHT-BASED ENOXAPARIN DOSING FOR VTE-PROPHYLAXIS IN TRAUMA PATIENTS: A SYSTEMATIC REVIEW AND META-ANALYSIS

BACKGROUND

Trauma patients are at high risk of developing venous thromboembolism (VTE), and standard dosing enoxaparin regimens may be inadequate for prophylaxis. This meta-analysis was performed to clarify the efficacy of alternative dosing regimens for VTE prophylaxis in this high-risk group. The objective of this systematic review was to review the evidence regarding weight-based dosing of enoxaparin for VTE prophylaxis in trauma patients.

METHODS

A systematic database search was undertaken for studies comparing standard vs weight-based dosing of enoxaparin for VTE prophylaxis in adult trauma patients, aged ≥18 years. The primary outcome was the achievement of Anti-Factor Xa (AFXa) levels within the prophylactic range. Secondary outcomes included: sub-prophylactic AFXa levels, supra-prophylactic AFXa levels, VTE incidence and bleeding events. Meta-analysis was conducted using both fixed- and random-effects models, and presented as odds ratios (OR), risk ratios (RR) and risk differences (RD) with 95% confidence intervals (CI).

RESULTS

Four cohort studies were eligible for inclusion. Compared to standard dosing, weight-based enoxaparin prophylaxis dosing was associated with increased odds of prophylactic AFXa levels (OR = 5.85., 95%CI: 3.02-11.30, p < 0.00001) and reduced risk of sub-prophylactic AFXa levels (RR = 3.97, 95%CI: 3.02-5.22, p < 0.00001). Standard dosing was associated with a reduced risk of supra-therapeutic AFXa levels (RR = 0.23, 95%CI: 0.11-0.50, P = 0.0002), but this was not associated with a difference in risk of bleeding events (RD = -0.00, 95%CI: -0.02-0.01, P = 0.55). There was no statistical difference in incidence VTE between the two groups (RD = 0.01, 95%CI: -0.02-0.03, P = 0.64).

CONCLUSIONS

Compared with standard dosing, weight-based enoxaparin dosing regimens are associated with increased odds of prophylactic range AFXa levels. Further investigation is required to determine if this translates into improved VTE prophylaxis and reduced VTE incidence.

LEVEL OF EVIDENCE

Systematic Review, level III.

Anti-factor Xa Activity Is Not Associated With Venous Thromboembolism in Critically Ill Patients Receiving Enoxaparin for Thromboprophylaxis: A Retrospective Observational Study

Background

Anti-factor Xa activity has been suggested as a surrogate parameter for judging the effectiveness of pharmacological thromboprophylaxis with low molecular weight heparins in critically ill patients. However, this practice is not supported by evidence associating low anti-factor Xa activity with venous thromboembolism.

Methods

We performed a retrospective observational study including 1,352 critically ill patients admitted to 6 intensive care units of the Medical University of Vienna, Austria between 01/2015 and 12/2018. Included patients received prophylactically dosed enoxaparin (≤100 IU/kg body weight per day). We analyzed median peak, 12-h trough and 24-h trough anti-factor Xa activity per patient and compared anti-factor Xa activity between patients without vs. with venous thromboembolic events.

Results

19 patients (1.4%) developed a total of 22 venous thromboembolic events. We did not observe a difference of median (IQR) anti-factor Xa activity between patients without venous thromboembolism [peak 0.22 IU/mL (0.14–0.32); 12-h trough 0.1 IU/mL (<0.1–0.17), 24-h trough < 0.1 IU/mL (<0.1– <0.1)] vs. patients with venous thromboembolism [peak 0.33 IU/mL (0.14–0.34); 12-h trough 0.12 IU/mL (<0.1–0.26); 24-h trough < 0.1 IU/mL (<0.1–<0.1)].

Conclusion

Patients who developed venous thromboembolism had anti-factor Xa activities comparable to those who did not suffer from venous thromboembolism.

Regional anaesthesia in patients on antithrombotic drugs: Joint ESAIC/ESRA guidelines

BACKGROUND

Bleeding is a potential complication after neuraxial and peripheral nerve blocks. The risk is increased in patients on antiplatelet and anticoagulant drugs. This joint guideline from the European Society of Anaesthesiology and Intensive Care and the European Society of Regional Anaesthesia aims to provide an evidence-based set of recommendations and suggestions on how to reduce the risk of antithrombotic drug-induced haematoma formation related to the practice of regional anaesthesia and analgesia.

DESIGN

A systematic literature search was performed, examining seven drug comparators and 10 types of clinical intervention with the outcome being peripheral and neuraxial haematoma. Grading of Recommendations, Assessment, Development and Evaluation (GRADE) was used for assessing the methodological quality of the included studies and for formulating recommendations. A Delphi process was used to prepare a clinical practice guideline.

RESULTS

Clinical studies were limited in number and quality and the certainty of evidence was assessed to be GRADE C throughout. Forty clinical practice statements were formulated. Using the Delphi-process, strong consensus (>90% agreement) was achieved in 57.5% of recommendations and consensus (75 to 90% agreement) in 42.5%.

DISCUSSION

Specific time intervals should be observed concerning the adminstration of antithrombotic drugs both prior to, and after, neuraxial procedures or those peripheral nerve blocks with higher bleeding risk (deep, noncompressible). These time intervals vary according to the type and dose of anticoagulant drugs, renal function and whether a traumatic puncture has occured. Drug measurements may be used to guide certain time intervals, whilst specific reversal for vitamin K antagonists and dabigatran may also influence these. Ultrasound guidance, drug combinations and bleeding risk scores do not modify the time intervals. In peripheral nerve blocks with low bleeding risk (superficial, compressible), these time intervals do not apply.

CONCLUSION

In patients taking antiplatelet or anticoagulant medications, practitioners must consider the bleeding risk both before and after nerve blockade and during insertion or removal of a catheter. Healthcare teams managing such patients must be aware of the risk and be competent in detecting and managing any possible haematomas.

Optimising the Nadroparin Dose for Thromboprophylaxis During Hemodialysis by Developing a Population Pharmacodynamic Model Using Anti-Xa Levels

INTRODUCTION

The optimal nadroparin dose in patients undergoing hemodialysis is difficult to determine in clinical practice. Anti-Xa levels ≥ 0.4 IU/mL and < 2.0 IU/mL are suggested to prevent thrombus formation within the extracorporeal circuit whilst minimizing bleeding risk. We aimed to characterize the variability in the association between dose and anti-Xa levels, identify patient and dialysis characteristics that explained this variability, and optimize nadroparin dosing based on the identified characteristics.

METHODS

Anti-Xa samples were collected in patients who received intravenous nadroparin as thromboprophylaxis during routine dialysis sessions. A population pharmacodynamic model was developed using non-linear mixed-effects modelling. The percentage of patients ≥ 0.4 IU/mL (efficacy) and < 2.0 IU/mL (safety) was simulated for different doses, patient and dialysis characteristics.

RESULTS

Patients (n = 137) were predominantly receiving standard hemodialysis (84.7% vs. hemodiafiltration 15.3%) and had a mean bodyweight of 76.3 kg (± 16.9). Lean body mass (LBM), mode of dialysis, and dialyzer partially explained between-subject variability in anti-Xa levels. Patients on hemodiafiltration and those receiving hemodialysis with a high LBM (≥ 80 kg) had a low probability (< 29%) of anti-Xa levels ≥ 0.4 IU/mL during the entire dialysis session. All patients, except hemodialysis patients with a low LBM (< 50 kg), had a high probability (> 70%) of peak anti-Xa levels < 2.0 IU/mL.

