How do I safely switch a patient from warfarin (Coumadin) to apixaban (Eliquis), considering indication, renal and hepatic function, age, weight, INR threshold, dosing adjustments, and need for bridging?

Switching from Warfarin to Apixaban

Stop warfarin and start apixaban when the INR drops below 2.0—this is the single most important threshold to prevent both overlapping anticoagulation (which increases bleeding risk) and gaps in coverage. 1

Step-by-Step Transition Protocol

1. Monitor INR and Initiate Switch

• Discontinue warfarin and check INR daily until it falls below 2.0 1
• Start apixaban immediately when INR <2.0—do not wait for INR to normalize to 1.0 1
• No bridging anticoagulation with heparin or low-molecular-weight heparin is required during this transition 1

2. Determine the Correct Apixaban Dose

The dose depends on whether the patient meets the "2-of-3" dose-reduction criteria:

Use apixaban 5 mg twice daily unless the patient meets at least 2 of these 3 criteria: 2, 1

1. Age ≥80 years
2. Body weight ≤60 kg
3. Serum creatinine ≥1.5 mg/dL

Use apixaban 2.5 mg twice daily only when ≥2 criteria are present 2, 1

3. Calculate Renal Function Properly

• Use the Cockcroft-Gault equation with actual body weight—not eGFR—because this is what the FDA label and clinical trials used 2
• For CrCl 15-29 mL/min: automatically use 2.5 mg twice daily regardless of age or weight 2
• For CrCl >30 mL/min: apply the standard 2-of-3 criteria above 2
• Apixaban has only 27% renal clearance, making it safer than dabigatran (80%) or rivaroxaban (66%) in renal impairment 2, 3

4. Screen for Drug Interactions

• Reduce apixaban to 2.5 mg twice daily if the patient is taking combined P-glycoprotein AND strong CYP3A4 inhibitors (ketoconazole, ritonavir, itraconazole) 2, 1
• Avoid apixaban entirely with strong CYP3A4 inducers (rifampin, carbamazepine, phenytoin) 2, 1

Common Pitfalls to Avoid

• Do not reduce the dose based on a single criterion—this is the most common prescribing error, with 9.4-40.4% of apixaban prescriptions involving inappropriate underdosing 2
• Do not use eGFR for dosing decisions—always calculate CrCl with Cockcroft-Gault 2
• Do not bridge with parenteral anticoagulation—the short half-life of warfarin and rapid onset of apixaban (3 hours to therapeutic effect) make bridging unnecessary and increase bleeding risk 2, 1
• Do not start apixaban while INR is ≥2.0—warfarin's effect on INR can persist for days, creating dangerous overlap 1

Special Considerations by Indication

For Atrial Fibrillation

• Standard dosing applies: 5 mg twice daily (or 2.5 mg twice daily if ≥2 criteria met) 2, 1
• No loading dose required—therapeutic anticoagulation is achieved within 3 hours 2

For Venous Thromboembolism (Recent DVT/PE)

• Use 10 mg twice daily for the first 7 days, then 5 mg twice daily thereafter 1
• The 2-of-3 dose-reduction criteria do not apply to acute VTE treatment 2

For Dialysis or CrCl <15 mL/min

• FDA recommends 5 mg twice daily; reduce to 2.5 mg twice daily if age ≥80 years OR weight ≤60 kg (only one criterion required in dialysis) 2
• European guidelines contraindicate apixaban in dialysis—this represents a regulatory discrepancy 2

Monitoring After the Switch

• No routine INR monitoring is needed once on apixaban 2
• Reassess renal function at least annually, or every 3-6 months if CrCl <60 mL/min 2
• Monitor for bleeding symptoms, particularly gastrointestinal bleeding in elderly patients 2

Why Apixaban Over Warfarin

• 49% reduction in hemorrhagic stroke compared to warfarin (0.24% vs 0.47% per year) 2
• 31% reduction in major bleeding versus warfarin 2
• No dietary restrictions or need for frequent INR monitoring 4
• Lower risk of anticoagulant-related nephropathy compared to warfarin, which occurs twice as frequently in CKD patients 2