How to switch from injectable anticoagulants to oral anticoagulants, such as novel oral anticoagulants (NOACs) like apixaban (Eliquis) or rivaroxaban (Xarelto), or warfarin, in patients with conditions like atrial fibrillation or venous thromboembolism?

Switching from Injectable to Oral Anticoagulants

When transitioning from injectable anticoagulants (such as LMWH or unfractionated heparin) to oral anticoagulants, discontinue the injectable agent and start the oral anticoagulant at the time the next scheduled dose of the injectable would have been given—no bridging or overlap is required. 1, 2

Switching to NOACs (Direct Oral Anticoagulants)

For patients transitioning from parenteral anticoagulants to NOACs (apixaban, rivaroxaban, dabigatran, or edoxaban):

• Stop the injectable anticoagulant (LMWH, fondaparinux, or unfractionated heparin) 1, 2
• Start the NOAC 0-2 hours before the next scheduled dose of the injectable agent would have been administered 2
• For continuous unfractionated heparin infusions, stop the infusion and start the NOAC at the same time 2
• No overlap or bridging therapy is needed due to the rapid onset of action of NOACs (therapeutic effect within 1-4 hours) 3, 1, 2

Specific NOAC Dosing

Apixaban dosing depends on the indication 1:

• For atrial fibrillation: 5 mg twice daily (or 2.5 mg twice daily if patient has ≥2 of: age ≥80 years, weight ≤60 kg, serum creatinine ≥1.5 mg/dL) 1
• For VTE treatment: 10 mg twice daily for 7 days, then 5 mg twice daily 1

Rivaroxaban dosing depends on the indication 2:

• For atrial fibrillation: 20 mg once daily (15 mg once daily if CrCl 15-50 mL/min) 2
• For VTE treatment: 15 mg twice daily for 21 days, then 20 mg once daily 2

Switching to Warfarin

The transition from injectable anticoagulants to warfarin requires a different approach due to warfarin's delayed onset of action:

• Start warfarin while continuing the injectable anticoagulant 3
• Continue both agents for a minimum of 5 days until the INR reaches therapeutic range (typically 2.0-3.0) 3
• Check INR daily during the overlap period 3
• Discontinue the injectable anticoagulant only when INR is ≥2.0 for two consecutive measurements 3
• This overlap is essential because warfarin takes 5-10 days to achieve therapeutic anticoagulation with large individual variation 3

Important Warfarin Considerations

• Monitor INR at least weekly during initiation, then monthly when stable 3
• Time in therapeutic range (TTR) should be kept as high as possible (ideally >70%) 3
• If TTR cannot be maintained, consider switching to a NOAC 3

Special Populations and Contraindications

Renal function assessment is critical before selecting an oral anticoagulant:

• NOACs are contraindicated in severe renal impairment (CrCl <30 mL/min for most agents, <15 mL/min for apixaban) 3
• Warfarin is preferred for patients on hemodialysis or with end-stage CKD (CrCl <15 mL/min) 3
• Assess renal function using Cockcroft-Gault calculation before initiating NOACs, as this was used in clinical trials 3
• Recheck renal function annually, or 2-3 times yearly if moderate impairment exists 3

NOACs are contraindicated in specific valve conditions:

• Mechanical heart valves require warfarin (INR 2.0-3.0 or 2.5-3.5 depending on valve type/location) 3
• Moderate-to-severe mitral stenosis requires warfarin, not NOACs 3

Clinical Advantages of NOACs Over Warfarin

When initiating oral anticoagulation in eligible patients, NOACs are preferred over warfarin:

• NOACs are recommended as first-line therapy for non-valvular atrial fibrillation and VTE 3
• Lower risk of intracranial hemorrhage compared to warfarin 3
• No routine laboratory monitoring required 4
• Rapid onset and offset of action eliminates need for bridging therapy 3, 4
• More predictable pharmacokinetics with fewer drug-food interactions 3

Common Pitfalls to Avoid

Do not bridge with injectable anticoagulants when switching to NOACs—this increases bleeding risk unnecessarily and provides no additional protection given NOACs' rapid onset 3, 1, 2, 4

Do not start warfarin without overlapping with injectable anticoagulants—this creates a period of inadequate anticoagulation during the first 5-10 days 3

Do not use NOACs in patients with mechanical valves—dabigatran showed increased thromboembolic and bleeding events in this population 3

Do not forget to assess and document renal function—this determines appropriate NOAC dosing and whether NOACs can be used at all 3