Warfarin Dosing for INR 2.9
Continue the current warfarin dose of 12 mg weekly without modification and recheck the INR in 1–2 weeks. 1
Rationale for No Dose Adjustment
An INR of 2.9 falls within the standard therapeutic range of 2.0–3.0 for atrial fibrillation, prior ischemic stroke, and venous thromboembolism (DVT). 2, 3 This single measurement does not warrant dose reduction, as clinically significant bleeding risk does not increase appreciably until the INR exceeds 3.5. 4, 1
For today's specific dose: Give the patient his usual daily warfarin amount, which is approximately 1.7 mg per day (12 mg ÷ 7 days). 2
When to Consider Dose Reduction
Reduce the weekly warfarin dose by approximately 10% only if: 1
- The INR remains persistently >3.0 on multiple consecutive measurements
- The INR exceeds 3.5
- The patient develops additional high-bleeding-risk factors (though at age 81, advanced age is already present) 4, 1
Monitoring Schedule
- Recheck INR in 1–2 weeks to verify stability within therapeutic range 1
- Once stable, continue monitoring every 4 weeks 2
- If any dose adjustment becomes necessary, resume more frequent monitoring (weekly) until the INR stabilizes again 2
Critical Pitfalls to Avoid
Do not administer vitamin K at an INR of 2.9—vitamin K is reserved for INR values >5.0 in asymptomatic patients or for active bleeding scenarios. 4, 1 Giving vitamin K at this therapeutic INR level can induce warfarin resistance and make re-anticoagulation difficult. 4
Do not reduce the dose based on a single measurement in the therapeutic range, as this increases the risk of subtherapeutic anticoagulation and subsequent thromboembolism. 5, 3 The risk of ischemic stroke rises sharply when INR falls below 2.0 in patients with atrial fibrillation and prior stroke. 6, 3
Investigation of INR Stability
Systematically evaluate potential contributors to any INR fluctuation: 1
- Recent medication changes (especially antibiotics, acetaminophen >2 g/day)
- Alterations in dietary vitamin K intake
- Intercurrent illness affecting hepatic or renal function
- Medication adherence
Special Considerations for This Patient
At age 81 with multiple indications for anticoagulation (atrial fibrillation, prior ischemic CVA, history of DVT), maintaining therapeutic anticoagulation is critical. 6, 3 Elderly patients have increased bleeding risk, but the benefits of maintaining INR 2.0–3.0 outweigh the risks in patients with these high-risk thromboembolic conditions. 6, 3
The current weekly dose of 12 mg is relatively low and appropriate for an elderly patient, as those over 65 years typically require lower maintenance doses (<5 mg daily). 2