Warfarin is a lifesaving drug that doctors love to hate. It has been widely prescribed (mostly as Coumadin) since the mid-1950s to prevent heart attacks and strokes due to blood clots.
No doubt warfarin has prevented a great deal of disease, disability and death. It is also one of the more dangerous drugs in the pharmacy and is responsible for many deaths each year.
How can a drug that is so useful also cause so much trouble? The problem is that it is tricky to use. Getting the dose just right is critical. Too little, and the patient may suffer a blood clot. Too much, and she risks a fatal hemorrhage.
Genetic differences among people affect the amount of drug that is needed. Warfarin also interacts with many foods as well as other drugs.
That's why the effectiveness of the medicine must be monitored on a regular basis. To do this, doctors use a blood test called the INR (international normalized ratio) to tell how much anticoagulation is taking place in the body.
One dilemma patients on warfarin face is how to treat pain such as arthritis. Common analgesics such as aspirin, ibuprofen (Advil, Motrin IB) and naproxen (Aleve) are especially dangerous because they can cause ulcers that then may bleed uncontrollably.
Because of this problem, many doctors recommend acetaminophen (Tylenol) instead. This has become controversial. One reader offered the following:
"I have been on warfarin since developing a blood clot in my leg (deep vein thrombosis) a few years ago. For the past two years or so, I have been checking my coagulation time every two months, and it has been within the proper range.
"I was recently diagnosed with arthritis in my hip, so my doctor put me on Tylenol Arthritis. I've been on the Tylenol for about a month now, and last week my levels were the highest they have been in two years.
"I told my doctor I read in one of your publications that regular use of acetaminophen with warfarin could increase the risk of unwanted bleeding. I asked him if I should have my blood checked more frequently. He said, 'The Graedons are wrong.' What is the source of information for this interaction?"
There seems to be little risk of interaction when acetaminophen (the ingredient in Tylenol Arthritis) is taken only occasionally.
High doses of acetaminophen (2 grams daily) or use for several consecutive days, however, seems to increase the likelihood of a high INR (Blood online, Sept. 12, 2011) and the risk of bleeding (Journal of the American Medical Association, March 4, 1998). The authors of a review of acetaminophen and warfarin warn their medical colleagues that this combination requires extremely close monitoring if it cannot be avoided (Pharmacotherapy, June 2011).
Newer anticoagulants are less likely to interact with other drugs the way warfarin does. They don't require the same level of intense blood monitoring. But drugs such as Eliquis, Pradaxa and Xarelto will be pricey. Instead of $4 a month for warfarin, patients or their insurance companies might pay more than $4 a day.
Preventing deadly blood clots is crucial. Balancing the benefits of the new medicines against their considerable costs will require thoughtful analysis.