CONCLUSION

Mainly patients receiving hemodiafiltration and those receiving hemodialysis with a high LBM can benefit from a higher nadroparin dose than currently used in clinical practice, while having anti-Xa levels < 2.0 IU/mL.

Heparin resistance in severe thermal injury: A prospective cohort study

BACKGROUND

Low molecular-weight heparin (LMWH) is routinely administered to burn patients for thromboprophylaxis. Some studies have reported heparin resistance, yet the mechanism(s) and prevalence have not been systematically studied. We hypothesized that nucleosomes, composed of histone structures with associated DNA released from injured tissue and activated immune cells in the form of neutrophil extracellular traps (NETs or NETosis), neutralize LMWH resulting in suboptimal anticoagulation, assessed by reduction in anti-factor Xa activity.

METHODS

Blood was sampled from >15% total body surface area (TBSA) burn patients receiving LMWH on days 5, 10 and 14. Peak anti-factor Xa (AFXa) activity, anti-thrombin (ATIII) activity, cell-free DNA (cfDNA) levels and nucleosome levels were measured. Mixed effects regression was adjusted for multiple confounders, including injury severity and ATIII activity, and was used to test the association between nucleosomes and AFXa.

RESULTS

A total of 30 patients with severe burns were included. Mean TBSA 43% (SD 17). Twenty-three (77%) patients were affected by heparin resistance (defined by AFXa activity <0.2 IU/mL). Mean peak AFXa activity across samples was 0.18 IU/mL (SD 0.11). Mean ATIII was 81.9% activity (SD 20.4). Samples taken at higher LWMH doses were found to have significantly increased AFXa activity, though the effect was not observed at all doses, at 8000 IU no samples were heparin resistant. Nucleosome levels were negatively correlated with AFXa (r = -0.29, p = 0.050) consistent with the hypothesis. The final model, with peak AFXa as the response variable, was adjusted for nucleosome levels (p = 0.0453), ATIII activity (p = 0.0053), LMWH dose pre-sample (p = 0.0049), drug given (enoxaparin or tinzaparin) (p = 0.03), and other confounders including severity of injury, age, gender, time point of sample.

CONCLUSIONS

Heparin resistance is a prevalent issue in severe burns. Nucleosome levels were increased post-burn, and showed an inverse association with AFXa consistent with the hypothesis that they may interfere with the anticoagulant effect of heparin in vivo and contribute to heparin resistance. Accurate monitoring of AFXa activity with appropriate therapy escalation plans are recommended with dose adjustment following severe burn injury.

Optimal Dosing of Prophylactic Enoxaparin after Surgical Procedures: Results of the Double-Blind, Randomized, Controlled FIxed or Variable Enoxaparin (FIVE) Trial

BACKGROUND

The accepted "one-size-fits-all" dose strategy for prophylactic enoxaparin may not optimize the medication's risks and benefits after surgical procedures. The authors hypothesized that weight-based administration might improve the pharmacokinetics of prophylactic enoxaparin when compared to fixed-dose administration.

METHODS

The FIxed or Variable Enoxaparin (FIVE) trial was a randomized, double-blind trial that compared the pharmacokinetic and clinical outcomes of patients assigned randomly to postoperative venous thromboembolism prophylaxis using enoxaparin 40 mg twice daily or enoxaparin 0.5 mg/kg twice daily. Patients were randomized after surgery and received the first enoxaparin dose at 8 hours after surgery. Primary hypotheses were (1) weight-based administration is noninferior to a fixed dose for avoiding underanticoagulation (anti-factor Xa <0.2 IU/ml) and (2) weight-based administration is superior to fixed-dose administration for avoiding overanticoagulation (anti-factor Xa >0.4 IU/ml). Secondary endpoints were 90-day venous thromboembolism and bleeding.

RESULTS

In total, 295 patients were randomized, with 151 assigned to fixed-dose and 144 to weight-based administration of enoxaparin. For avoidance of under anticoagulation, weight-based administration had a greater effectiveness (79.9 percent versus 76.6 percent); the 3.3 percent (95 percent CI, -7.5 to 12.5 percent) greater effectiveness achieved statistically significant noninferiority relative to the a priori specified -12 percent noninferiority margin (p = 0.004). For avoidance of overanticoagulation, weight-based enoxaparin administration was superior to fixed-dose administration (90.6 percent versus 82.2 percent); the 8.4 percent (95 percent CI, 0.1 to 16.6 percent) greater effectiveness showed significant safety superiority (p = 0.046). Ninety-day venous thromboembolism and major bleeding were not different between fixed-dose and weight-based cohorts (0.66 percent versus 0.69 percent, p = 0.98; 3.3 percent versus 4.2 percent, p = 0.72, respectively).

CONCLUSION

Weight-based administration showed superior pharmacokinetics for avoidance of underanticoagulation and overanticoagulation in postoperative patients receiving prophylactic enoxaparin.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, I.

Pharmacokinetics of enoxaparin in COVID-19 critically ill patients

Background

In intensive-care unit (ICU) patients, pathophysiological changes may affect the pharmacokinetics of enoxaparin and result in underdosing.

Objectives

To develop a pharmacokinetic model of enoxaparin to predict the time-exposure profiles of various thromboprophylactic regimens in COVID-19 ICU-patients.

Methods

This was a retrospective study in ICUs of two French hospitals. Anti-Xa activities from consecutive patients with laboratory-confirmed SARS-CoV-2 infection treated with enoxaparin for the prevention or the treatment of venous thrombosis were used to develop a population pharmacokinetic model using non-linear mixed effects techniques. Monte Carlo simulations were then performed to predict enoxaparin exposure at steady-state after three days of administration.

Results

A total of 391 anti-Xa samples were measured in 95 patients. A one-compartment model with first-order kinetics best fitted the data. The covariate analysis showed that enoxaparin clearance (typical value 1.1 L.h-1) was related to renal function estimated by the CKD-EPI formula and volume of distribution (typical value 17.9 L) to actual body weight.

Simulation of anti-Xa activities with enoxaparin 40 mg qd indicated that 64% of the patients had peak levels within the range 0.2 to 0.5 IU.mL-1 and 75% had 12-hour levels above 0.1 IU.mL-1. Administration of a total daily dose of at least 60 mg per day improved the probability of target attainment.

Conclusion

In ICU COVID-19 patients, exposure to enoxaparin is reduced due to an increase in the volume of distribution and clearance. Consequently, enoxaparin 40 mg qd is suboptimal to attain thromboprophylactic anti-Xa levels.

Impact of Weight on Anti-Xa Attainment in High-Risk Trauma Patients on Enoxaparin Chemoprophylaxis

BACKGROUND

Serum anti-factor Xa (anti-Xa) concentration may guide low molecular weight heparin chemoprophylaxis in trauma patients. Higher total body weight (TBW) is a risk factor for subprophylactic anti-Xa and venous thromboembolism (VTE). The purpose of this study was to evaluate TBW differences in patients with subprophylactic versus prophylactic trough anti-Xa.

METHODS

This retrospective study included adults admitted to the trauma service who received enoxaparin chemoprophylaxis, trough anti-Xa assessment, and screening duplex ultrasound. Initial enoxaparin dose was determined per trauma team weight-tiered protocol with subsequent 10 mg increase if anti-Xa was subprophylactic. Patients were stratified into subprophylactic (anti-Xa <0.1 IU/ml) and prophylactic (anti-Xa ≥0.1 IU/mL) groups. The primary outcome was difference in TBW. Secondary outcomes were weight-adjusted enoxaparin dose (mg/kg), VTE, red blood cell (pRBC) transfusions.

