As stated above INR is ued to regulate coumadin or warfarin therapy The best dose of warfarin (or of any medicine, for that matter) is the lowest dose that accomplishes the desired result.
Considerable research is still going on to determine this dose for warfarin. The problem is difficult because the problems that come with too little warfarin are so bad that it is not ethical to give a dose that has much chance of being too low. On the other hand, higher doses of warfarin are clearly associated with higher risks of major bleeding that can be life-threatening. Current medical thinking relies on the International Normalized Ratio, or INR, of the blood test called the prothrombin time.
The INR is calculated mathematically in a way that corrects for differences in the method used for measuring the prothrombin time. It makes the results more comparable from place to place and at different times in the same place. The INR is a ratio of a clotting time compared to "normal". A normal person would have an INR of about 1.0. People with atrial fibrillation are often told to maintain an INR of 2.0 to 3.0. People with artificial valves and other reasons to have a strong reason to develop dangerous blood thrombi (like clots, but inside the body) are often advised to maintain an INR of 2.5 to 3.5. Newer research suggests that sometimes the INR can be maintained at a lower level (that is, closer to 1.5), but each person should consult his or her own physician about the best INR for him or her.
