Anti-factor Xa levels in obese patients receiving enoxaparin for treatment and prophylaxis indications

Venous Thromboembolism Prophylaxis in Obstetric Patients

Venous thromboembolism (VTE), including both pulmonary embolism (PE) and deep vein thrombosis (DVT), is the leading cause of maternal death in developed countries. Pregnancy is associated with an increased risk of VTE due to physiologic changes during the obstetric period that promote a hypercoagulable state. Appropriate use of prophylactic anticoagulants can decrease the event rate of thrombus formation in at-risk patients. In the United States, there is not a validated risk-assessment tool for VTE in obstetric patients or a clear consensus on initiation and optimal dosing strategy for the prophylactic use of anticoagulants. This article reviews the mechanism of coagulation disturbance that leads to an increased risk of VTE in obstetric patients, as well as the available literature surrounding pharmacologic prophylaxis.

Weight-adjusted dosing of tinzaparin for thromboprophylaxis in obese medical patients

Background

The optimal dose of tinzaparin for prophylaxis in obese medical patients is not well defined.

Objectives

To evaluate the anti-Xa activity in obese medical patients on tinzaparin prophylaxis adjusted for actual bodyweight.

Methods

Patients with a body mass index of ≥30 kg/m² treated with 50 IU/kg tinzaparin once daily were prospectively included. Anti-Xa and anti-IIa activity; von Willebrand factor antigen and von Willebrand activity; factor VIII activity; D-dimer, prothrombin fragments; and thrombin generation were measured 4 hours after subcutaneous injection between days 1 and 14 after the initiation of tinzaparin prophylaxis.

Results

We included 121 plasma samples from 66 patients (48.5% women), with a median weight of 125 kg (range, 82-300 kg) and a median body mass index of 41.9 kg/m² (range, 30.1-88.6 kg/m²). The target anti-Xa activity of 0.2 to 0.4 IU/mL was achieved in 80 plasma samples (66.1%); 39 samples (32.2%) were below and 2 samples (1.7%) above the target range. The median anti-Xa activity was 0.25 IU/mL (IQR, 0.19-0.31 IU/mL), 0.23 IU/mL (IQR, 0.17-0.28 IU/mL), and 0.21 IU/mL (IQR, 0.17-0.25 IU/mL) on days 1 to 3, days 4 to 6, and days 7 to 14, respectively. The anti-Xa activity did not differ among the weight groups (P = .19). Injection into the upper arm compared to the abdomen resulted in a lower endogenous thrombin potential, a lower peak thrombin, and a trend to a higher anti-Xa activity.

Conclusion

Dosing of tinzaparin adjusted for actual bodyweight in obese patients achieved anti-Xa activity in the target range for most patients, without accumulation or overdosing. In addition, there is a significant difference in thrombin generation depending on the injection site.

Strategies involving low-molecular-weight heparin for the treatment and prevention of venous thromboembolism in patients with obesity: A systematic review and meta-analysis

INTRODUCTION

Recent studies have indicated that the dosage of LMWH in patients with specific weights may be controversial. Therefore, we conducted a meta-analysis to explore an appropriate dosage of LMWH for the prevention and treatment of venous thromboembolism (VTE) in patients with obesity.

MATERIALS AND METHODS

We searched the PubMed, EMBASE, and Cochrane Library databases up to July 23, 2022. Study selection, bias analysis, and information extraction were performed by three independent reviewers. The occurrence or recurrence of VTE and bleeding events were the primary outcomes we assessed.

RESULTS

Eleven studies (a total of 6266 patients) were included in the prevention group, and 6 studies (a total of 3225 patients) were included in the treatment group. For VTE prophylaxis, compared with the standard-dosage group, the high-dosage group had a lower incidence of VTE (OR: 0.47, 95% CI: 0.27-0.82, P=0.007) and a similar incidence of bleeding events (OR: 0.86, 95% CI: 0.69-1.08, P=0.020). For VTE therapy, compared to the standard-dosage group, the reduced-dosage group had a similar incidence of VTE recurrence (OR: 0.86, 95% CI: 0.11-6.84, P=0.89) but a lower incidence of bleeding events (OR: 0.30, 95% CI: 0.10-0.89, P=0.03).

