What anticoagulation should be initiated and at what dose in a patient with confirmed Proximal Deep Vein Thrombosis (DVT) after a post-operative day of left hip replacement?

Anticoagulation for Confirmed Proximal DVT After Hip Replacement

For a patient with confirmed proximal DVT after hip replacement surgery, initiate therapeutic anticoagulation with a direct oral anticoagulant (DOAC) as first-line therapy, specifically rivaroxaban 15 mg twice daily with food for 21 days, followed by 20 mg once daily, or apixaban 10 mg twice daily for 7 days followed by 5 mg twice daily. 1

First-Line Treatment: DOACs

The 2020 American Society of Hematology guidelines establish DOACs as superior to vitamin K antagonists (VKAs) for acute DVT treatment, with a conditional recommendation based on moderate certainty evidence 1. DOACs demonstrate significantly reduced major bleeding risk (6 fewer events per 1000 patients; 95% CI, 9 fewer to 3 fewer) compared to warfarin, with equivalent efficacy for preventing recurrent thrombosis. 1

Specific DOAC Dosing Regimens

Rivaroxaban (FDA-approved for VTE treatment):

• 15 mg orally twice daily with food for 21 days
• Then 20 mg once daily with food for continued treatment 2
• Critical advantage: No initial parenteral anticoagulation required 1

Apixaban (studied in AMPLIFY trial):

• 10 mg orally twice daily for 7 days
• Then 5 mg twice daily for continued treatment 1
• Demonstrated noninferior efficacy with significantly lower bleeding rates than enoxaparin/warfarin 1

Dabigatran:

• Requires initial parenteral anticoagulation for median 9 days before initiation 1
• 150 mg orally twice daily after parenteral lead-in 1
• Not preferred in this acute setting due to mandatory parenteral lead-in requirement 1

Alternative: Low Molecular Weight Heparin

If DOACs are contraindicated (severe renal impairment with CrCl <30 mL/min, moderate-to-severe liver disease, or antiphospholipid syndrome), use therapeutic-dose enoxaparin: 1

• 1 mg/kg subcutaneously every 12 hours 3
• Continue for minimum 5 days AND until INR ≥2.0 for 2 consecutive days if transitioning to warfarin 1
• For patients >150 kg, consider dose adjustment to 40 mg every 12 hours 3

Duration of Anticoagulation

Minimum 3 months of therapeutic anticoagulation is mandatory for proximal DVT. 1 The American Society of Hematology recommends:

• For provoked DVT (post-surgical): 3 months minimum 1
• For unprovoked DVT: Extended therapy beyond 3 months if low-to-moderate bleeding risk 1
• Reassess at 3 months based on bleeding risk versus thrombosis recurrence risk 1

Critical Contraindications and Adjustments

Renal Function Requirements

• Rivaroxaban: Avoid if CrCl <15 mL/min; use with caution if CrCl 15-29 mL/min 2
• Apixaban: Avoid if CrCl <25 mL/min 1
• Enoxaparin: Reduce to 1 mg/kg once daily if CrCl <30 mL/min 3

Special Populations Requiring VKA Instead of DOAC

• Antiphospholipid syndrome (DOACs show inferior efficacy) 1
• Severe renal impairment (CrCl <30 mL/min) 1
• Moderate-to-severe liver disease 1

Common Pitfalls to Avoid

Do not continue prophylactic-dose anticoagulation when therapeutic DVT is diagnosed. The post-operative prophylaxis regimen (enoxaparin 40 mg once daily or rivaroxaban 10 mg once daily) used after hip replacement is inadequate for treating established proximal DVT 3, 2, 4. Immediate escalation to therapeutic dosing is required 1.

Do not delay anticoagulation while awaiting additional testing. Once proximal DVT is objectively confirmed by imaging, therapeutic anticoagulation should begin immediately unless absolute contraindications exist 1.

Avoid warfarin monotherapy without parenteral overlap. If warfarin is chosen, it must be overlapped with parenteral anticoagulation (LMWH or UFH) for minimum 5 days AND until INR ≥2.0 for 2 consecutive days 1.

Monitor for heparin-induced thrombocytopenia (HIT) if using LMWH. Orthopedic surgery patients have up to 5% risk of HIT 5. If platelet count drops >50% or thrombosis worsens despite anticoagulation 5-14 days after heparin initiation, stop all heparin products immediately and initiate argatroban 5.

Timing Considerations Post-Operatively

For patients already receiving prophylactic anticoagulation post-hip replacement who develop DVT:

• If on prophylactic enoxaparin (30-40 mg daily): Increase immediately to therapeutic dosing (1 mg/kg every 12 hours) 3, 4
• If on prophylactic rivaroxaban (10 mg daily): Switch to therapeutic dosing (15 mg twice daily with food) 2
• Do not wait for "washout" period when escalating from prophylactic to therapeutic dosing of the same agent 1