Can You Add Enoxaparin to a Heparin Infusion?
No, you should not add enoxaparin to an ongoing heparin infusion—these anticoagulants should not be used concurrently due to significantly increased bleeding risk without proven additional benefit. 1
Why Concurrent Use Is Not Recommended
The 2015 American Heart Association guidelines explicitly state that EMS systems that do not currently administer heparin to suspected STEMI patients should not add this treatment, and emphasize careful consideration when combining anticoagulation strategies 1. While this guidance addresses prehospital heparin initiation, the underlying principle applies to combining different anticoagulants.
Evidence Against Combination Therapy
- Enoxaparin is recommended as an alternative to unfractionated heparin (UFH), not as an addition to it in acute coronary syndrome management 1
- The 2015 AHA guidelines state: "In systems in which UFH is currently administered in the prehospital setting for patients with suspected STEMI who are being transferred for PPCI, it is reasonable to consider prehospital administration of enoxaparin as an alternative to UFH" (Class IIa, LOE B-R) 1
- Multiple studies comparing enoxaparin versus UFH showed improved outcomes with enoxaparin alone, but no studies support combining them 1
Appropriate Anticoagulation Strategy
When to Choose Enoxaparin Over Heparin
For non-ST-elevation ACS with planned conservative approach: Either fondaparinux or enoxaparin are reasonable alternatives to UFH 1
For non-ST-elevation ACS with planned invasive approach: Either enoxaparin or UFH are reasonable choices, but select one 1
For STEMI patients being transferred for primary PCI: If UFH is already being administered, enoxaparin can be considered as a replacement, not an addition 1
Switching Between Anticoagulants
If you need to transition from heparin to enoxaparin:
- Discontinue the heparin infusion completely before initiating enoxaparin 2
- Standard enoxaparin dosing for ACS is 1 mg/kg subcutaneously every 12 hours (or 1 mg/kg once daily if age ≥75 years with dose reduction) 1
- No bridging or overlap period is necessary when switching from UFH to enoxaparin 1
Common Pitfalls to Avoid
- Never combine UFH and enoxaparin simultaneously—this dramatically increases bleeding risk without evidence of improved thrombotic outcomes 1
- Do not add enoxaparin "on top of" heparin for perceived inadequate anticoagulation—instead, ensure heparin dosing is adequate by checking aPTT (target 1.5-2.0 times control) 3, 2
- Avoid switching back and forth between anticoagulants—select one agent and continue it unless there is a specific contraindication or adverse event 1
- Remember that enoxaparin requires dose adjustment in renal insufficiency (CrCl <30 mL/min), whereas UFH does not 2
When Anticoagulation Appears Inadequate on Heparin
If a patient on heparin infusion appears to have inadequate anticoagulation:
- Check aPTT and adjust heparin dose to achieve target of 1.5-2.0 times control (50-70 seconds) 3, 2
- Standard heparin dosing is 60 U/kg bolus (max 4,000 U) followed by 12 U/kg/hour infusion (max 1,000 U/hour) 3
- Monitor aPTT at 3,6,12, and 24 hours after initiation, then 4-6 hours after any dose adjustment 3
- Consider whether the patient has heparin resistance (requiring higher doses) rather than adding a second anticoagulant 2