Background: Warfarin is affected by many variables such as diet, alcohol, and medications; however, it is unclear if brand to generic conversion may also play a role. This case reports a patient with fluctuating international normalized ratio (INR) while being switched from brand to generic temporarily. Case Presentation: A 60-year-old obese white male taking brand name Jantoven© (warfarin) at home for 9 years at a consistent dose for atrial fibrillation was in hospital for treatment of cellulitis. He was switched to generic warfarin at his home dose on admission. While in hospital, he required dose escalation to three times his home dose to achieve a therapeutic INR. Conclusion: Generic warfarin may have different effects on INR when compared to brand name Jantoven©. More research is warranted to determine if differences may truly exist and potential ways to address the issue. Until then, providers should be cognizant of interchanging the two products to monitor for INR variation.

Keywords: Jantoven, warfarin, inpatient, atrial fibrillation, substitution, INR.