What is the recommended protocol for bridging heparin (unfractionated heparin (UFH) or low molecular weight heparin (LMWH)) with warfarin?

Recommended Protocol for Bridging Heparin with Warfarin

The recommended protocol for bridging heparin with warfarin requires overlapping both medications for 4-5 days until the INR reaches therapeutic range, with heparin discontinued once the INR is therapeutic for at least 24 hours. 1

General Bridging Principles

• Bridging anticoagulation is defined as the administration of a short-acting anticoagulant (LMWH or UFH) during interruption of warfarin therapy when the INR is below therapeutic range 2
• Heparin should be continued until the INR returns to therapeutic levels to ensure continuous anticoagulation 2
• The decision to use bridging therapy should balance the risks of thromboembolism and bleeding 2

Specific Bridging Protocol

Starting Warfarin While on Heparin

• Begin warfarin therapy concomitantly with heparin (UFH or LMWH) 1
• Continue full-dose heparin therapy overlapped with warfarin for 4-5 days, until warfarin has produced the desired therapeutic response as determined by INR 1
• Once warfarin has produced the desired INR, heparin may be discontinued 1

Dosing Considerations for Heparin

• For therapeutic-dose LMWH: enoxaparin 1 mg/kg twice daily or 1.5 mg/kg once daily; dalteparin 200 IU/kg once daily 2
• For therapeutic-dose UFH: IV infusion adjusted to maintain aPTT 1.5-2.5 times control or anti-factor Xa level of 0.3-0.7 IU/mL 2
• Once-daily LMWH dosing is preferred over twice-daily dosing (grade 2C) for most patients 3

Laboratory Monitoring During Bridging

• For patients on warfarin, check INR at least weekly during initiation of therapy and at least monthly when anticoagulation is stable 2
• When measuring PT/INR in patients receiving both heparin and warfarin, blood should be drawn at least:
  • 5 hours after the last IV bolus dose of heparin
  • 4 hours after cessation of continuous IV infusion of heparin
  • 24 hours after the last subcutaneous heparin injection 1

Special Patient Populations

Patients with Mechanical Heart Valves

• Bridging therapy with UFH or LMWH is recommended for patients with mechanical heart valves undergoing procedures requiring warfarin interruption 2
• For patients with mechanical prosthetic heart valves, some centers hospitalize patients and administer IV UFH until 4 hours prior to surgery 2
• Warfarin is recommended for patients with mechanical heart valves, with target INR based on type and location of prosthesis (2.0-3.0 or 2.5-3.5) 2

Patients with Renal Impairment

• For patients with severe renal insufficiency (CrCl <30 mL/min), caution is advised with LMWH due to potential accumulation 2, 3
• Consider UFH as an alternative to LMWH in patients with severe renal impairment 4

Common Pitfalls to Avoid

• Inadequate overlap period: Failing to overlap heparin and warfarin for at least 4-5 days can lead to inadequate anticoagulation 1
• Premature discontinuation of heparin: Discontinuing heparin before warfarin reaches therapeutic levels can create a window of inadequate anticoagulation 2, 1
• Residual anticoagulant effect: A residual anticoagulant effect from therapeutic-dose LMWH may be detected in approximately 1 in 6 patients prior to procedures, particularly in elderly patients 5
• Improper timing of INR measurement: Measuring INR too soon after heparin administration can lead to inaccurate results 1

Bridging Protocol for Perioperative Management

• For patients requiring interruption of warfarin for procedures:
  • Stop warfarin 5 days before surgery 2
  • Start LMWH or UFH 1 day after acenocoumarol interruption, or 2 days after warfarin interruption 2
  • Administer the last dose of LMWH at least 12 hours before the procedure 2
  • Resume LMWH or UFH 1-2 days after surgery, depending on hemostatic status, but at least 12 hours after the procedure 2
  • Resume warfarin on day 1 or 2 after surgery at the pre-operative maintenance dose plus a 50% boost dose for two consecutive days 2
  • Continue LMWH or UFH until the INR returns to therapeutic levels 2

By following this protocol, clinicians can ensure effective anticoagulation while minimizing risks of thromboembolism during the transition between heparin and warfarin therapy.