Anticoagulants are a class of drugs commonly used to prevent the blood from forming dangerous clots that could result in a stroke. Warfarin is an oral anticoagulant. Warfarin differs from most other drugs in that the dosage required to achieve a desired therapeutic effect varies greatly among individuals. Resistance to warfarin has been described as the inability to prolong the prothrombin time or raise the international normalized ratio (INR) into the therapeutic range when the drug is given at normally prescribed doses. However, a higher warfarin requirement does not itself establish the diagnosis of warfarin resistance. Warfarin resistance can be classified as acquired versus hereditary. It can be diagnosed by laboratory studies and can be managed.
Lakshmi R., Anitha, S., N, A. K., and Roshni, P. R., “Warfarin resistance: mechanisms and management”, International Journal of Pharmaceutical Sciences and Research, vol. 3, no. 2, p. 353, 2012.