RESULTS

A total of 887 patients were included with 681 (76.8%) having subprophylactic anti-Xa. The subprophylactic group had significantly younger age, higher proportion male sex, higher Injury Severity Score (ISS), higher BMI, and longer length of hospital stay. The subprophylactic group had higher TBW (median [IQR], 87.8 [74-102] kg vs. 78.9 [68-91.8] kg; P < 0.001) which equated to a lower weight-adjusted dose (0.34 [0.3-0.41] mg/kg vs. 0.38 (0.33-0.44) mg/kg; P < 0.001). There were no differences in VTE (10.4% vs. 9.2%; P = 0.71) or pRBC administration (17.0% vs. 16.0%; P = 0.81).

CONCLUSIONS

TBW is higher and weight-adjusted enoxaparin dose is lower in high-risk trauma patients with subprophylactic anti-Xa concentrations. These data suggest TBW should be considered when determining the optimal prophylactic enoxaparin dose in high-risk trauma patients.

A fixed dose approach to thrombosis chemoprophylaxis may be inadequate in heavier critically ill patients

Objectives: Overweight patients are at greater risk of venous thromboembolism. We aimed to describe prescribing patterns of thrombosis chemoprophylaxis in critically ill patients weighing ≥ 100 kg and quantify the effectiveness of these regimens using the surrogate biomarker of plasma anti-Xa level. Design, setting and patients: A prospective single-centre cohort study was conducted over a 6-month period. Patients weighing ≥ 100 kg who were prescribed enoxaparin for chemoprophylaxis and expected to remain in the intensive care unit for > 48 hours were eligible. Anti-Xa levels were measured once a patient had received at least three consecutive doses of enoxaparin. Peak levels were measured 4-6 hours after the third dose and trough levels were measured before the fourth dose. Anti-Xa levels were compared with established target ranges for peak and trough anti-Xa levels (0.2-0.5 IU/mL and > 0.1 IU/mL, respectively). Results: Eighty-eight patients met the eligibility criteria, and anti-Xa levels for 42 patients were obtained. Fixed dose chemoprophylaxis approaches varied considerably, with 40 mg once daily (54/88 [61%]) and 40 mg twice daily (20/88 [23%]) being the most frequently prescribed regimens. No patient had a peak anti-Xa level > 0.5 IU/mL. When comparing 40 mg once daily versus twice daily, the once daily regimen had lower median trough levels (0.01 IU/mL [interquartile range (IQR), 0.00-0.04] v 0.09 IU/mL [IQR, 0.05-0.13]; P < 0.001) and greater proportions of patients with levels below the established range (< 0.1 IU/mL) (15/16 [95%] v 7/14 [50%]; P = 0.002) and levels that were undetectable (0.00 IU/mL) (8/16 [50%] v 1/14 [7%]; P = 0.01). Conclusions: At a single centre, thrombosis chemoprophylaxis prescribing patterns for heavier critically ill patients varied considerably. Current fixed dose approaches may be inadequate in this cohort.

Venous Thromboembolism Chemoprophylaxis in Burn Patients: A Literature Review and Single-Institution Experience

Hospitalized burn patients meet the criteria for Virchow's triad (endothelial damage, hypercoagulability, and stasis), predisposing them to venous thromboembolism (VTE). Although the disease burden of VTE suggests a need for prevention in this population, unreliable reported VTE rates, costly and complicated prophylaxis regimens, and chemoprophylaxis risks have prevented the establishment of a universal protocol. This paper reviews thromboprophylaxis practices both in the literature and at our own institution. A systematic review was conducted according to PRISMA guidelines identifying studies pertaining to VTE chemoprophylaxis in burn patients. Additionally, medical records of patients admitted to an American Burn Association-verified burn center between June 2015 and June 2019 were retrospectively reviewed for demographics, chemoprophylaxis, and presence of VTE defined as either deep vein thrombosis (DVT) or pulmonary embolism (PE). Thirty-eight studies met inclusion criteria. In the 12 studies that reported VTE incidence, rates ranged widely from 0.25% to 47.1%. The two largest retrospective studies (n = 33,637 and 36,638) reported a VTE incidence of 0.61% and 0.8% in populations with unknown or inconsistently recorded chemoprophylaxis. Throughout the literature, prevention protocols were mixed, though a trend toward using dose-adjusted subcutaneous low molecular weight heparin based on serum anti-factor Xa level was noted. At our burn center, 1,068 patients met study criteria. At-risk patients received a simple chemoprophylaxis regimen of 5000U of subcutaneous unfractionated heparin every 8 hours. No routine monitoring tests were performed to limit cost. Nine cases of DVT and two cases of PE were identified with an incidence of 0.84% and 0.19%, respectively, and a total VTE incidence of 1.03%. Only one patient developed heparin-induced thrombocytopenia (HIT). No cases of other heparin-associated complications were observed. VTE incidence rates reported in the literature are wide-ranging and poorly capture the effect of any one chemoprophylaxis regimen in the burn population. Our center uses a single, safe, and cost-effective protocol effecting a low VTE rate comparable to that of large national retrospective studies.

Anti-Factor Xa Levels in Low-weight Surgical Patients Receiving Enoxaparin for Venous Thromboembolism Prophylaxis: A Prospective Cohort Study

Enoxaparin is indicated for thromboprophylaxis in non-orthopedic surgical patients at a fixed dose of 40 mg daily. According to the US Food and Drug Administration’s enoxaparin prescribing information, this dose exposes low-weight patients (males < 57 kg, females < 45 kg) to a higher risk of bleeding. This study aimed to determine the rate of achieving a prophylactic peak anti-factor Xa (AFXa) level in low-weight surgical patients using enoxaparin 30 mg daily. Low-weight patients admitted for abdominopelvic or noncardiac thoracic surgery from May 2018 to May 2019 were prospectively studied. After receiving daily enoxaparin 30 mg, peak AFXa levels were assessed for achieving a prophylactic level (0.2-0.5 IU/mL). In 121 patients, the proportion of achieving a prophylactic peak AFXa level was 66.1%. More females (84.8%) achieved a prophylactic level compared to males (54.7%, P = .001). All out-of-range peak AFXa levels (33.9%) were sub-prophylactic. The median peak AFXa level was lower in males (0.24 [0.1-0.47] IU/mL) than females (0.31 [0.1-0.5] IU/mL; P < .001). On univariate analysis, female sex and weight were associated with achieving a prophylactic peak AFXa level. On multivariate analysis, only female sex was independently associated with an adequate prophylactic AFXa level (odds ratio 3.17, 95% CI: 1.32-11.94; P = .014). Four venous thromboembolism events (3.3%) were observed in patients with sub-prophylactic peak AFXa levels (9.7%). Two-thirds of low-weight surgical patients achieved a prophylactic peak AFXa level using daily enoxaparin 30 mg. This dose is likely to provide adequate thromboprophylaxis in low-weight females.

Clinical Characteristics Associated With Higher Enoxaparin Dosing Requirements for Venous Thromboembolism Prophylaxis in Trauma Patients

INTRODUCTION

Enoxaparin dosed by an anti-Xa trough level is effective at reducing venous thromboembolism (VTE) in trauma patients. We identified the patient characteristics associated with higher enoxaparin dosing based on anti-Xa trough levels.