CONCLUSION

In patients with obesity, increasing the dosage of LMWH is a more appropriate option for the prevention of VTE. Due to the limited evidence, reducing the therapeutic dosage of LMWH requires careful consideration. Larger-scale, well-designed randomized controlled trials are necessary.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/display_record.php?, identifier ID=CRD42022298128.

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.

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.

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.

Comparative Effectiveness and Safety of Direct Oral Anticoagulants in Obese Patients with Atrial Fibrillation

BACKGROUND

Unlike warfarin direct oral anticoagulants (DOACs) are administered in fixed doses, which raises concerns of its effectiveness on larger patients. Data from randomized trials are limited on the safety and efficacy of DOACs in morbidly obese individuals with atrial fibrillation (AF).

METHODS

We analyzed a cohort of obese (≥ 120 kg) and morbidly obese (BMI > 40 kg/m²) patients from the Veterans Health Administration system with AF who initiated apixaban, rivaroxaban, dabigatran, or warfarin between years 2012 and 2018. We used inverse probability of treatment weighting (IPTW) and Cox proportional hazards regression models to evaluate the relative hazard of death, myocardial infarction (MI), ischemic stroke, heart failure (HF), and bleeding events between oral anticoagulant (OAC) groups while censoring for medication cessation.

RESULTS

We identified 6052 obese patients on apixaban, 4233 on dabigatran, 4309 on rivaroxaban, and 13,417 on warfarin (mean age 66.7 years, 91% males, 80.4% whites). At baseline patients on apixaban had the lowest glomerular filtration rate and highest rates of previous stroke and MI compared to other OACs. Among patients with weight ≥ 120 kg and those with BMI > 40 kg/m², all DOACs were associated with lower risk of any hemorrhage, hemorrhagic stroke, and gastrointestinal (GI) bleeding. Patients with BMI > 40 kg/m² treated with DOACs had similar ischemic stroke risk with those on warfarin.

CONCLUSIONS

In this large cohort of obese Veterans Health Administration system patients, the use of DOACs resulted in lower hemorrhagic complications than warfarin while maintaining efficacy on ischemic stroke prevention.

Prophylactic Use of Enoxaparin in Adolescents During Bariatric Surgery-a Prospective Clinical Study

INTRODUCTION

Severe obesity predisposes youth to a higher risk of venous thromboembolism (VTE). This study evaluates a BMI-stratified prophylactic dosing regimen of enoxaparin in adolescents with severe obesity undergoing surgery.

METHODS

Adolescents aged 12-20 years received prophylactic enoxaparin at 40 mg SC (for a BMI < 50 kg/m²) and 60 mg SC (for a BMI ≥ 50 kg/m²) every 12 h until discharge. Blood samples were drawn at pre-dose, 1, 2, 4, 6, and 12 h. Plasma Anti-Factor Xa (Anti-FXa) activity was used as a surrogate marker for enoxaparin pharmacokinetics.

RESULTS

Ten female and two male obese adolescents (age range 14-19 years) had a mean BMI of 49.9 kg/m² (38.4-58 kg/m²). Four patients had a BMI of less than 50 kg/m² and received 40 mg enoxaparin, resulting in a mean dosage of 0.352 ± 0.070 mg/kg body weight. Eight patients were dosed with 60 mg enoxaparin every 12 h, resulting in a mean dosage of 0.395 ± 0.028 mg/kg. Peak plasma anti-FXa activity (C_max) ranged from 0.14 to 0.30 IU/mL, median C_max was 0.205 IU/mL. Median T_max was 5.67 h (range 3.78-7.52 h). Median AUC_i was 1.00 h IU/mL (range 0.42-1.67 h IU/mL). Ten out of 12 patients (83%) reached the primary endpoint with anti-FXa activity in the range for VTE prevention (0.1-0.3 IU/mL).

CONCLUSIONS

Our dosing scheme of 40 mg vs. 60 mg enoxaparin stratified according to BMI proved to be effective in reaching prophylactic anti-FXa activity in 83% of adolescent patients.