What is the dosage for atrial fibrillation (a fib) anticoagulation?

Anticoagulation Dosing for Atrial Fibrillation

For patients with atrial fibrillation, oral anticoagulation should be dosed based on stroke risk assessment using the CHA₂DS₂-VASc score, with direct oral anticoagulants (DOACs) preferred over vitamin K antagonists for non-valvular atrial fibrillation. 1

Risk Stratification and Anticoagulation Decision Algorithm

1. Assess stroke risk using CHA₂DS₂-VASc score:

   • Low risk (score = 0): No anticoagulation recommended
   • Intermediate risk (score = 1): Consider oral anticoagulation
   • High risk (score ≥ 2): Oral anticoagulation recommended 1

2. Choose appropriate anticoagulant:

   • First choice: Direct oral anticoagulants (DOACs)
   • Second choice: Warfarin (if DOACs contraindicated)
   • Alternative: Aspirin (only if oral anticoagulation contraindicated)

DOAC Dosing Recommendations

Apixaban (Preferred DOAC)

• Standard dose: 5 mg twice daily
• Reduced dose (2.5 mg twice daily) if patient has at least 2 of:
  • Age ≥ 80 years
  • Body weight ≤ 60 kg
  • Serum creatinine ≥ 1.5 mg/dL 2, 3
• For severe renal impairment (CrCl 15-29 mL/min): 2.5 mg twice daily
• For hemodialysis patients: Apixaban is the only DOAC specifically mentioned in guidelines for use in this population 2

Dabigatran

• Standard dose: 150 mg twice daily for CrCl > 30 mL/min
• Reduced dose: 75 mg twice daily for CrCl 15-30 mL/min 4
• Contraindicated: In mechanical heart valves 4

Rivaroxaban

• Standard dose: 20 mg once daily with food
• Reduced dose: 15 mg once daily for CrCl 15-50 mL/min
• Contraindicated: In CrCl < 15 mL/min 2

Edoxaban

• Standard dose: 60 mg once daily
• Reduced dose: 30 mg once daily for CrCl 15-50 mL/min 1

Warfarin Dosing

• Target INR: 2.0-3.0 for non-valvular AF 1
• Higher target INR (2.5-3.5): For patients with rheumatic heart disease, mechanical valves, or prior thromboembolism 1
• Monitoring: INR weekly during initiation, then monthly when stable 1

Important Clinical Considerations

1. Renal function assessment:

   • Calculate creatinine clearance before starting any DOAC
   • Regularly monitor renal function, especially in elderly patients
   • Adjust dosing according to renal function changes 2

2. Drug interactions:

   • Check for P-glycoprotein and CYP3A4 inhibitors/inducers
   • Reduce DOAC dose or avoid when used with strong inhibitors 3, 4

3. Temporary interruption for procedures:

   • For apixaban: Discontinue 48 hours before elective surgery with significant bleeding risk
   • Resume at least 6 hours post-procedure if hemostasis achieved 2

4. Special populations:

   • Elderly (≥75 years): Higher bleeding risk; consider dose reduction
   • End-stage renal disease: Apixaban preferred over other DOACs 2
   • Mechanical heart valves: DOACs contraindicated; use warfarin 2, 4

Common Pitfalls to Avoid

1. Underdosing DOACs: Using reduced doses without meeting criteria increases stroke risk
2. Failure to adjust for drug interactions: Can lead to bleeding or thrombosis
3. Inappropriate aspirin use: Not adequate for stroke prevention in high-risk patients
4. Discontinuing anticoagulation after cardioversion: Continue based on CHA₂DS₂-VASc score, not rhythm status
5. Overlooking renal function: Critical for proper DOAC dosing

The evidence strongly supports DOACs over warfarin for non-valvular AF due to reduced risk of intracranial hemorrhage and mortality, with apixaban showing a 21% reduction in stroke/systemic embolism, 31% reduction in major bleeding, and 11% reduction in all-cause mortality compared to warfarin 2.