A65-year-old male patient with known atrial fibrillation on long-standing coumadin therapy is being seen in the clinic today for a sudden drop in his inr. the inr isn't in a therapeutic range for the treatment of the a-fib. the nurse has reviewed the patient's history and current list of medications. it's noted that the patient has started taking a multi-vitamin supplement that contains vitamin k, and he's trying to eat healthy. patient reports eating a green, leafy salad every day for the last 2 weeks. the physician determines that the sudden increase in vitamin k intake has decreased the effectiveness of the coumadin. what's this correlation called?