Extremely Prolonged INR Associated with Warfarin in Combination with Both Trazodone and Omega-3 Fatty Acids

We report the case of a 65-year-old Caucasian male who had been taking warfarin for 6 months after an episode of postoperative pulmonary thromboembolism (PTE). His medical history was otherwise insignificant. He received a prescription of trazodone and fish oil for not-very-well defined complaints. Two weeks after taking these medications, when he routinely checked his international normalized ratio (INR), he arrived at the Emergency Department (ED) with a test result showing an INR of 8.06. He was admitted for observation and all medications were discontinued. His INR returned to normal within 2 days. He was then restarted on his previous warfarin dose, while other drugs were not restarted. Two weeks later, his coagulation profile was within the desired therapeutic range.Coadministration of warfarin with omega-3 fatty acids can lead to additional anticoagulation. This can result from changes either in platelet aggregation or vitamin K-dependent coagulation factors. Trazodone also has interactions with warfarin through not well-understood mechanisms. Although drug interaction reference texts classify warfarin−trazodone interaction as late-onset and clinically insignificant, this has been questioned in other studies. This particular case illustrates a possible interaction between warfarin and these two medications.