Thank you for your recent inquiry.
True allergy reactions to Coumadin are extremely rare. The only recent reference that I could find appeared in Cardiology(1). In this case, the patient was skin tested and desensitized. The reference is listed below. This article also has two references to previously reported allergy or "allergy-like" reactions to this drug, and contains a protocol for skin testing and desensitization.
Thank you again for your inquiry and we hope this response is helpful to you.
(1) Jameson DS: Induction of Tolerance to Warfarin after Anaphylaxis with a Desensitization Protocol. Cardiology 2010; 115: 175-5
Phil Lieberman, M.D.