From the Research
Furosemide (Frusemide) can potentially decrease INR levels in patients taking warfarin, requiring closer monitoring of anticoagulation status, as evidenced by a study showing a 28% decrease in INR after furosemide initiation 1. When furosemide is initiated or its dosage is changed in patients on warfarin therapy, more frequent INR monitoring is recommended, especially during the first week of combined therapy. The effect of furosemide on INR is thought to be due to several mechanisms, including:
- Volume depletion and hemoconcentration, which may decrease the concentration of unbound warfarin in the bloodstream
- Electrolyte disturbances from furosemide, particularly hypokalemia, may also affect warfarin's effects Patients should be advised to watch for signs of decreased anticoagulation such as increased risk of thrombosis. Clinicians may need to adjust warfarin dosing when starting, stopping, or changing furosemide therapy to maintain the target INR range and prevent complications, and consider using low-dose oral vitamin K to stabilize INR levels, as shown in a study where low-dose oral vitamin K decreased INR excursions 2. It is essential to prioritize the single most recent and highest quality study, which in this case is the 2016 study on low-dose oral vitamin K supplementation 2, to guide clinical decision-making and minimize the risk of morbidity, mortality, and decreased quality of life. Key points to consider include:
- Close monitoring of INR levels when furosemide is initiated or changed in patients on warfarin therapy
- Potential need for warfarin dose adjustment to maintain target INR range
- Consideration of low-dose oral vitamin K supplementation to stabilize INR levels
- Patient education on signs of decreased anticoagulation and increased risk of thrombosis.