Should I start warfarin as an inpatient or switch to therapeutic enoxaparin (Lovenox) for anticoagulation?

Warfarin Initiation as Inpatient with Enoxaparin Bridging

Start warfarin immediately as an inpatient with concurrent therapeutic enoxaparin bridging—do not delay warfarin initiation or discharge the patient on enoxaparin alone if long-term oral anticoagulation is the goal. 1

Immediate Initiation Protocol

Begin both medications simultaneously on day 1:

• Warfarin dosing: Start 5 mg orally once daily for elderly, frail, hospitalized, or nutritionally compromised patients 1
• Enoxaparin bridging: Administer 1 mg/kg subcutaneously every 12 hours at therapeutic dose 1, 2
• No gap required: Initiate enoxaparin immediately—there is no need to wait after stopping any prior unfractionated heparin infusion 2

The seamless transition is safe because both agents work through similar anti-factor Xa mechanisms, and delaying creates unnecessary thrombotic risk 2.

Overlap Duration and INR Monitoring

Continue both medications overlapped for minimum 5 days until therapeutic INR achieved:

• Overlap enoxaparin and warfarin for at least 5 days 1
• Continue overlap until INR reaches 2.0-3.0 on two consecutive measurements 1
• Check INR daily during the overlap phase until therapeutic range achieved 1
• After reaching therapeutic INR twice consecutively, discontinue enoxaparin and discharge on warfarin monotherapy 1

This approach ensures adequate anticoagulation during warfarin's delayed onset of action (typically 4-6 days to therapeutic effect) 1.

Renal Function Adjustments

Assess creatinine clearance before initiating enoxaparin:

• CrCl ≥30 mL/min: Use standard enoxaparin 1 mg/kg every 12 hours 1
• CrCl <30 mL/min: Switch to unfractionated heparin infusion with aPTT monitoring (80 units/kg IV bolus, then 18 units/kg/hour adjusted to aPTT 2-2.5× control) 1
• Warfarin: No routine dose adjustment needed for renal impairment, but monitor more closely for bleeding risk 1

The critical distinction is that enoxaparin accumulates in severe renal dysfunction while warfarin does not require dose reduction 3, 1.

Special Population Considerations

Cancer patients require different management:

• Low-molecular-weight heparin monotherapy (enoxaparin alone) is preferred over warfarin for cancer-associated VTE 3, 4
• If warfarin transition is absolutely necessary in cancer patients, continue enoxaparin for at least 6 months rather than switching early 4
• The superior efficacy of LMWH over warfarin in cancer patients makes the standard bridging approach suboptimal in this population 3

Acute coronary syndrome patients:

• For NSTEMI managed conservatively, enoxaparin is reasonable for duration of hospitalization up to 8 days 3
• For STEMI with fibrinolysis, enoxaparin is reasonable instead of UFH 3
• Patients initially treated with enoxaparin should not be switched to UFH due to increased bleeding risk 3

Common Pitfalls to Avoid

Critical errors that increase morbidity:

• Do not discharge on enoxaparin alone if the plan is long-term warfarin—this delays definitive therapy and increases cost 1
• Do not wait 4-6 hours after stopping heparin to start enoxaparin—this creates an anticoagulation gap 2
• Do not use prophylactic enoxaparin doses (40 mg daily) when therapeutic bridging is indicated—the correct dose is 1 mg/kg every 12 hours 1, 4
• Do not stop enoxaparin before 5 days of overlap even if INR is therapeutic—premature discontinuation risks thrombosis 1
• Do not use standard enoxaparin dosing in severe renal impairment (CrCl <30)—this quadruples major bleeding risk 2

Inpatient vs Outpatient Decision

The inpatient setting is appropriate for warfarin initiation when:

• Patient requires close monitoring due to high bleeding risk, multiple comorbidities, or polypharmacy 1
• Severe renal impairment necessitates UFH instead of enoxaparin 1
• Acute coronary syndrome or acute VTE requires immediate therapeutic anticoagulation 3

Outpatient bridging with enoxaparin is reasonable when:

• Patient is stable, ambulatory, and capable of self-injection 5, 6
• No severe renal impairment or active bleeding 1
• Adequate outpatient INR monitoring is available 1

However, the question specifically asks about inpatient management, and starting both medications as an inpatient with daily INR monitoring until therapeutic is the standard approach 1. This typically requires 5-7 days of hospitalization for overlap and stabilization 3, 1.