METHODS

A retrospective review was conducted on trauma patients admitted between August 2014 and February 2018 who received enoxaparin dosed by the anti-Xa trough level. Patients who received enoxaparin < 50 mg every 12 hours were compared to those who required ≥ 50 mg every 12 hours.

RESULTS

Of the 246 patients included, 32 (13.0%) required enoxaparin ≥ 50 mg every 12 hours to achieve the prophylactic trough level. Factors associated with a higher dose of enoxaparin were male (96.8% vs. 3.2%, P < .01), younger age (39.5 vs. 52.7 years, P < .01), higher creatinine clearance (CrCl) (125.9 vs. 93.7 mL/min, P < .01), higher body surface area (2 m² vs. 1.8 m², P < .01), and higher injury severity score (18.4 vs. 10.8, P < .01). Height, weight, and body mass index were not significant factors. On regression analysis, CrCl was the only independent predictor for higher enoxaparin dose. There was an increased deep venous thrombosis rate in the higher dose cohort (12.5% vs. 0, P < .01) but no significant differences in transfusion rates.

CONCLUSION

Trauma patients who require higher enoxaparin doses to achieve prophylactic anti-Xa trough levels have a higher CrCl. Patients with high CrCl may benefit from an initial higher dose of enoxaparin to achieve a target anti-Xa level in a shorter time interval to decrease VTE risk.

Venous thromboembolism in burns patients: Are we underestimating the risk and underdosing our prophylaxis?

BACKGROUND

Burns patients exhibit all factors of Virchow's triad and are thus at high theoretical risk of venous thromboembolism (VTE). At our tertiary referral burns unit, a standard dose of low molecular weight heparin, which acts primarily by inhibiting Factor Xa, is given for thromboprophylaxis. However, the pharmacokinetics of enoxaparin are altered following a burn injury, and thus burns patients are likely underdosed on their thromboprophylaxis. The objectives of this study were to determine the incidence and risk factors for VTE among burns patients at the Victorian Adult Burns Service (VABS) and to determine the adequacy of the current enoxaparin thromboprophylaxis regimen through measurement of anti-factor Xa (AFXa) levels and comparison with established reference ranges.

METHODS

This study consisted of two parts. In part 1, the Burns Registry of Australia and New Zealand (BRANZ) was reviewed for cases of VTE in burns patients admitted to the VABS from 2013 - 2018. Part 2 was a prospective study that determined peak and trough AFXa levels in patients admitted to the VABS with >10% total body surface area (TBSA) burns.

RESULTS

Part 1. Totally, 1,475 patients were admitted to the VABS between 2013 - 2018. There were 20 cases of VTE (1.36%). Percent TBSA of burn (OR = 1.04, 95% CI: 1.03 - 1.06), full thickness burns (OR = 2.78, 95% CI: 1.15 - 6.73), ICU admission (OR = 15.08, 95% CI: 5.01 - 45.44), mechanical ventilation (OR = 10.62, 95% CI: 4.05 - 27.91), operative procedures (OR = 1.43, 95% CI: 1.29 - 1.59), and a longer hospital stay (OR = 1.05, 95% CI: 1.04 - 1.07) were all associated with an increased VTE risk. Part 2. A total of 20 participants with >10% TBSA burns were recruited to the prospective study. Peak anti Factor Xa (AFXa) levels were measured for all 20 participants with 15% recording an initial prophylactic peak AFXa level within reference range. Upon subsequent measurements, 50% of participants reached a prophylactic peak AFXa level. Trough AFXa levels were measured for 17 participants with no participant recording an initial or subsequent trough AFXa level at or above the prophylactic threshold.

CONCLUSION

Our study demonstrates a high incidence of VTE among burns patients at the VABS, especially among the major burns patients, and a thromboprophylaxis protocol that is ineffective in achieving prophylactic levels of AFXa level. The evidence suggests a need to evaluate different dosing protocols among burns patients in order to improve AFXa levels, with the aim of decreasing incidence of VTE in high-risk patients.

Dosage reduction of low weight heparin in patients with renal dysfunction: Effects on anti-Xa levels and clinical outcomes

Background

To prevent bio-accumulation of low molecular weight heparins (LMWHs) in patients with decreased kidney function, dosage reduction and anti-Xa monitoring has been suggested. The aim of this study was to investigate the effect of pre-emptive dosage reduction of LMWH on anti-Xa levels. Furthermore, we investigated the association between anti-Xa levels and bleeding, thrombotic events and mortality.

Methods

In this single center study, we followed 499 patients with decreased renal function in whom anti-Xa levels were measured. We observed how many patients had anti-Xa levels that fell within the reference range, with a standard protocol of a pre-emptive dosage reduction of LMWH (25% reduction in patients with an estimated glomerular filtration rate (eGFR) between 30 and 60 ml/min/1.73m² and a reduction of 50% in patients with an eGFR below the 30 ml/min/1.73m²). Furthermore, Cox proportional hazard analyses were used to estimate hazard ratios to investigate the association between anti-Xa levels and major bleeding, thrombotic events and mortality within three months of follow-up.

Results

In a cohort of 499 patients (445 dalteparin and 54 nadroparin users), a pre-emptive dosage reduction of LMWH led to adequate levels of anti-Xa in only 19% of the patients (12% for the dalteparin users and 50% for nadroparin users). We did not find an association between anti-Xa levels and bleeding, thrombosis or mortality.

Conclusion

Pre-emptive dosage reduction of LMWH leads to low anti-Xa levels in a large proportion, but this was not associated with bleeding, thrombosis or mortality.

Assessment of Anti-Factor Xa Levels of Patients Undergoing Colorectal Surgery Given Once-Daily Enoxaparin Prophylaxis: A Clinical Study Examining Enoxaparin Pharmacokinetics

Importance

Between 4% and 12% of patients undergoing colorectal surgery and receiving enoxaparin, 40 mg per day, have a postoperative venous thromboembolism (VTE) event. An improved understanding of why "breakthrough" VTE events occur despite guideline-compliant prophylaxis is an important patient safety question.

Objective

To determine the proportion of patients undergoing colorectal surgery who received adequate anticoagulation based on peak anti-factor Xa (aFXa) levels while receiving enoxaparin at 40 mg per day.

Design, Setting, and Participants

This prospective, nonrandomized clinical trial was conducted between February 2017 and July 2018 with 90-day follow-up at a quaternary academic medical center in the Intermountain West and included patients undergoing colorectal surgery who had surgery after receiving general anesthesia, were admitted for at least 3 days, and received enoxaparin, 40 mg once daily.

Interventions

All patients had aFXa levels measured after receiving enoxaparin 40 mg per day. Patients whose aFXa level was out of range entered the trial's interventional arm where real-time enoxaparin dose adjustment and repeated aFXa measurement were performed.

Main Outcomes and Measures

Primary outcome: in-range peak aFXa levels (goal range, 0.3-0.5 IU/mL) with enoxaparin, 40 mg per day. Secondary outcomes: (1) in-range trough aFXa levels (goal range, 0.1-0.2 IU/mL) and (2) the proportion of patients with in-range peak aFXa levels from enoxaparin, 40 mg once daily, vs the real-time enoxaparin dose adjustment protocol.

