Coumadin (warfarin) is a medication commonly used for the treatment of atrial fibrillation. It is also used in the treatment of other disorders such as deep venous thrombosis (DVT), embolic strokes, artificial heart valves, pulmonary embolus (blood clot to the lungs), and other conditions. Coumadin affects the coagulation system and is considered an anticoagulant (blood thinner). It affects Vitamin K dependent clotting factors in the blood stream. Many medications, foods and illnesses can affect Vitamin K dependent blood factors, which can alter absorption and efficacy of Coumadin. Following administration of this drug, individuals are monitored closely with an international normalized ratio (INR). The great difficulty with Coumadin is that it works within a narrow therapeutic window. An INR of less than 2 results in very little, if any, prevention of blood clotting in the body. An INR of greater than 3.5 – 4.0 leads to greater incidents of bleeding complications. In order to best manage Coumadin, the levels have to be checked frequently and the dosage adjusted carefully. Both patients and physicians alike can become frustrated with the management of Coumadin because the INRs will appear to have “a mind of their own”. Illness, antibiotics, drug interactions, the timing of the medication, and other factors can affect the ability to achieve the proper INR. For example, a multivitamin containing Vitamin K can result in a subsequently lower INR than expected in a patient who has been stable for years. Therefore, doctors and patients alike have to work together to achieve the proper goal.
In most individuals treated with warfarin, the INR goal is a range from 2.0 to 3.0. However, a range of 2.5 – 3.5 and slightly higher may be recommended in certain individuals (for example, a patient with a previous stroke on Coumadin or a mechanical mitral valve). It is very important that every patient know the goal for his or her INR. It is recommended that the INR be checked at least every four weeks. However, depending upon the circumstance, the INR may need to be checked more frequently, particularly with changes in the medication dose or initiation of therapy. When a patient on Coumadin experiences excessive bleeding or bruising, the INR should be evaluated and the patient examined. Prior to elective surgery, the Coumadin is usually stopped several days before. In many instances, the Coumadin will be bridged with subcutaneous blood thinner. This is particularly true in high-risk patients such as those with clotting deficiencies and prosthetic heart valves.
The goal with Coumadin therapy is to prevent blood clots which can subsequently result in stroke, incapacitation, or death. Since the drug has a narrow therapeutic window, individuals need to be evaluated closely and the drug adjusted carefully. The physician, nurses, and patient must work as a team in order to achieve the best dose with the fewest complications. Should you ever have any questions regarding Coumadin or its potential side effects and drug interactions, we will be more than happy to assist you.