Apixaban Dosing for a 74-Year-Old Woman with Atrial Fibrillation
The standard dose is 5 mg orally twice daily for this 74-year-old patient, unless she meets at least 2 of the following 3 criteria: age ≥80 years, body weight ≤60 kg, or serum creatinine ≥1.5 mg/dL—in which case the dose should be reduced to 2.5 mg twice daily. 1, 2, 3, 4
Dosing Algorithm
Since this patient is 74 years old, she does not meet the age criterion (≥80 years) for dose reduction. 1, 3, 4 You must now assess the other two criteria:
- Body weight: If she weighs ≤60 kg (132 lbs), this counts as one dose-reduction criterion 1, 3, 5
- Serum creatinine: If her serum creatinine is ≥1.5 mg/dL, this counts as one dose-reduction criterion 1, 3, 5
If she meets both the weight AND creatinine criteria (2 out of 3 total), prescribe 2.5 mg twice daily. 1, 2, 3, 4
If she meets only one or neither of these criteria, prescribe the standard dose of 5 mg twice daily. 1, 2, 3, 4
Critical Pitfall to Avoid
The most common prescribing error with apixaban is inappropriate dose reduction based on a single criterion rather than requiring two—studies show that 60.8% of patients receiving reduced-dose apixaban do not actually meet the criteria for dose reduction. 6 Do not reduce the dose based solely on:
- Age alone (she's only 74, not ≥80) 1, 3
- Perceived bleeding risk without meeting formal criteria 5
- Renal function alone unless it meets BOTH the creatinine ≥1.5 mg/dL threshold AND another criterion 5
- Creatinine clearance cutoffs (apixaban dosing is NOT based on CrCl thresholds like other DOACs) 5
Renal Function Considerations
- Calculate creatinine clearance using the Cockcroft-Gault equation to fully assess renal function 5
- Apixaban has only 27% renal clearance, making it relatively safer in renal impairment compared to other direct oral anticoagulants 5
- Even with moderate renal impairment (CrCl 30-50 mL/min), the standard 5 mg twice daily dose is appropriate unless the formal dose-reduction criteria are met 1, 2
- Apixaban is contraindicated only if CrCl <15 mL/min and the patient is NOT on dialysis 1, 2
Drug Interactions Requiring Dose Adjustment
If this patient is taking potent dual P-glycoprotein and CYP3A4 inhibitors (ketoconazole, itraconazole, clarithromycin, ritonavir), reduce the dose from 5 mg to 2.5 mg twice daily regardless of other criteria. 3 Conversely, avoid concomitant use of potent P-glycoprotein and CYP3A4 inducers (carbamazepine, phenytoin, rifampin, St. John's wort). 1, 3
Monitoring After Initiation
- No routine coagulation monitoring (INR) is required 2, 5
- Assess renal function at least annually, and more frequently if CrCl is 30-50 mL/min or if clinical deterioration occurs 2, 5
- Monitor for signs of bleeding or thromboembolism 2
Evidence Supporting This Approach
The ARISTOTLE trial demonstrated that apixaban 5 mg twice daily reduced stroke or systemic embolism by 21% compared to warfarin (HR 0.79,95% CI 0.66-0.95) and reduced major bleeding by 31%. 2, 3 For patients meeting dose-reduction criteria, the 2.5 mg twice daily dose maintained efficacy while reducing bleeding risk. 2, 5