Results

Over 16 months, 116 patients undergoing colorectal surgery (65 women [56.0%]; 99 white individuals [85.3%], 13 Hispanic or Latino individuals [11.2%], and 4 Pacific Islander individuals [3.5%]; mean [range] age, 52.1 [18-85] years) were enrolled. Among 106 patients (91.4%) whose peak aFXa level was appropriately drawn, 72 (67.9%) received inadequate anticoagulation (aFXa < 0.3 IU/mL) with enoxaparin, 40 mg per day. Weight and peak aFXa levels were inversely correlated (r2 = 0.38). Forty-seven patients (77%) had a trough aFXa level that was not detectable (ie, most patients had no detectable level of anticoagulation for at least 12 hours per day). Real-time enoxaparin dose adjustment was effective. Patients were significantly more likely to achieve an in-range peak aFXa with real-time dose adjustment as opposed to fixed dosing alone (85.4% vs 29.2%, P < .001).

Conclusions and Relevance

This study supports the finding that most patients undergoing colorectal surgery receive inadequate prophylaxis from enoxaparin, 40 mg once daily. These findings may explain the high rate of "breakthrough" VTE observed in many clinical trials.

Trial Registration

ClinicalTrials.gov identifier: NCT02704052.

Rethinking the one-size-fits-most approach to venous thromboembolism prophylaxis after radical cystectomy

OBJECTIVES

Empirically dosed enoxaparin is routinely given in the postoperative period for venous thromboembolism (VTE) prophylaxis after radical cystectomy (RC). Patient-specific factors may alter its pharmacokinetics, and it is unclear whether this leads to levels sufficient for antithrombosis. We sought to evaluate variability of anti-factor Xa levels in a cohort of RC patients receiving perioperative enoxaparin prophylaxis.

MATERIAL AND METHODS

Patients undergoing RC at a single institution were placed on a postoperative pathway that included enoxaparin. An anti-factor Xa level was drawn 2 to 4 hours after the third dose. The target range for prophylaxis was 0.3 IU/ml to 0.5 IU/ml.

RESULTS

The primary outcome was anti-factor Xa level. Demographics, operative time, hospital course, and 30-days post-operative VTE were compared by anti-factor Xa level group using univariate and multivariable analyses. Between January 2018 and 2019, 107 RC patients remained on pathway and were included in our analysis. Sixty-five (61%) were below target range for VTE prophylaxis.  A single VTE event (0.9%) occurred in a subprophylactic individual. The subprophylactic group had a significantly higher body mass index (P < 0.01) than those within target range.

CONCLUSIONS

Higher body mass index was associated with subprophylactic enoxaparin dosing after RC. Nearly two-thirds of patients had below target anti-factor Xa levels. This suggests that dosing could be further individualized, but given the low incidence of VTE, implications of dose-adjusted prophylaxis on VTE prevention remain unknown.

Fixed or Weight-Tiered Enoxaparin After Thoracic Surgery for Venous Thromboembolism Prevention

BACKGROUND

Venous thromboembolism is an important patient safety issue in thoracic surgery patients. The optimal enoxaparin dose remains unclear. This multicenter pre/post clinical trial compared the pharmacokinetics of fixed versus weight-tiered enoxaparin, and their impact on 90-day venous thromboembolism and bleeding.

METHODS

Thoracic surgery patients were prospectively enrolled using a pre/post study design. Cohort 1 received enoxaparin 40 mg daily, and cohort 2 received a weight-tiered regimen: less than 70 kg received 30 mg daily; 70 kg to 89.9 kg received 40 mg once daily; and 90 kg or more received 50 mg daily. The primary study outcome was peak anti-factor Xa levels in response to fixed or weight-tiered enoxaparin. Secondary outcomes included trough anti-factor Xa, 90-day symptomatic venous thromboembolism, and 90-day clinically relevant bleeding.

RESULTS

One hundred thirty-one patients were prospectively enrolled, including 65 in the fixed-dose cohort and 66 in the weight-tiered cohort. No patient was lost to follow-up. Weight-tiered enoxaparin was not significantly more likely to produce adequate anticoagulation (peak anti-factor Xa 0.3 IU/mL or greater) when compared with fixed-dose enoxaparin (44.3% vs 48.2%, P = .67). Weight-tiered enoxaparin was not more likely to avoid over-anticoagulation (peak anti-factor Xa 0.5 IU/mL or greater) when compared with fixed-dose enoxaparin (3.3% vs 3.6%, P = 1.00). The groups had no significant difference in trough anti-factor Xa. Observed rates of 90-day symptomatic venous thromboembolism and clinically relevant bleeding were low (0% and 3.1%, respectively) and were not significantly different between groups.

CONCLUSIONS

This multicenter pre/post clinical trial did not show a pharmacokinetic advantage to weight-tiered enoxaparin, when compared with fixed-dose enoxaparin, in thoracic surgery patients. (Clinicaltrials.gov identifier: NCT03251963.).

Racial and Ethnic Differences in Response to Anticoagulation: A Review of the Literature

INTRODUCTION

Anticoagulants are among the most frequently prescribed medications in the United States. Racial and ethnic disparities in incidence and outcomes of thrombotic disorders are well-documented, but differences in response to anticoagulation are incompletely understood.

OBJECTIVE

The objective of this review is to describe the impact of race and ethnicity on surrogate and clinical end points related to anticoagulation and discuss racial or ethnic considerations for prescribing anticoagulants.

METHODS

A PubMed and MEDLINE search of clinical trials published between 1950 and May 2018 was conducted using search terms related to anticoagulation, specific anticoagulant drugs, race, and ethnicity. References of identified studies were also reviewed. English-language human studies on safety or efficacy of anticoagulants reporting data for different races or ethnicities were eligible for inclusion.

RESULTS

Seventeen relevant studies were identified. The majority of major trials reviewed for inclusion either did not include representative populations or did not report on the racial breakdown of participants. Racial differences in pharmacokinetics, dosing requirements, drug response, and/or safety end points were identified for unfractionated heparin, enoxaparin, argatroban, warfarin, rivaroxaban, and edoxaban.

CONCLUSIONS

Race appears to influence drug concentrations, dosing, or safety for some but not all direct oral anticoagulants. This information should be considered when selecting anticoagulant therapy for nonwhite individuals.

Prophylactic Enoxaparin Adjusted by Anti-Factor Xa Peak Levels Compared with Recommended Thromboprophylaxis and Rates of Clinically Evident Venous Thromboembolism in Surgical Oncology Patients

BACKGROUND

Studies among populations at high risk of venous thromboembolism (VTE) have demonstrated that recommended doses for enoxaparin thromboprophylaxis are associated with high incidence of subprophylactic anti-factor Xa (anti-Xa) levels. This study examines the efficacy and safety of dose-adjusted enoxaparin guided by anti-Xa levels.

STUDY DESIGN

Patients undergoing abdominal cancer operation had dose adjustments based on peak anti-Xa levels to attain a target of >0.20 IU/mL were prospectively enrolled and compared with a historic cohort of patients receiving recommended thromboprophylaxis. Incidence of in-hospital VTE and major bleeding after changes in enoxaparin dosing were monitored.

RESULTS

The study population comprised 197 patients-64 patients in the prospective intervention group and 133 patients in the control group. Baseline characteristic were similar between the intervention and control groups, with the exception of the Caprini score (8.09 vs 7.26; p = 0.013). In the intervention group, 50 of 64 patients (78.1%) initially had subprophylactic peak anti-Xa levels. The VTE rates were lower in the intervention group than the control group (0% vs 8.27%; p = 0.018). There were no differences in major bleeding events (3.12% vs 1.50%; p = 0.597), rates of postoperative packed RBC transfusion (17.2% vs 23.3%; p = 0.426), or mean Hgb on discharge (9.58 vs 9.37g/dL; p = 0.414). Therapeutic anti-Xa levels correlated positively with age (65.7 vs 58.2 years; p = 0.022) and correlated negatively with operating room time (203 vs 281 minutes; p = 0.032) and BMI (25.3 vs 29.2 kg/m²; p = 0.037).

