Causes of Low INR in Patients Taking Warfarin

Patient-Related Factors

• Poor medication adherence or missed doses can lead to low INR in patients taking warfarin, according to the American College of Cardiology 1
• Elderly patients (over 75 years) typically require approximately 1mg/day less warfarin than younger individuals to maintain comparable INR levels, as recommended by the American College of Cardiology 1

Clinical Conditions

• Cancer, particularly certain types, can affect warfarin metabolism, as reported by the Annals of Oncology 2
• For patients with cancer, maintaining therapeutic INR can be particularly challenging, with one study showing INR was within target range only 46% of the time, according to the Annals of Oncology 4

Management Considerations

• Dosage adjustments should be made when INR falls below therapeutic range, as recommended by the American College of Cardiology 3
• When INR is subtherapeutic but patient is not experiencing thrombotic symptoms, increasing the warfarin dose is typically sufficient, according to the American College of Cardiology 3