Objective
To present two cases of probable warfarin and baclofen interactions which occurred during the concomitant drug administrations.

Case Summary: In the first case, a 55-year-old man with C6 ASIA C receiving 80 mg/day of baclofen was prescribed 5 mg/day of warfarin after heparinization for the treatment of deep vein thrombosis of the left external iliac vein. After the third day of warfarin administration, the patient exhibited cognitive dysfunction. Within one week after initiation of warfarin, the INR increased to 4.4, with increased cognitive dysfunction. After the stop of warfarin, the return of the INR to baseline took six days. In the second case, a 45-year-old man with a spastic right hemiplegia from a stroke and a history of myocardial infarction was on 5 mg/day of warfarin for two years. When forty-five mg of baclofen was added, the patient developed a nausea, fatigue, and confusion after three days. The INR increased to 4.5 at eight days after the baclofen was added, despite the diminished dosage of warfarin.

Conclusion
These two cases suggest a probable warfarin-baclofen interaction. Attention should be given to the patients who concomitantly use the warfarin and baclofen to protect the patient from harmful drug interactions.