CONCLUSIONS

Thromboprophylactic enoxaparin 40 mg daily is often associated with subprophylactic peak anti-Xa levels. Dose adjustment based on anti-Xa levels increased the daily enoxaparin dose, resulting in a lower rate of in-hospital VTE without increased risk of bleeding.

Evaluation of prophylactic dosages of Enoxaparin in non-surgical elderly patients with renal impairment

Background

Thromboprophylaxis dosing strategies using enoxaparin in elderly patients with renal disease are limited, while dose adjustments or monitoring of anti-Xa levels are recommended. We sought to evaluate the efficacy and safety of enoxaparin 20 mg versus 30 mg subcutaneously daily by comparing anti-Xa levels, thrombosis and bleeding.

Methods

We conducted a prospective, single-blinded, single-center randomized clinical trial including non-surgical patients, 70 years of age or older, with renal disease requiring thromboprophylaxis. Patients were randomized to receive either 20 mg or 30 mg of enoxaparin. The primary endpoint was peak anti-Xa levels on day 3. Secondary endpoints included trough anti-Xa levels on day 3, achievement of within range prophylactic target peak anti-Xa levels and the occurrence of hemorrhage, thrombosis, thrombocytopenia or hyperkalemia during hospitalization.

Results

Thirty-two patients were recruited and sixteen patients were randomized to each arm. Mean peak anti-Xa level was significantly higher in 30 mg arm (n = 13) compared to the 20 mg arm (n = 11) 0.26 ± 0.11, 95%CI (0.18–0.34), versus 0.14 ± 0.09, 95CI (0.08–0.19) UI/ml, respectively; p = 0.004. Mean trough anti-Xa level was higher in 30 mg arm (n = 10) compared to the 20 mg arm (n = 16), 0.06 ± 0.03, 95CI (0.04–0.08) versus 0.03 ± 0.03, 95CI (0.01–0.05) UI/ml, respectively; p = 0.044. Bleeding events reported in the 30 mg arm were one retroperitoneal bleed requiring multiple transfusions, and in the 20 mg arm one hematuria. No thrombotic events were reported.

Conclusion

Peak anti-Xa levels provided by enoxaparin 20 mg were lower than the desired range for thromboprophylaxis in comparison to enoxaparin 30 mg.

Trial registration

The trial was retrospectively registered on ClinicalTrials.gov identifier: NCT03158792. Registered: May 18, 2017.

Double-Blind Randomized Clinical Trial to Examine the Pharmacokinetic and Clinical Impacts of Fixed Dose versus Weight-based Enoxaparin Prophylaxis: A Methodologic Description of the FIxed or Variable Enoxaparin (FIVE) Trial

Venous thromboembolism is an important patient safety in plastic surgery, and multiple clinical trials in the past 10 years have provided increased understanding of the risks and benefits of venous thromboembolism prevention strategies. This paper provides an exhaustive discussion of the rationale behind and methodology for an in progress randomized double-blind clinical trial in plastic surgery inpatients, in which the 2 study arms are enoxaparin 40 mg twice daily and enoxaparin 0.5 mg/kg twice daily. The trial's primary aims are to: (1) demonstrate whether enoxaparin 0.5 mg/kg twice daily is superior to enoxaparin 40 mg twice daily for the pharmacokinetic endpoint of overanticoagulation (anti-Factor Xa > 0.4 IU/mL) and (2) demonstrate whether enoxaparin 0.5 mg/kg twice daily is not inferior to enoxaparin 40 mg twice daily for the pharmacokinetic endpoint of underanticoagulation (anti-Factor Xa < 0.2 IU/mL). The results of this trial will provide Level I evidence to help guide plastic surgeon's choice of postoperative prophylactic anticoagulation.

Twice-Daily Enoxaparin among Plastic Surgery Inpatients: An Examination of Pharmacodynamics, 90-Day Venous Thromboembolism, and 90-Day Bleeding

BACKGROUND

Low anti-factor Xa level, indicative of inadequate enoxaparin dosing, has a significant association with 90-day venous thromboembolism events. The authors examined the pharmacodynamics of enoxaparin 40 mg twice daily and its correlation with anti-factor Xa level, postoperative venous thromboembolism, and bleeding.

METHODS

Adult patients were admitted after plastic and reconstructive surgery and received enoxaparin 40 mg twice daily. Peak anti-factor Xa levels, which quantify enoxaparin's antithrombotic effect, were drawn, with a goal level of 0.2 to 0.4 IU/ml. Ninety-day symptomatic venous thromboembolism and clinically relevant bleeding were identified.

RESULTS

The authors enrolled 118 patients who received enoxaparin 40 mg twice daily. Of these patients, 9.6 percent had low peak anti-factor Xa levels (<0.2 IU/ml), 62.6 percent had in-range peak anti-factor Xa levels (0.2 to 0.4 IU/ml), and 27.8 percent had high anti-factor Xa levels (>0.4 IU/ml). With enoxaparin 40 mg twice daily, 90.4 percent of patients received at least adequate prophylaxis. Patient weight predicted the rapidity of enoxaparin metabolism. Zero acute 90-day venous thromboembolism occurred. Eight patients (6.8 percent) had clinically relevant 90-day bleeding: clinical consequences ranged from cessation of enoxaparin prophylaxis to transfusion to operative hematoma evacuation.

CONCLUSIONS

When enoxaparin 40 mg twice daily is provided, 90 percent of patients receive at least adequate venous thromboembolism prophylaxis (anti-factor Xa level >0.2 IU/ml). However, 27 percent of the overall population is overtreated (anti-factor Xa level >0.4 IU/ml). These pharmacodynamics data likely explain the low rate of 90-day acute venous thromboembolism (0 percent) and the high rate of clinically relevant bleeding (6.8 percent) observed. Future studies are needed to better optimize the risks and benefits of enoxaparin prophylaxis in plastic and reconstructive surgery patients.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Enoxaparin 40 mg per Day Is Inadequate for Venous Thromboembolism Prophylaxis After Thoracic Surgical Procedure

BACKGROUND

Many patients undergoing thoracic surgical procedures have venous thromboembolism (VTE) events despite the receipt of chemical prophylaxis. Enoxaparin's pharmacologic impact can be quantified by using anti-Factor Xa (aFXa) levels. We hypothesized that enoxaparin 40 mg once daily would be inadequate for most inpatients undergoing thoracic surgical procedures and that a real-time dose adjustment algorithm would be effective.

METHODS

This prospective clinical trial enrolled inpatients who were to undergo a thoracic surgical procedure and placed on enoxaparin 40 mg once daily for VTE prophylaxis after surgical procedures. aFXa levels were used to measure the anticoagulant effect of enoxaparin once steady state had been reached. Patients whose aFXa levels were out of range received real-time enoxaparin dose adjustment and had repeat aFXa levels drawn.

