In an elderly patient on warfarin (Coumadin) with recent missed doses and poor oral intake, whose INR is 2.9 after a 1 mg dose this morning, when should the INR be rechecked and should any warfarin be given tonight?

Management of Warfarin in an Elderly Patient with Recent INR Fluctuations and Poor Oral Intake

Tonight's Warfarin Dose

Hold warfarin tonight (Monday evening) and recheck INR tomorrow morning (Tuesday). 1, 2

The current INR of 2.9 falls within the therapeutic range of 2.0–3.0, but this patient has demonstrated marked warfarin sensitivity with recent supratherapeutic INRs (3.5 and 4.0) and has had poor oral intake—a critical factor that increases bleeding risk and warfarin effect in elderly patients. 1 The American Geriatrics Society specifically recommends withholding warfarin when INR values have been recently elevated and the patient has high-risk features such as advanced age and nutritional compromise. 1

INR Monitoring Schedule

• Recheck INR Tuesday morning (24 hours after the 1 mg dose) to assess the trajectory of INR change and ensure it remains stable within the therapeutic range. 1, 3

• If Tuesday's INR is 2.0–3.0, continue daily INR monitoring for the next 2–3 days given the recent instability and poor oral intake. 1

• Once INR stabilizes in the therapeutic range for 2–3 consecutive days, transition to checking INR 2–3 times weekly for 1–2 weeks, then weekly for 1 month. 1, 3

Resuming Warfarin Therapy

When to restart: Resume warfarin only after confirming that:

• The patient's oral intake has improved and stabilized 1
• INR remains stable in the 2.0–3.0 range for at least 24–48 hours 2, 4
• No new medications (especially antibiotics) have been introduced 1

Maintenance dose recommendation: Start with 1–2 mg daily when resuming therapy. 1, 5

Elderly patients typically require maintenance doses of 2–4 mg daily rather than the standard 5 mg, and this patient has demonstrated marked dose-response sensitivity with significant INR elevation on 5 mg doses. 1, 5 The American Geriatrics Society recommends reducing the weekly warfarin dose by 20–30% after a supratherapeutic INR episode. 1

Critical Factors Driving This Recommendation

Poor oral intake is the key concern. Reduced food intake in elderly patients decreases vitamin K absorption, potentiating warfarin's anticoagulant effect and increasing bleeding risk even at therapeutic INR values. 1 This patient's INR rose from 2.9 to 3.5 and then to 4.0 despite dose reductions, suggesting either:

• Ongoing poor nutrition with decreased vitamin K intake 1
• Warfarin accumulation due to age-related pharmacokinetic changes 1, 5
• Unidentified drug interactions or intercurrent illness 1

Age amplifies bleeding risk. Patients over 65 years have exponentially higher bleeding risk at any given INR level, with clinically significant risk beginning at INR >3.5. 1, 2 This patient's recent INR of 4.0 placed them in a high-risk category even without active bleeding. 2

Investigation Before Next Dose

Before administering any further warfarin, systematically evaluate:

• Medication changes: New antibiotics are the most common cause of unexpected INR elevation in elderly patients. 1 Review all medications including over-the-counter drugs and herbal supplements. 1

• Dietary assessment: Quantify current oral intake and recent changes in vitamin K consumption (green vegetables, nutritional supplements). 1 Poor oral intake dramatically increases warfarin sensitivity. 1

• Intercurrent illness: Fever, diarrhea, or acute illness can alter warfarin absorption and metabolism. 1 Dehydration from poor fluid intake may concentrate warfarin levels. 1

• Hepatic and renal function: Changes in liver or renal function are especially relevant in older adults and can modify warfarin metabolism. 1

Common Pitfalls to Avoid

Do not give warfarin tonight simply because INR is "therapeutic." The recent pattern of supratherapeutic INRs (3.5 → 4.0) combined with poor oral intake indicates this patient is at high risk for INR overshoot with any additional dose. 1, 2 The half-life of warfarin means the 1 mg dose given this morning will continue exerting anticoagulant effect for 2–7 days. 1, 6

Do not administer vitamin K. Vitamin K is not indicated for an INR of 2.9 without bleeding and would create warfarin resistance, making re-anticoagulation difficult once oral intake improves. 1, 2 Vitamin K is reserved for INR >5.0 in asymptomatic patients or any INR with active bleeding. 2, 4

Do not resume the previous 5 mg dose. This patient requires a much lower maintenance dose (likely 1–2 mg daily) based on their demonstrated sensitivity and elderly status. 1, 5 Elderly patients often achieve stable anticoagulation with 2–3 mg daily rather than standard 5 mg dosing. 1

Expected Maintenance Dose

Based on this patient's marked sensitivity (INR 4.0 on recent 2 mg dose) and advanced age, the eventual maintenance dose will likely be 1.5–2.5 mg daily. 1, 5 The American Geriatrics Society notes that elderly patients demonstrating this degree of dose-response sensitivity typically require maintenance doses in this range. 1