Vitamin K Antagonist

Vitamin K Antagonist

Vitamin K antagonists (VKA) are a group of drugs that reduce blood clotting by inhibiting vitamin K epoxide reductase and thus the recycling of vitamin K epoxide back to the active reduced form of vitamin K. These drugs reduce the action of vitamin K by depleting the active form of the vitamin. The term "vitamin K antagonist" is a misnomer, as the drugs don't directly antagonise the action of vitamin K in the pharmacological sense, but rather the recycling of vitamin K. For this reason vitamin K antagonizes the drug's effect (rather than vice versa), and this has led to the loose terminology of vitamin K antagonism.

On the basis of its mechanism of action, the action of this class of anticoagulants in all cases may thus be reversed by administering vitamin K for the duration of the anticoagulant's residence in the body, and the daily dose needed for reversal is the same for all drugs in the class. However, in the case of the second generation "super warfarins" intended to kill warfarin resistant rodents, the time of vitamin K administration may need to be prolonged to months, in order to combat the long residence time of the poison.

The vitamin K antagonists can cause birth defects (teratogens).