Vitamin K antagonists

Vitamin K antagonists block the liver's use of vitamin K to make clotting factors II, VII, IX, and X. Warfarin prevents and treats blood clots in atrial fibrillation, deep vein thrombosis, pulmonary embolism, and mechanical heart valves. Doses are adjusted to a target INR, bleeding is the main risk, and vitamin K reverses its effect. Many drugs and changes in dietary vitamin K alter its effect, so a consistent intake of leafy greens matters.

• WarfarinKnown brand names include Jantoven and Coumadin.