Should I adjust the warfarin (anticoagulant) dose for a patient with a subtherapeutic International Normalized Ratio (INR) of 1.82, currently taking 2.5mg twice a week?

From the Guidelines

You should increase the warfarin dose for this patient with a subtherapeutic INR of 1.82 who is currently taking 2.5mg twice weekly, as the current INR is below the therapeutic range of 2.0-3.0. According to the 2018 European Heart Rhythm Association practical guide on the use of non-vitamin K antagonist oral anticoagulants in patients with atrial fibrillation 1, for an INR of 1.6-1.9, the recommended dose adjustment is an increase by 10%/week. A modest dose increase of approximately 10% would be appropriate, such as increasing to 2.75mg twice weekly. After making this adjustment, schedule an INR recheck in 1-2 weeks to assess the response. The patient's diet, medication changes, and adherence should also be assessed, as vitamin K intake, drug interactions, and missed doses can all affect INR values. If the patient has recently started warfarin or has had multiple subtherapeutic readings, more frequent monitoring may be necessary until stable therapeutic levels are achieved. It is also worth noting that the evidence from the American College of Chest Physicians evidence-based clinical practice guidelines 1 suggests that for INRs between 1.7 and 3.3, warfarin doses may not need to be changed, but in this case, the patient's INR is below the therapeutic range, making a dose adjustment necessary to minimize the risk of thrombotic events. Key considerations in warfarin dose adjustment include:

• Gradual dose changes to avoid overshooting the target range and causing bleeding complications
• Regular monitoring of INR levels to assess the response to dose adjustments
• Assessment of patient factors that may affect INR values, such as diet, medication changes, and adherence.

From the Research

Warfarin Dose Adjustment

The patient is currently taking 2.5mg of warfarin twice a week, resulting in a subtherapeutic International Normalized Ratio (INR) of 1.82. To determine if a dose adjustment is necessary, we can consider the following points:

• The target INR range for most patients on warfarin is between 2.0 and 3.0, as stated in 2.
• An INR of 1.82 is below the therapeutic range, which may indicate an increased risk of thromboembolic events.
• According to 3, adjusting a steady-state warfarin dose depends on the measured INR values and clinical factors. The dose does not need to be adjusted for a single INR that is slightly out of range, and most changes should alter the total weekly dose by 5% to 20%.
• A study published in 4 suggests that in stable patients on warfarin with an occasional INR outside the therapeutic range, it seems reasonable to continue with the same dose without a single-dose change and perform a repeat test in about 2 weeks.

Considerations for Dose Adjustment

Some key considerations for dose adjustment include:

• The patient's current INR value and the degree to which it deviates from the target range.
• The patient's clinical factors, such as their medical history, age, and other medications.
• The potential risks and benefits of adjusting the warfarin dose, including the risk of bleeding and thromboembolic events.
• The results of previous studies, such as those published in 5 and 6, which demonstrate the importance of maintaining a therapeutic INR range to prevent thromboembolic events.

Potential Course of Action

Based on the available evidence, potential courses of action could include:

• Increasing the warfarin dose to achieve a therapeutic INR range, as suggested in 3 and 2.
• Maintaining the current dose and monitoring the patient's INR values closely, as suggested in 4.
• Considering alternative anticoagulant therapies, such as those discussed in 6, if the patient is at high risk of thromboembolic events or has a history of bleeding complications.