Residual Anti-Xa Activity After Last Treatment Dose of Enoxaparin

  • End date
    Jun 24, 2024
  • participants needed
  • sponsor
    Wake Forest University Health Sciences
Updated on 24 December 2021
elective surgery


The main objective of this study is to determine the time interval following the last treatment dose of enoxaparin at which the amount of anti-Xa level activity is reliably less than 0.2IU/mL in patients presenting for elective surgery.


Enoxaparin is a factor Xa inhibitor commonly used for both prophylaxis against and treatment of thromboembolism. It is also frequently used off-label as a perioperative bridge for patients that are chronically anticoagulated prior to surgery, such as those taking Warfarin. It is an attractive option for perioperative use secondary to its predictable pharmacologic profile and the lack of recommended routine blood monitoring. Therefore, it is common to encounter a patient who has recently received a treatment dose of Enoxaparin prior to presenting for surgery. For these patients, and those on other anticoagulant medications, published guidelines have been developed to help guide clinical decision-making when the anesthetic/analgesic plan includes regional anesthesia.1 Currently, these guidelines recommend that a minimum of 24-hours should elapse following the last treatment dose of Enoxaparin before a neuraxial procedure is performed. However, a recently completed quality improvement project conducted at Wake Forest Baptist Medical Center found that almost 60% of patients presenting for surgery while on treatment dose enoxaparin still had significant anticoagulant activity 24-hours following their last dose, as demonstrated by anti-Xa level assay testing. Given that the risk of epidural hematoma formation is increased in the setting of abnormal coagulation parameters2, the significance of this finding is that the risk of bleeding complications following a neuraxial procedure may still be increased 24-hours after the last treatment dose of enoxaparin.

While the routine use of anti-Xa level testing may be a viable option to determine when residual enoxaparin activity is present before proceeding with a neuraxial procedure on a patient-by-patient basis, it is not universally available at all hospitals. Therefore, it is important to determine the time interval following the last enoxaparin dose at which the likelihood that a clinically relevant amount of residual anti-Xa level activity no longer persists, so that providers can confidently proceed with a neuraxial procedure when anti-Xa level testing is not available.

Condition Anticoagulants and Bleeding Disorders, Surgery, Regional Anesthesia Morbidity
Treatment Enoxaparin
Clinical Study IdentifierNCT03296033
SponsorWake Forest University Health Sciences
Last Modified on24 December 2021


Yes No Not Sure

Inclusion Criteria

Eligible patients need
to be on treatment dose (1mg/kg twice daily or 1.5mg/kg daily) enoxaparin at the time of presentation for elective surgery
and must be able to accurately report the timing of their last dose and the administered dosage
Patients must also be between the ages of 18-100 years of age
and must be able to give written consent to participate

Exclusion Criteria

Patients with severe renal insufficiency (creatinine clearance <30ml/min) will be excluded from the study, as the elimination of enoxaparin is known to be affected in this patient population
Pregnant patients will also be excluded, as the elimination and metabolism of enoxaparin is known to be altered in this patient population, and dose adjustments are recommended if treatment dose enoxaparin is used during pregnancy
Patients who are receiving enoxaparin as a bridge from another anti-Xa inhibiting medication will be excluded as this could unpredictably affect the results of anti-Xa testing. These medications include: Apixaban, Edoxaban, Fondaparinux, and Xarelto
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