A clinically significant drug interaction between warfarin and amoxicillin resulting in persistent postoperative bleeding in a dental patient.

One of the few cases reported in the literature, this article reviews the case of a 66-year-old man who developed an elevated international normalized ratio and sustained clinically significant bleeding as a result of a drug-drug interaction between warfarin and amoxicillin. Given the popularity of these medications, it is surprising that these reports are not more commonplace, and there is a concern that the lack of reports may result in practitioners overlooking the significance of this possible complication. Although the mechanism for this interaction is not fully known, it is suspected that a decrease in vitamin K-producing gut flora, with resulting vitamin K deficiency, is the most likely contributing factor. An objective causality assessment revealed that this adverse drug event, secondary to the warfarin and amoxicillin interaction, was probable.