Oral anticoagulant

The oral anticoagulants or antivitamines K or AVK are a class of drugs the purpose of which are to inhibit the action of the Vitamine K, vitamin having a role in coagulation, more precisely in the synthesis of the factors of coagulation. This inhibition is made in a competitive way on the K-dependant proteins vitamin.

There exist 2 types of AVK:

coumarinic (Sintrom, Coumadine) the
derivatives of the indanédione (Previscan)

The derivatives of the Coumarine are very employed for this purpose.

The effects of coumarin were discovered by chance: bovines having eaten fermented Trèfle suffered from hemophilia.

The use of AVK is done under regular monitoring of the time of Quick (or Taux of prothrombine), or more often today of the INR (international normalized ratio). The INR, of 1 at the healthy subject, must be maintained between 2 and 4 generally, variable according to treated pathology (between 2 and 3 for the prevention of thrombo-embolic diseases venous MTEV, between 2,5 and 3,5 for the carriers of certain valvular prostheses and the heart cases, and up to 4,5 for certain types of valvular prostheses)

The AVK are prescribed in the situations where a risk of clot is major: obturation of coronary arteries (Myocardial infarction or Angina pectoris), Sténose carotidienne, major venous Thrombosis (phlebitis), etc

Their advantage compared to the other anticoagulants is of being able to be taken by oral way, contrairements with different heparins which must be injected into subcutaneous.

The AVK expose to hemorrhagic phenomena: various hématomes, bleedings (nose, gums,…), brain hemorrhages, etc, particularly in the event of overdose. (INR>5)

The AVK are very much used, because their use is easy, more than the Héparine S which must be used in puncture under cutaneous. On the other hand, their very long half-life being due to their fixing with plasmatic proteins, it is more delicate to reach a stable INR (the effect of the modification of the amount is observed only later).

One uses them mainly in preventive medication, in the event of risk of thromboses: ACFA, cardiac valves mechanical, thrombophilie, etc

They are used in curative treatment of major venous thromboses, of the pulmonary embolisms,… after heparins of low molecular weight.

They are slowly reversible (their antidote is the vitamin K injectable), which makes prefer the injectable anticoagulants in the event of situation at the hemorrhagic risk (surgical operation).

The rich foods in vitamin K (vegetables with green sheets, certain oils, liver, etc) modify their effectiveness. Attention, contrary to the generally accepted ideas, largely spread by the doctors, the tomato is not a rich food in vitamin K, since it contains only 5 µg for tomato 100g, the contributions advised per day being of 45 µg. On the other hand, the French beans contain 22 µg of them. A salad tomato is thus less " dangereuse" that a bundle of French beans…

The AVK are used like Mort in the rats, toxicity residing in the amount, with the result that the amounts mortals for the rodents are not it for the human ones (in the event of ingestion, the vitamin K is the antidote).

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