Should warfarin (Coumadin) be administered concurrently with heparin (unfractionated heparin) while the patient is on a DVT/PE (Deep Vein Thrombosis/Pulmonary Embolism) protocol, given a subtherapeutic International Normalized Ratio (INR) of 1.56?

From the Guidelines

I recommend giving the scheduled warfarin dose at 2300 while continuing the heparin drip at 12.5/hr, as this overlapping therapy is standard practice when transitioning from heparin to warfarin, according to the American Society of Clinical Oncology clinical practice guideline update 1. The heparin should continue until the INR reaches therapeutic range (typically 2.0-3.0), as the physician ordered to "stop heparin once INR is therapeutic."

The current INR of 1.56 is not yet therapeutic, so both medications should be administered concurrently. This overlap is necessary because warfarin takes several days to reach full anticoagulant effect, while heparin provides immediate anticoagulation, as outlined in the guideline update 1. Stopping heparin prematurely before warfarin becomes effective could leave the patient without adequate anticoagulation for their DVT/PE protocol, potentially increasing thrombosis risk.

Key points to consider:

• The patient's current INR of 1.56 is below the therapeutic range of 2.0-3.0, necessitating continued heparin administration 1.
• The guideline update recommends overlapping parenteral anticoagulants with warfarin for 5 to 7 days minimum and continuing until INR is in the therapeutic range for 2 consecutive days 1.
• Monitoring INR daily until it reaches therapeutic range is crucial to ensure the patient receives adequate anticoagulation and to minimize the risk of thrombosis or bleeding complications.
• The patient's complex medical history, including cancer, cardiac stents, and previous thromboembolic events, underscores the importance of careful anticoagulation management to prevent further complications.

From the FDA Drug Label

CONVERSION FROM HEPARIN THERAPY Since the anticoagulant effect of warfarin sodium tablets is delayed, heparin is preferred initially for rapid anticoagulation Conversion to warfarin sodium tablets may begin concomitantly with heparin therapy or may be delayed 3 to 6 days. To ensure continuous anticoagulation, it is advisable to continue full dose heparin therapy and that warfarin sodium tablets therapy be overlapped with heparin for 4 to 5 days, until warfarin sodium tablets have produced the desired therapeutic response as determined by PT/INR When warfarin sodium tablets have produced the desired PT/INR or prothrombin activity, heparin may be discontinued.

The patient can receive warfarin at 2300 while heparin drip is running at 12.5/HR, as the conversion from heparin therapy to warfarin sodium tablets can begin concomitantly with heparin therapy, and it is advisable to overlap heparin and warfarin therapy for 4 to 5 days until warfarin has produced the desired therapeutic response as determined by PT/INR 2. Heparin should not be stopped until warfarin sodium tablets have produced the desired PT/INR or prothrombin activity.

From the Research

Patient's Current Situation

The patient is currently on heparin for DVT/PE protocol and has a history of various medical conditions, including hypertension, diabetes, hypothyroidism, thyroid cancer, Hodgkin lymphoma, and cardiac stents. The doctor has restarted warfarin, with the first dose scheduled for 2300, and has noted to stop heparin once the INR is therapeutic. The last INR was 1.56.

Anticoagulation Therapy

• The patient is receiving heparin and warfarin, which are commonly used anticoagulants for treating and preventing thromboembolic events 3.
• The study by 3 suggests that heparin therapy should be initiated with a bolus dose of 70-100 units/kg, followed by an infusion of 15-25 units/kg/hr, and that warfarin should be started on day 1 or 2 of heparin therapy.
• Another study by 4 found that increasing proportions of time on heparin with an APTT ≥ 0.2 anti-X(a) U/mL and on warfarin with an INR ≥ 2.0 were associated with significant reductions in VTE recurrence.

INR and Anticoagulation

• The patient's current INR is 1.56, which is below the therapeutic range of 2.0-3.0 5.
• A study by 6 found that patients with stable INRs who experience a significant subtherapeutic INR value have a low risk of thromboembolism in the ensuing 90 days.
• Another study by 7 found that an INR ≥ 2.0 during ablation of atrial fibrillation provides a consistent anticoagulant milieu during the procedure, with lower heparin requirements.

Administration of Warfarin and Heparin

• The doctor's notes indicate that heparin should be stopped once the INR is therapeutic, but it is unclear whether the warfarin dose should be given while the heparin drip is still running 3.
• The study by 7 suggests that an INR ≥ 2.0 can reduce thromboembolic complications and may allow for lower heparin doses during procedures.
• However, the current INR is 1.56, which is below the therapeutic range, and the heparin drip is still running at 12.5 units/hr.