From the Guidelines
The warfarin dose should not be adjusted at this time, and the patient's INR should be rechecked in 1 to 2 weeks to exclude a progressive deviation from the therapeutic range. The current INR of 2.2 is slightly below the target range of 2.5-3.5 for this 60-year-old male with an aortic valve replacement, but the evidence suggests that small deviations from the therapeutic range do not necessarily require immediate dose adjustments 1. According to a study published in Chest, results were similar at follow-up 2 weeks later, with 44% outside the therapeutic range among patients randomized to a one-time dose change compared with 40% of those randomized to no dose change (OR, 1.17; 95% CI, 0.59-2.30; P 5 .75) 1.
Some key points to consider in this decision include:
- The patient's current regimen of 7.5 mg on Tuesday and Friday with 5 mg on Sunday, Monday, Wednesday, Thursday, and Saturday has been effective in maintaining INRs within a relatively stable range.
- The evidence from both studies suggests that warfarin doses do not need to be changed for INRs between 1.7 and 3.3, which includes the patient's current INR of 2.2 1.
- A dosing model developed from an observational study of 3,961 patients also supports this approach, suggesting that warfarin doses do not need to be changed for small deviations from the therapeutic range 1.
- It is reasonable to follow up with an INR after 1 to 2 weeks to exclude a progressive deviation from the therapeutic range, rather than making immediate dose adjustments 1.
From the FDA Drug Label
For all patients with mechanical prosthetic heart valves, warfarin is recommended. For patients with a St. Jude Medical (St. Paul, MN) bileaflet valve in the aortic position, a target INR of 2.5 (range, 2.0 to 3. 0) is recommended. For patients with tilting disk valves and bileaflet mechanical valves in the mitral position, the 7th ACCP recommends a target INR of 3.0 (range, 2.5 to 3.5).
The patient's current INR of 2.2 is below the target range of 2.5 to 3.5 for a patient with an aortic valve replacement. The patient's warfarin dose may need to be adjusted to achieve the target INR range. 2
From the Research
Patient Information
- The patient is a 60-year-old male with an aortic valve replacement.
- The patient's current INR is 2.2, which is below the target range of 2.5 to 3.5.
- The patient's warfarin dosing schedule is as follows: 7.5 mg on Tuesdays and Fridays, and 5 mg on Sundays, Mondays, Wednesdays, Thursdays, and Saturdays.
Warfarin Dosing Adjustments
- According to the study by 3, adjusting a steady-state warfarin dose depends on the measured INR values and clinical factors, and most changes should alter the total weekly dose by 5% to 20%.
- The study by 4 suggests that for asymptomatic patients with an INR of ≤ 3.3, the warfarin dose does not need to be adjusted, and reducing the dose for patients who have a greater INR or an increased risk of hemorrhage is recommended.
- The study by 5 found 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.
Factors Influencing Warfarin Dose Response
- The study by 6 highlights the importance of considering patient factors that influence warfarin dose response, including age, body weight, nutritional status, acute and chronic disease states, and changes in concomitant drug therapy and diet.
- The study by 7 found that age > 65 years, body mass index < 24 kg/m2, and initial warfarin dose ≥ 3 mg/d were independent factors associated with rapidly achieving the first therapeutic INR target of warfarin therapy.
Potential Next Steps
- Consider monitoring the patient's INR more frequently to determine if the current dose is effective in achieving the target range.
- If the patient's INR remains below the target range, a dose adjustment may be necessary, taking into account the patient's individual factors that influence warfarin dose response, as suggested by 3, 4, and 6.