vka

VKA stands for vitamin K antagonists, a class of oral anticoagulant drugs that inhibit the action of vitamin K in the liver. By blocking vitamin K epoxide reductase, VKAs reduce the synthesis of vitamin K–dependent coagulation factors II, VII, IX, and X, as well as natural anticoagulant proteins C and S. Onset of full anticoagulation is gradual, often taking several days, and treatment requires regular monitoring of the international normalized ratio (INR) to maintain a therapeutic range.

Common VKAs include warfarin, acenocoumarol, and phenprocoumon. Warfarin is the most widely used in many regions, while acenocoumarol and phenprocoumon are favored in others due to differing pharmacokinetics. Warfarin exists as two enantiomers, with S-warfarin typically more potent than R-warfarin. The dosing of VKAs is individualized and influenced by diet, other medications, and liver function.

Indications for VKAs include atrial fibrillation, venous thromboembolism (including deep vein thrombosis and pulmonary embolism), and prevention of thrombosis in patients with mechanical heart valves. They may also be used after certain surgeries, such as orthopedic procedures, depending on risk.

Reversal and bridging strategies are important in VKAs. In the event of excessive anticoagulation or bleeding, vitamin K (phytonadione) can be given orally or intravenously; for rapid reversal, prothrombin complex concentrates or fresh frozen plasma may be used. In some circumstances, temporary discontinuation of the VKA or bridging with heparin is employed.

DOACs (direct oral anticoagulants) provide alternatives for many nonvalvular indications but are not suitable for mechanical valves; VKAs remain essential in those settings.

Note: VKA can have other, less common meanings in different fields; this article focuses on vitamin K antagonists in medicine.