Practical issues with vitamin K antagonists: elevated INRs, low time-in-therapeutic range, and warfarin failure

Millions of patients worldwide are prescribed vitamin K antagonists for a variety of medical conditions annually. Despite widespread and long-standing experience with these medications, medical care providers are often confronted with challenging clinical situations. Vitamin K antagonists have a narrow therapeutic index secondary to intrinsic patient characteristics and extrinsic factors including a propensity for drug–drug interactions. …