Can a patient be on a heparin (unfractionated heparin) drip and warfarin (coumarin) together?

Can You Be on a Heparin Drip and Warfarin Together?

Yes, heparin drip and warfarin are routinely used together during the initial treatment of acute thrombotic conditions, and this combination is standard practice recommended by multiple guidelines. 1, 2

When and Why This Combination Is Used

Heparin and warfarin must be overlapped for 4-5 days when initiating anticoagulation for acute venous thromboembolism, atrial fibrillation with high stroke risk, or other thrombotic conditions requiring immediate anticoagulation. 1, 2, 3

The rationale for concurrent use is straightforward:

• Warfarin has a delayed onset of action, taking 4-5 days to achieve therapeutic anticoagulation, so heparin provides immediate protection during this vulnerable period 2, 4
• Heparin works immediately by activating antithrombin, while warfarin requires depletion of existing vitamin K-dependent clotting factors (II, VII, IX, X) 5, 3
• The FDA-approved warfarin label explicitly states: "conversion to warfarin may begin concomitantly with heparin therapy" and recommends overlapping "for 4 to 5 days, until warfarin has produced the desired therapeutic response" 2

Specific Protocol for Concurrent Use

Start both medications simultaneously on day 1, continue full-dose heparin throughout, and only discontinue heparin after warfarin achieves therapeutic INR (2.0-3.0) for at least 24 hours, preferably 2 consecutive days. 1, 2

The step-by-step approach:

• Initiate heparin with 5,000 unit IV bolus followed by continuous infusion of 30,000-40,000 units per 24 hours, targeting aPTT 1.5-2.5 times control 3
• Start warfarin on the same day (day 1) at 10 mg daily for outpatients or 5 mg for elderly patients 1
• Continue full therapeutic doses of both medications—do not reduce heparin dose when warfarin is started 2, 3
• Monitor INR daily initially, and continue heparin until INR is therapeutic (2.0-3.0) for minimum 24 hours 1, 2
• This overlap typically requires 4-5 days but may extend to 7-10 days depending on individual response 3

Critical Monitoring Considerations

Warfarin significantly elevates aPTT independent of heparin, which can lead to inappropriate heparin dose reductions and subtherapeutic anticoagulation. 6

Key monitoring pitfalls to avoid:

• For each 1.0 increase in INR from warfarin, the aPTT increases by approximately 16 seconds (95% CI: 10-22 seconds) even without changing heparin dose 6
• In one study, of 29 blood samples with supratherapeutic aPTT during combined therapy, 13 had therapeutic heparin levels and 10 had subtherapeutic heparin levels 6
• Do not reflexively decrease heparin dose when aPTT rises during warfarin initiation—verify with heparin anti-Xa levels if available 6
• When drawing blood for PT/INR in patients on both medications, timing matters: draw at least 5 hours after IV heparin bolus, 4 hours after stopping continuous infusion, or 24 hours after subcutaneous heparin 2

When This Combination Should NOT Be Used

Heparin bridging is increasingly recognized as harmful in most periprocedural settings and for patients on direct oral anticoagulants (DOACs). 5, 7

Situations where bridging causes more harm than benefit:

• For elective procedures in patients on chronic warfarin with low-to-moderate thrombotic risk, bridging increases major bleeding 2-3 fold (2.7% vs 0.5%, p=0.01) without reducing thromboembolism 5, 7
• A Japanese study of 16,977 patients showed significantly increased postprocedure GI bleeding AND thromboembolism in bridged patients 5
• For colonoscopy with polypectomy, LMWH bridging increases postpolypectomy hemorrhage without decreasing thromboembolic events 5
• Bridging should only be considered for very high-risk patients: mechanical mitral valve, recent VTE (<3 months), severe thrombophilia, or CHADS-VASc >5 5

Special Clinical Scenarios

Acute Myocardial Infarction in Patients Already on Warfarin

For AMI patients already on warfarin requiring PCI, administer reduced-dose heparin bolus (60-70 U/kg instead of standard dose) under ACT guidance. 8

• Check baseline INR before heparin administration to avoid excessive anticoagulation 8
• Target lower ACT range (250-350 seconds, or 200-250 seconds with GPIIb/IIIa inhibitors) 8
• Monitor more frequently (every 4-6 hours) and target lower aPTT range (1.5 times control rather than 1.5-2.5 times) if INR already therapeutic 8

Pregnancy with Mechanical Heart Valves

Pregnant patients with mechanical valves requiring high-dose warfarin (>5 mg/day) should switch to LMWH or UFH during first trimester, then may resume warfarin in second trimester. 5

• Warfarin doses >5 mg/day carry 0.6-10% risk of embryopathy, but only 0.45-0.9% with doses <5 mg/day 5
• LMWH should be dosed at 100 anti-Xa U/kg twice daily with levels maintained at 0.5-1.0 U/mL 4-6 hours post-injection 5
• At 36 weeks gestation, switch to IV heparin for delivery planning due to risk of fetal intracranial bleeding 5

Unstable Angina/Non-STEMI

For acute coronary syndromes, the combination of heparin plus aspirin is superior to either agent alone, with the triple combination (heparin + aspirin + warfarin) showing borderline additional benefit. 5

• Heparin plus aspirin reduced cardiovascular death and MI by 33% (95% CI: 22-56%) compared to aspirin alone in meta-analysis of 1,353 patients 5
• Continuous IV heparin (10,000 U bolus every 6 hours × 24 hours, then 7,500 U every 6 hours × 5 days) combined with aspirin reduced composite endpoint to 1.4% vs 6.0% with placebo 5