VKA

The vitamin K antagonists (VKA) belong to the family of oral anticoagulants. They are widely prescribed to treat phlebitis, pulmonary embolism and some cardiac dysrhythmias, and require close medical supervision.

How do the vitamin K antagonists or VKA work?

Vitamin K controls the production by the liver of different coagulation factors (factors II, VII, IX, and X) and proteins which are also involved in blood coagulation. The VKA are therefore intended to reduce the production of these coagulation factors in order to thin the blood and prevent thrombus (clot) formation.

Do they have contraindications or precautions?

Although widely used, the VKA are difficult medicines to mange. They vary in efficacy between patients, depending on many factors:

• co-existence of other diseases;
• other medicines taken;
• diet: vitamin K is contained in many foods, including broccoli, spinach, lettuce and... coffee. These must therefore be avoided by patients taking VKA in order to avoid reducing the anticoagulant effect.

The effective dose of VKA required for each patient is difficult to establish. In order to assess the action of these medicines on blood thinning, doctors use the INR (International Normalised Ratio). This is measured from blood samples taken regularly during treatment, which places a real demand on patients. Doctors watch particularly for the risk of bleeding with the VKAs. For this reason, the INR must not be too high (a sign that the treatment is certainly being effective, but carries a significant risk of bleeding), or too low.

Source: Interview with Dr Yannick Béjot, (Dijon University Hospital), 15 June 2011