Mechanisms

• Antibiotics kills intestinal bacteria that make vitamin K
• Antibiotics inhibit CYP450 enzymes that normally metabolise warfarin

Result

• Increased INR

References

1. Baillargeon, J., Holmes, H. M., Lin, Y., Raji, M. A., Sharma, G., & Kuo, Y.-F. (2012). Concurrent Use of Warfarin and Antibiotics and the Risk of Bleeding in Older Adults. The American Journal of Medicine, 125(2), 183–189. http://doi.org/10.1016/j.amjmed.2011.08.014