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Drug interactions with vitamin K antagonist may involve antiepileptic drug. Numerous antiepileptic drugs are strong inducers or inhibitors of liver enzymes and affect warfarin metabolism, including valproic acid, which is capable of displacing warfarin from the protein binding site. Although this type of drug interaction is less widely recognized, it is a phenomenon that causes significant changes in the INR. We report a case of severe subconjunctival bleeding in patient with concomitant use of warfarin and valproic acid. The management include cessation of the drug, conservative eye treatment, and vitamin K. The case was fully resolved.