Vitamin K antagonist

Warning label on a tube of "brown rat" poison laid on a dike of the Scheldt river in Steendorp, Belgium. The tube contains bromadiolone, a second-generation (superwarfarin) anticoagulant. The label in Dutch states, in part: Contains an anticoagulant with prolonged activity. Antidote Vitamin K1.
Vitamin K2 (menaquinone). In menaquinone the side chain is composed of a varying number of isoprenoid residues.

Vitamin K antagonists (VKA) are a group of substances that reduce blood clotting by reducing the action of vitamin K. The term "vitamin K antagonist" is technically a misnomer, as the drugs do not directly antagonize the action of vitamin K in the pharmacological sense, but rather the recycling of vitamin K. Vitamin K antagonists (VKAs) have been the mainstay of anticoagulation therapy for more than 50 years.

They are used as anticoagulant medications in the prevention of thrombosis, and in pest control, as rodenticides.