RESULTS

Ninety-three inpatients undergoing thoracic surgical procedures were prospectively enrolled. The majority of patients (67.4%) had low peak aFXa levels (<0.3 IU/mL), indicative of inadequate enoxaparin prophylaxis, and 30.3% of patients had in-range aFXa levels (0.3 to 0.5 IU/mL). Patient weight had a moderate correlation (r² 0.38) with peak aFXa level. Patient weight, female sex, and preoperative creatinine were independent predictors of peak aFXa in a linear regression model. Real-time, protocol-driven enoxaparin dose adjustment allowed a significantly increased proportion of patients to achieve in-range aFXa levels (30.3% vs 97.6%, p < 0.001).

CONCLUSIONS

Enoxaparin 40 mg once daily is inadequate for most inpatients undergoing thoracic surgical procedures, based on a pharmacodynamic study of aFXa levels. Future research should examine the impact of weight-based once daily enoxaparin dosing versus twice daily enoxaparin dosing on prophylaxis adequacy.

Profilaxia da trombose venosa profunda em cirurgia bariátrica: estudo comparativo com doses diferentes de heparina de baixo peso molecular

Contexto

A cirurgia bariátrica é considerada a melhor opção para o tratamento da obesidade, cujos pacientes são considerados de alto risco para fenômenos tromboembólicos.

Objetivos

Comparar o uso de doses diferentes de heparina de baixo peso molecular (HBPM) na profilaxia da trombose venosa profunda (TVP) em pacientes candidatos à cirurgia bariátrica em relação ao risco de TVP, alteração na dosagem do fator anti-Xa e sangramento pré ou pós-operatório.

Métodos

Estudo comparativo transversal em pacientes submetidos à cirurgia bariátrica distribuídos em dois grupos, que receberam doses de HBPM de 40 mg (grupo controle, GC) e 80 mg (grupo de estudo, GE). Foram avaliados por ultrassonografia vascular e dosagem de KPTT, TAP, plaquetas e fator anti-Xa.

Resultados

Foram avaliados 60 pacientes, sendo 34 no GC e 26 no GE. Foi observada diferença significativa somente no peso (p = 0,003) e índice de massa corporal (p = 0,018) no GE em relação ao GC. Não houve diferença na dosagem de KPTT, TAP, plaquetas e fator anti-Xa entre os grupos. Não foram detectados TVP ou sangramentos significativos em ambos os grupos.

Conclusões

Não houve diferença estatisticamente significativa na utilização de doses maiores de HBPM na profilaxia da TVP em pacientes candidatos à cirurgia bariátrica em relação ao risco de TVP, dosagem do fator anti-Xa e sangramento pré ou pós-operatório.

Weight-Based Dosing for Once-Daily Enoxaparin Cannot Provide Adequate Anticoagulation for Venous Thromboembolism Prophylaxis

BACKGROUND

Surgeons commonly provide enoxaparin prophylaxis to high-risk patients to decrease venous thromboembolism risk. The authors' prior work demonstrated that most patients receive inadequate venous thromboembolism prophylaxis, based on anti-factor Xa level, when enoxaparin 40 mg/day is provided and that peak anti-factor Xa level correlates with weight. This study models a weight-based strategy for daily enoxaparin prophylaxis and its impact on anti-factor Xa levels.

METHODS

The authors enrolled plastic surgery patients who received enoxaparin 40 mg/day and had anti-factor Xa levels drawn. The enoxaparin dose of 40 mg was converted to a milligram-per-kilogram dose for each patient. Stratified analysis examined the milligram-per-kilogram dose that produced low, in-range, and high anti-factor Xa levels to identify the appropriate milligram-per-kilogram dose to optimize venous thromboembolism prevention and bleeding events.

RESULTS

Among 94 patients, weight-based dosing ranged from 0.28 to 0.94 mg/kg once daily. For peak and trough anti-factor Xa levels, there was nearly complete overlap for milligram-per-kilogram dosing that produced low versus in-range anti-factor Xa levels. For peak anti-factor Xa, there was nearly complete overlap for milligram-per-kilogram dosing that produced in-range versus high anti-factor Xa levels. Mean milligram-per-kilogram dose was not significantly different between patients who did or did not have postoperative venous thromboembolism (0.41 mg/kg versus 0.52 mg/kg; p = 0.085) or clinically relevant bleeding (0.48 mg/kg versus 0.51 mg/kg; p = 0.73).

CONCLUSIONS

Alterations in enoxaparin dose magnitude based on patient weight cannot allow a high proportion of patients to achieve appropriate anti-factor Xa levels when once-daily enoxaparin prophylaxis is provided. Future research should examine the impact of increased enoxaparin dose frequency on anti-factor Xa levels, venous thromboembolism events, and bleeding.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Prophylactic enoxaparin doses may be inadequate in patients undergoing abdominal cancer surgery

BACKGROUND

The incidence of venous thromboembolism has increased in patients following cancer surgery despite the increased use of prophylactic anticoagulants, suggesting standard doses may be inadequate. We sought to determine the adequacy of enoxaparin prophylaxis in patients undergoing abdominal cancer surgery.

METHODS

Peak and trough anti-Xa levels were measured in patients receiving enoxaparin thromboprophylaxis (40 mg daily or 30 mg twice daily, at the surgeon's discretion) after undergoing open abdominal cancer surgery at a single institution.

RESULTS

Fifty-five patients received enoxaparin 40 mg daily (group 1), 18 received 30 mg twice daily (group 2; total n = 73). There were no significant differences in gender, age, body mass index, creatinine clearance, diagnosis, or procedure between the two groups. Thirty-nine patients (53.4%) had inadequate peak anti-Xa levels (<0.2 IU/mL) and 69 patients (94.5%) had inadequate trough levels (≤0.1 IU/mL). Group 2 had lower mean peak levels (0.14 ± 0.02 IU/mL) than group 1 (0.22 ± 0.01, P = 0.003), and higher mean trough levels (0.06 ± 0.017) than group 1 (0.02 ± 0.004, P = 0.033). Group 2 had lower incidence of adequate peak anti-Xa levels than group 1 when adjusting for gender, age, body mass index, and preoperative creatinine clearance (OR 0.23, P = 0.039).

CONCLUSIONS

The majority of patients had inadequate anti-Xa levels following abdominal cancer surgery, calling into question standard prophylactic enoxaparin dosing.

An Evaluation of a Factor Xa-Based Clotting Time Test for Enoxaparin: A Proof-of-Concept Study

A well-accepted test for monitoring anticoagulation by enoxaparin is not currently available. As inadequate dosing may result in thrombosis or bleeding, a clinical need exists for a suitable test. Previous in silico and in vitro studies have identified factor Xa as an appropriate activating agent, and the phospholipid Actin FS as a cofactor for a Xa clotting time (TenaCT) test. A proof-of-concept study was designed to (1) explore the reproducibility of the TenaCT test and (2) explore factors that could affect the performance of the test. In vitro clotting time tests were carried out using plasma from 20 healthy volunteers. The effect of enoxaparin was determined at concentrations of 0.25, 0.50, and 1.0 IU/mL. Clotting times for the volunteers were significantly prolonged with increasing enoxaparin concentrations. Clotting times were significantly shortened for frozen plasma samples. No significant differences in prolongation of clotting times were observed between male and female volunteers or between the 2 evaluated age groups. The clotting times were consistent between 2 separate occasions. The TenaCT test was able to distinguish between the subtherapeutic and therapeutic concentrations of enoxaparin. Plasma should not be frozen prior to performing the test, without defining a frozen plasma reference range. This study provided proof-of-concept for a Xa-based test that can detect enoxaparin dose effects, but additional studies are needed to further develop the test.

