Indications
Farin is indicated for prophylaxis and/or treatment of thromboembolic complications associated with atrial fibrillation and/or cardiac valve replacement. It is also indicated to reduce the risk of death, recurrent myocardial infarction, and thromboembolic events such as stroke or systemic embolization after myocardial infarction, for prophylaxis and treatment of venous thrombosis and pulmonary embolism, and for transient ischaemic attacks.
⚠️ Always consult a registered physician before taking any medicine.
Pharmacology
Warfarin works by blocking vitamin K, a vitamin the body needs to make several clotting proteins. It does this by inhibiting vitamin K epoxide reductase, the enzyme that recycles vitamin K. Once the enzyme is blocked, the body cannot turn vitamin K back into its active form.
The active form, vitamin KH2, acts as a cofactor in the γ-carboxylation of coagulation factors VII, IX, X and thrombin. This carboxylation changes the shape of the factors so they can bind Ca2+ and attach to phospholipid surfaces. Factors VII, IX, X and thrombin that have not been carboxylated are biologically inactive, which is how they interrupt the coagulation cascade. Proteins C and S, the body's own anticoagulant proteins, also need γ-carboxylation to work. This matters most for thrombin, which must be activated before it can form a thrombus.
During the γ-carboxylation reaction, which is catalyzed by γ-glutamyl carboxylase, vitamin KH2 is converted to vitamin K epoxide. Vitamin K epoxide is then changed to vitamin K1 by vitamin K epoxide reductase, and vitamin K1 goes back to vitamin KH2 through vitamin K reductase. Warfarin binds to vitamin K epoxide reductase complex subunit 1 and inhibits the enzyme irreversibly. This stops the recycling of vitamin K, because vitamin K epoxide can no longer be converted to vitamin K1.
At first, this creates a short period in which the blood is more likely to clot. Proteins C and S break down first, with half-lives of 8 and 24 hours, and factor VII follows with a half-life of 6 hours. Factors IX, X and finally thrombin break down later, with half-lives of 24, 36 and 50 hours. It is this later drop that produces the main anticoagulant effect.
To reverse the anticoagulation, vitamin K has to be supplied, either from outside the body or by removing the blockage on vitamin K epoxide reductase. Then the body needs time to make new coagulation factors. In the liver, this takes about 2 days.
Vitamin K2 is functionally the same as vitamin K1, but it is made by bacteria in the gut. This is why antibiotics can affect it, since killing these bacteria can lower the body's vitamin K2.
Pregnancy & Breastfeeding
PREGNANCY & BREASTFEEDING
Warfarin must not be used during the first trimester of pregnancy, as it carries a risk of birth defects (teratogenicity). More broadly, it should be avoided in women who are pregnant or who may become pregnant, since the drug crosses the placenta and can cause fatal bleeding in the fetus.
In breastfeeding, warfarin passes into breast milk, but only in an inactive form. Studies of infants breastfed by mothers taking warfarin have shown no change in their prothrombin time. However, its effects on premature infants have not been studied.
⚠️ Talk to your doctor before taking any medicine during pregnancy or while breastfeeding.
Dosage Reference
⚠️ Reference ranges from official sources only. Consult your doctor for personalized dosing.
Side Effects & Interactions
Side Effects
No side-effect data recorded yet.