Non-therapeutic anti-FXa levels are common among medical ward patients treated with enoxaparin

How enoxaparin underdosing and sex contribute to achieving therapeutic anti-Xa levels

Introduction

Anti-Xa serves as a clinical surrogate for assessing the efficacy and bleeding risk in patients treated with enoxaparin for thromboembolic events. Evidence from the literature and empirical observations suggest that patients are underdosed in clinical practice to avoid bleeding complications. This study aimed to investigate such underdosing of enoxaparin and its potential impact on achieving therapeutic anti-Xa levels.

Methods

This multicentric, retrospective, observational study included patients with acute ischemic stroke due to atrial fibrillation. All patients received enoxaparin in the therapeutic setting with subsequent anti-Xa measurements. The one-sample, one-tailed Wilcoxon signed-rank test was used to identify a significant difference between the doses administered and the recommended daily dose. Logistic regression model analysis was performed to identify additional predictors affecting achievement of the therapeutic anti-Xa target range. Stepwise forward-backward selection with Akaike's information criterion as metric was applied to refine the logistic regression model.

Results

A total of 145 patients from the university hospitals of St. Pölten and Tulln in Lower Austria were included. The median daily enoxaparin dose administered was 1.23 mg/kg, resulting in an overall target range achievement rate of 66%. As compared to recommended therapeutic doses, significant underdosing of enoxaparin was evident in both participating centers (p < 0.001). The calculated threshold dose to achieve the therapeutic target range with a 90% probability was 1.5 mg/kg enoxaparin daily. Female sex was found to be a strong independent predictor of achieving a therapeutic target range (OR 9.44; 95% CI 3.40-30.05, p < 0.001).

Conclusion

Despite the underdosing observed in both centers, therapeutic anti-Xa levels were achieved with lower than recommended doses of enoxaparin, and women required even lower doses than men. These findings warrant further confirmation by prospective studies.

Monitoring anti-Xa levels in patients with cancer-associated venous thromboembolism treated with bemiparin

OBJECTIVE

To analyze the relationship between therapeutic (weight-adjusted) dose of bemiparin and anti-Xa activity in patients with venous thromboembolism (VTE) and cancer in comparison with a cohort of patients with VTE without cancer, and its relationship with outcomes.

MATERIALS AND METHODS

This is a prospective cohort study that comprised a cohort of patients with cancer-associated VTE and a cohort of non-cancer patients with VTE, all of them treated with bemiparin. The ethics committee approved the study and informed consent was obtained from the patients.

RESULTS

One hundred patients were included (52 with cancer and 48 without cancer), with a median follow-up of 9.8 months. Mean anti-Xa activity was 0.89 (± 0.33) UI/mL in oncological patients and 0.83 (± 0.30) UI/mL in non-cancer patients (mean difference - 0.05 95% CI - 0.18; 0.06). A multiple linear regression model showed that anti-Xa peak was associated with the dose/kg independently of possible confounding variables (presence of cancer, age, sex and eGFR-estimated Glomerular Filtration Rate), in a way that for every 1 UI of dose/kg increase, the anti-Xa peak activity increased 0.006 UI/mL (95% CI 0.003; 0.009) (p < 0.001). The predictive capacity of anti-Xa peak in the oncology cohort showed an area under the ROC curve of 0.46 (95% CI 0.24-0.68), 0.70 (95% CI 0.49-0.91) and 0.74 (95% CI 0.44-0.94) for death, first bleeding and recurrence of VTE, respectively, and none was statistically significant.

CONCLUSION

In patients with venous thromboembolism treated with bemiparin, anti-Xa levels were not influenced by the presence of cancer.

Achievement of therapeutic anti-Xa levels in a proven heparin-resistant patient through the use of nontraditional high-dose enoxaparin

OBJECTIVE

To describe the successful use of high-dose enoxaparin therapy (1.5 mg/kg subcutaneously twice daily) to attain a therapeutic anti-factor Xa (anti-Xa) level in a cancer patient with heparin resistance.

CASE SUMMARY

A proven heparin-resistant patient with venous thromboembolism (VTE) and lung cancer who required approximately 66 000 units of unfractionated heparin daily was successfully transitioned to an off-label high-dose enoxaparin (OLHDE) 1.5 mg/kg subcutaneously twice daily. The patient was maintained on this same dose, and therapeutic levels were confirmed via use of the anti-Xa monitoring test. The patient was able to be discharged from the medical floor on this same dose with no further complications of VTE noted. No adverse events from this dosing were observed during the duration of therapy.

DISCUSSION

Options for overcoming heparin resistance are limited to case reports and small studies. The best course of treatment in the cancer patient is unclear. OLHDE allowed for the transition from intravenous to subcutaneous medication and transition off the medical floor. This case supports the use of OLHDE as a therapeutic option in heparin-resistant patients with cancer. Further study is needed to confirm the efficacy of OLHDE in this patient population.

CONCLUSION

High-dose enoxaparin may be an option to treat cancer patients with confirmed heparin resistance and venous thromboembolism.

Non-therapeutic anti-Xa levels in medical patients receiving anticoagulant therapy with enoxaparin

INTRODUCTION

Anticoagulant activity of enoxaparin is not routinely monitored even when previous studies have shown a high pharmacological variability. The aim of this study is to determine the prevalence of non-therapeutic anti-Xa levels among medical patients using enoxaparin as anticoagulant therapy and to point out potential risk factors related to the risk of having a sub-therapeutic level.

MATERIALS AND METHODS

Anti-Xa levels were measured in a cohort of sixty patients with medical indication for enoxaparin. Patients were categorized according to anti-Xa levels as follows: suboptimal anticoagulation (<0.5 IU/ml), optimal anticoagulation (between 0.5 and 1.2 IU/ml) or overanticoagulated (>1.2 IU/ml). Demographic and clinical variables and the use of concomitant medications were described for each group. Univariate and multivariate analysis were performed to assess the relationship between sub-optimal anticoagulation and potential predictive variables. A linear regression analysis was done to assess the relationship between anti-Xa activity, age, weight, body mass index, administered dose/weight and creatinine clearance.

RESULTS

The mean anti-Xa activity was 0.71±0.32 UI/ml. Thirty one percent of patients had anti-Xa levels out of the therapeutic range, most of them (twenty-eight percent of total population) with a sub-therapeutic level. None of the variables were associated with the risk of a sub-therapeutic anti-Xa level.

CONCLUSION

Almost one third of patients receiving enoxaparin had anti-Xa levels out of the therapeutic range. We need more studies to determine the clinical relevance of these findings.