Anti-Factor Xa measurements in acute care surgery patients to examine enoxaparin dose

BACKGROUND

The purpose of this study was to determine if fixed dose enoxaparin prophylaxis provided effective anticoagulation for acute care surgery patients and to examine whether a real-time enoxaparin dose adjustment algorithm optimized anticoagulation.

METHODS

Acute care surgical patients placed on enoxaparin prophylaxis 30 mg twice daily were recruited prospectively. Peak steady state aFXa levels were drawn with a goal peak aFXa range of 0.2-0.4 IU/ml. A real time dose adjustment algorithm was implemented for patients with out-of-range levels.

RESULTS

Fifty five patients were included. 56.4% of patients had low aFXa levels (<0.2 IU/mL). Real-time enoxaparin dose adjustment significantly increased the proportion of patients who achieved in-range peak aFXa levels, compared to standard dosing (74.5% vs 41.8%, p < 0.001). Patients with initial inadequate peak aFXa levels had a higher rate of 90-day post-operative VTE, although not statistically significant (16.1% vs. 8.3%, p = 0.50).

CONCLUSION

The majority of acute care surgery patients receive inadequate VTE prophylaxis with fixed enoxaparin dosing.

Inadequate Enoxaparin Dosing Predicts 90-Day Venous Thromboembolism Risk among Plastic Surgery Inpatients: An Examination of Enoxaparin Pharmacodynamics

BACKGROUND

Evidence-based plastic surgery guidelines support the effectiveness of once-daily enoxaparin prophylaxis. Despite prophylaxis, one in 25 highest risk patients has a venous thromboembolism event. The authors examined the pharmacodynamics of standard enoxaparin doses in plastic surgery patients to examine whether patient-level factors predict enoxaparin metabolism, whether inadequate enoxaparin dose predicts downstream venous thromboembolism events, and whether a pharmacist-driven dose-adjustment protocol was effective.

METHODS

The authors recruited adult plastic surgery patients who received postoperative enoxaparin at 40 mg/day. Steady-state peak anti-factor Xa levels, a marker of enoxaparin effectiveness and safety, were determined. Patients with out-of-range anti-factor Xa levels had real-time dose adjustment based on a written protocol. Patients were followed for 90-day venous thromboembolism events.

RESULTS

Ninety-four patients were recruited, and 44 percent had in-range peak anti-factor Xa levels in response to standard enoxaparin dosing. Patient-level factors including extent of surgical injury and gross weight were independent predictors of enoxaparin metabolism. Patients with low anti-factor Xa levels were significantly more likely to have 90-day venous thromboembolism (10.2 percent versus 0 percent; p = 0.041). Real-time dose adjustment allowed a significantly increased proportion of patients to have in-range levels (67.1 percent versus 44.3 percent; p = 0.002).

CONCLUSIONS

Based on pharmacodynamic data, the majority of plastic surgery patients receive inadequate enoxaparin prophylaxis using fixed dosing. Patient-level factors can predict how patients will metabolize enoxaparin, and patients who receive inadequate enoxaparin prophylaxis are significantly more likely to have downstream venous thromboembolism events. Individualization of enoxaparin prophylaxis may minimize perioperative venous thromboembolism risk and further improve patient safety after plastic and reconstructive surgery procedures.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

Goal directed enoxaparin dosing provides superior chemoprophylaxis against deep vein thrombosis

INTRODUCTION

Optimal enoxaparin dosing for deep venous thrombosis (DVT) prophylaxis remains elusive. Prior research demonstrated that trauma patients at increased risk for DVT based upon Greenfield's risk assessment profile (RAP) have DVT rates of 10.8% despite prophylaxis. The aim of this study was to determine if goal directed prophylactic enoxaparin dosing to achieve anti-Xa levels of 0.3-0.5IU/ml would decrease DVT rates without increased complications.

MATERIALS AND METHODS

Retrospective review of trauma patients having received prophylactic enoxaparin and appropriately timed anti-Xa levels was performed. Dosage was adjusted to maintain an anti-Xa level of 0.3-0.5IU/ml. RAP was determined on each patient. A score of ≥5 was considered high risk for DVT. Sub-analysis was performed on patients who received duplex examinations subsequent to initiation of enoxaparin therapy to determine the incidence of DVT.

RESULTS

306 patients met inclusion criteria. Goal anti-Xa levels were met initially in only 46% of patients despite dosing of >40mg twice daily in 81% of patients; however, with titration, goal anti-Xa levels were achieved in an additional 109 patients (36%). An average enoxaparin dosage of 0.55mg/kg twice daily was required for adequacy. Bleeding complications were identified in five patients (1.6%) with three requiring intervention. There were no documented episodes of HIT. Subsequent duplex data was available in 197 patients with 90% having a RAP score >5. Overall, five DVTs (2.5%) were identified and all occurred in the high-risk group. All patients were asymptomatic at the time of diagnosis.

CONCLUSION

An increased anti-Xa range of 0.3-0.5IU/ml was attainable but frequently required titration of enoxaparin dosage. This produced a lower rate of DVT than previously published without increased complications.

Adjusted value of thromboprophylaxis in hospitalized obese patients: A comparative study of two regimens of enoxaparin: The ITOHENOX study

Thromboprophylaxis is a mainstay of hospital care in patients at high risk of thrombosis. Fixed doses of low-molecular-weight heparin (LMWH) are recommended for thromboprophylaxis in patients admitted to hospital for an acute medical condition. However, the distribution of LMWH is weight-based, and the efficacy of standard doses in obese patients may be decreased. Data for obese patients are mainly available in bariatric surgery with extremely obese patients who are at greater risk of venous thromboembolism than those hospitalized for a medical condition. We conducted a randomized control trial in medically obese inpatients (BMI≥30kg/m²) assessing two regimens of enoxaparin (40mg and 60mg SQ daily) in order to determine whether a stronger dosage would achieve higher anti-Xa level suitable for thromboprophylaxis. Between September 2013 and April 2015, 91 patients were included in the study (mean (±standard deviation) age was 70.4±10.7years, average BMI 37.8±6.4kg/m²). Main indications of thromboprophylaxis were mainly acute infection (50%), acute respiratory failure (10%), acute congestive heart failure (9%) and acute rheumatic disorders (18%). Average anti-Xa activity, measured 4h after the third administration of enoxaparin was 0.25±0.09IU/mL in group 1 (enoxaparin 40mg) and 0.35±0.13IU/mL in group 2 (enoxaparin 60mg) (P<10^-3). The proportions of patients with normal anti-Xa activity (between 0.32 and 0.54IU/mL) were 31% (n=11) and 69% (n=24) in group 1 and 2 respectively (P=0.007). The proportions of anti-Xa activity measurement below the normal range were 64% and 36% in group 1 and 2 (P<10^-3) respectively. Subgroup analysis focusing on high weight patients (above 100kg, n=45) showed a marked difference in the proportion of patients with normal anti-Xa activity between group 1 (9%) and 2 (44%) (P=0.009). No venous thromboembolism occurred during the study and one patient in group 1 died because of hemorrhagic shock due to a gastric ulcer. Incidence of adverse events was not different between the two groups (P=0.52). In conclusion, the ITOHENOX study shows in medically obese inpatients that thromboprophylaxis with enoxaparin 60mg provides higher control of anti-Xa activity, without more bleeding complications than the standard enoxaparin regimen. This trial is registered with ClinicalTrials.gov, number NCT01707732.