Warfarin Dose Adjustment Recommendation
Yes, increase the warfarin dose immediately—the current INR of 1.9-2.0 is subtherapeutic and places this patient at significantly increased risk of ischemic stroke. 1, 2
Target INR and Current Status
- The therapeutic INR range for atrial fibrillation is 2.0-3.0, with an optimal target of 2.5 to maximize stroke prevention while minimizing bleeding risk. 1, 2, 3
- An INR below 2.0 provides only approximately 80% of the stroke protection achieved with INR 2.0-3.0, representing inadequate anticoagulation. 4, 5
- Patients with INR <2.0 have a 5-fold increased odds of ischemic events compared to those with INR ≥2.0 (OR 5.07,95% CI 2.92-8.80). 5
Dose Adjustment Strategy
Current weekly dose: (6 mg × 6 days) + (7 mg × 1 day) = 43 mg/week
Recommended Approach:
- Increase the total weekly dose by 10-15% (approximately 4-6 mg/week increase) to achieve therapeutic INR. 1
- Practical adjustment: Increase to 7 mg daily for 6 days and 8 mg daily for 1 day (total 50 mg/week), representing a 16% increase.
- Alternative: 6.5 mg daily for 6 days and 7.5 mg daily for 1 day (total 46.5 mg/week), representing an 8% increase if more conservative approach preferred. 1
Monitoring Requirements
- Recheck INR in 1-2 weeks after dose adjustment to assess response and ensure movement toward therapeutic range. 1
- Once therapeutic INR is achieved and stable, monitor at least monthly. 1
- The goal is to maintain time in therapeutic range (TTR) ≥65-70%, ideally ≥70%. 2, 4
Critical Considerations for This Patient
Weight Impact:
- At 181 kg, this patient may require higher warfarin doses than average to achieve therapeutic anticoagulation, though weight is not the primary determinant of warfarin dosing. 1
- The subtherapeutic INR despite current dosing suggests dose requirements are higher than the current regimen provides.
Stroke Risk:
- Atrial fibrillation increases stroke risk 5-fold compared to patients in sinus rhythm, making adequate anticoagulation critical. 1
- The current subtherapeutic INR (1.9-2.0) significantly increases thromboembolic risk without providing meaningful reduction in bleeding risk. 5, 6
Common Pitfalls to Avoid
- Do not accept an INR of 1.9-2.0 as "close enough"—this range provides inadequate stroke protection and should prompt dose adjustment. 5, 6
- Do not use lower INR targets (1.5-2.5) in this patient—moderate quality evidence shows lower targets reduce bleeding but significantly increase thromboembolism (RR 1.50,95% CI 1.29-1.74). 6
- Do not delay dose adjustment—each day at subtherapeutic INR increases stroke risk unnecessarily. 5
- After increasing the dose, ensure follow-up INR testing occurs within 1-2 weeks rather than waiting for routine monthly monitoring. 1