Warfarin is used to prevent blood clots from forming or growing larger in your blood and blood vessels. It is prescribed for people with certain types of irregular heartbeat, people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. Warfarin is also used to treat or prevent venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung). Warfarin is in a class of medications called anticoagulants ('blood thinners'). It works by decreasing the clotting ability of the blood.

Warfarin is an oral medication in pill form.  The dosage and administration of Warfarin must be individualized for each patient according to the particular patient's PT/INR response to the drug. The dosage should be adjusted based upon the patient's PT/INR

The most serious risks associated with anticoagulant therapy with Warfarin is hemorrhage in any tissue or organ

Call your doctor at once if you have any of these serious side effects:

• skin changes or discoloration anywhere on your body;
• purple toes or fingers;
• pain in your stomach, back, or sides;
• low fever, loss of appetite, dark urine, jaundice (yellowing of the skin or eyes);
• diarrhea, fever, chills, body aches, flu symptoms;
• easy bruising or bleeding that will not stop;
• blood in your urine;
• black, bloody, or tarry stools;
• nosebleeds, bleeding gums, coughing up blood;
• feeling weak or light-headed;
• sudden headache, confusion, problems with vision, speech, or balance;
• sudden leg or foot pain; or
• sudden numbness or weakness, especially on one side of the body.

Less serious side effects may include:

• nausea, vomiting, stomach pain;
• gas and bloating; or
• hair loss.

Warfarin acts by inhibiting the synthesis of vitamin K dependent clotting factors, which include Factors II, VII, IX and X, and the anticoagulant proteins C and S.  Vitamin K is an essential cofactor for the post ribosomal synthesis of the vitamin K dependent clotting factors. The vitamin promotes the biosynthesis of γ-carboxyglutamic acid residues in the proteins which are essential for biological activity.

The price of PT/INR monitoring is a factor that must be considered when determining the total cost of treatment.  Prices vary considerably.