Phytonadione therapy in a multiple-drug overdose involving warfarin

We cared for a patient who ingested an unknown amount of acetaminophen with zopiclone and warfarin. The only liver function test that was abnormal was an increased international normalized ratio (INR), which remained elevated despite treatment with subcutaneous phytonadione and a prolonged infusion of N-acetylcysteine, An interaction between acetaminophen and warfarin may have decreased the hepatic metabolism of warfarin. The patient received num erous antibiotics that may have contributed to the increased INR. The prolo nged elevation of INR also may have been due to infrequent administration o f phytonadione.