Warfarin is a wonderful and dangerous drug. We use it for atrial fibrillation, cardiac thrombi, deep vein thrombi, and pulmonary emboli. I always have a difficult time explaining warfarin (aka Coumadin) to patients. Perhaps this article will help – Patients on Anticlotting Drug Face a Tricky Balancing Act
As with all NY Times links, this link converts to an opportunity to pay for the article eventually (I think a month). Many physicians may want to print out this article to distribute to patients. Let me include this quotation:
But warfarin, as well as its generic mimics, is a tricky lifesaver, with a narrow margin of safety and effectiveness. Too little and it cannot do the job of preventing life-threatening blood clots. Too much and it can cause very serious and even fatal bleeding. Everyone on warfarin must be faithful about taking the right dose at the right time and having clotting times monitored at predetermined intervals.
“Patients who take warfarin (Coumadin) walk a tightrope between bleeding and clotting ? and a hundred things can tip the balance,” Dr. Amir Jaffer, a hematologist, and Dr. Lee Bragg, a pharmacologist, wrote in the April issue of The Cleveland Clinic Journal of Medicine. “It’s a difficult drug to use, with a narrow therapeutic index, but 60 years after it was introduced, it is still the mainstay of oral anticoagulation treatment.”
Dr. Jaffer is medical director and Dr. Bragg is coordinator of the Anticoagulation Clinic at the Cleveland Clinic. They pointed out that only a minority of patients taking warfarin were managed by anticoagulation clinics, where the risk of excessive bleeding or unwanted clots is significantly lower.
Warfarin began its life at the University of Wisconsin as a highly effective rat poison. It works to inhibit clotting of the blood by interfering with the production of clotting factors that depend on vitamin K.
It was named warfarin for the Wisconsin Alumni Research Foundation (WARF), which supported its development.
In neighborhoods where warfarin is used to control rats, warnings are posted to protect pets and children from exposure, along with the recommended antidote, the coagulation promoter vitamin K, in case a nontarget animal is affected.
If I needed warfarin, I would become extremely compulsive about checking my blood work. We follow the INR as the following quote explains:
The goal is a measurement called the international normalized ratio, or I.N.R., a measure of how fast the patient’s blood clots, or prothrombin time, is in relation to the average clotting time for people who are not taking anticoagulants. For most patients, the desired I.N.R. range is from 2 to 3.
The key here as that a higher INR increases the probability of bleeding, and a lower INR increases the probability of clotting. Thus we do have a tightrope analogy.
