Thursday night on "World News," we asked for your questions regarding the new genetic testing recommendations on the labeling of the common blood thinner warfarin, often sold under the brand name Coumadin.
For help in answering your questions, we sought the expertise of Dr. Brian Gage, an associate professor of medicine at the Washington University School of Medicine, who is involved with clinical trials of these genetic tests.
How does the test work?
Question from Kathy of Sloansville, N.Y.:
I started Coumadin about three weeks ago for a blood clot in my calf. Can you explain what is entailed by "genetic testing?" What are they looking for?
Genetic testing can help predict someone's therapeutic dose of warfarin or Coumadin. However, if you've already been taking the anticoagulant for three weeks, then your doctor already knows your approximate therapeutic dose, so genetic testing would not be helpful at this point in your therapy.
How can I find out what genetic tests are needed?
Question from Kim of Tucson, Ariz.:
I am 49 years old and had a blood clot in my leg that moved to my lung a year and a half ago. I have been on warfarin since then and have my blood checked almost every week. I have had a hard time getting adjusted, though, and I have only stayed on a particular dose for two months before having to change doses. How can I find out if this genetic test can help and what tests to get?
Because you've been taking warfarin for so long, genetic testing would not be helpful. Warfarin is affected by changes in your diet and by other medications. I recommend that you get a pill dispenser, which will help ensure that you don't miss a dose, a common reason why it's difficult to regulate warfarin.
What are the long-term side effects of Coumadin?
Question from Diane of Keene, N.H.:
I have been on and off warfarin or Coumadin since I was 20 years old. I am currently on warfarin and will probably be for the rest of my life, as it was determined that I have a blood clotting disorder. My question is, will I have long-term side effects? And if so, should I talk to my doctor about having the genetic testing?
Except for a risk of bleeding, warfarin is remarkably free of side effects. However, we have found that long-term warfarin use can be associated with osteoporosis in elderly men. Although we did not observe this trend in women, as a precaution you should get enough exercise, calcium, and vitamin D to keep your bones strong.
Is long-term use of Coumadin dangerous, and how can I limit the risk?
Question from Bobette of Wildomar, Calif.:
My husband is on 8 mg of warfarin each day after getting DVTs from knee replacement surgery. Should we be concerned at the amount? Will he be on it the rest of his life? There were no details about the use of this drug in the news report. Is long-term use dangerous?
Deep venous thrombosis (DVT) is common after joint replacement surgery and is usually treated with 6-12 weeks of warfarin therapy. However, in certain circumstances, longer duration of anticoagulant therapy is indicated, so your husband should speak with his physician. You should not be concerned about his daily dose of 8 mg as long as his doctor is monitoring his warfarin therapy regularly with an INR blood test.
How do doctors currently determine the proper dose of Coumadin?
Question from Deb of Naples, Fla.:
My mother started Coumadin this week but did not have any prior tests. She was on Lovenox for the past six months, but the cost of it was prohibitive so she was switched to Coumadin. What should we be watching for? How does the doctor currently determine the correct dosage?
Your mother or her doctor can use www.WarfarinDosing.org to help estimate her therapeutic warfarin dose. More commonly, her doctor will adjust the warfarin dose based on regular INR blood testing. During the first weeks of therapy, your mother will likely need to get an INR blood test at least twice per week, but once her INR and dose are stable, she won't need blood testing as often.
Should I be worried about the new recommendations for Coumadin?
Question from Marie of Cumming, Ga.:
I was diagnosed with atrial fibrillation nearly a year ago and was immediately put on Coumadin. After numerous cardioversions, my heart is responding to anti-arrhthymic meds. I feel taking Coumadin is a very risky issue and have wanted to get off of it, but my doctor tells me how I would be very vulnerable to strokes or clotting. My doctor has never discussed any type of gene history with me so I am concerned with this new warning. Is my concern warranted?
No. The genetic testing can identify patients beginning warfarin who have unusual dose requirements, but would not be relevant to you, or others who already taking the anticoagulant.
Are Coumadin and warfarin the same thing?
Question from Sue of Sturgis, S.D.:
I have been on blood thinners for 14 years. My drug plan does not pay for Coumadin, but does pay for warfarin. Is this a safe practice?
Yes, generic warfarin purchased in the U.S. seems safe. We studied 182 patients who switched from Coumadin to a generic warfarin manufactured by Barr. We found no ill effects.
Are these tests for people already on Coumadin, or just for new users?
Question from Arthur of Sheffield, Mass.:
I now take warfarin and have been for three months. My doctor takes a blood test every two weeks and sometime makes adjustments to doses. Should I discuss this genetic test with my doctor, or this only for new startup patients?
The genetic testing won't be helpful for people like you who have already been taking warfarin.
Is there an alternative medication to Coumadin for those with the Factor V gene?
Question from Sharon of Aurora, Ind.:
I am a 53-year-old female, and in February of this year I had two blood clots, one in each lung. I never had these problems before. I was in the hospital for eight days on warfarin. My doctor found out that I have the Factor V gene. I am now on Coumadin, 10 mg a day. Are there any other drugs available that can be used instead of Coumadin? And for anyone who has the Factor V gene, does that mean that they will be on blood thinners for the rest of their lives?
It sounds as if you have bilateral pulmonary emboli, which should be treated with an anticoagulant. Warfarin is the only oral anticoagulant available in the U.S. If you carry one copy of the Factor V gene, then most doctors will treat you for at least six months, and many recommend longer; if you have two copies of this gene, then you should probably remain on warfarin lifelong. Other factors determine how long you should be treated, so check with your doctor. Also, you should avoid estrogen replacement therapy, which can cause a blood clot.
Where can I find more information?
Question from Jay of Grants Pass, Ore.:
The timing of this is perfect. I have an appointment tomorrow to find out about starting me on Coumadin. Where is this information available to find out about "genetic makeup" before prescribing this blood thinner?
The website www.WarfarinDosing.org can help your doctor determine your therapeutic warfarin dose. The new genetic tests (CYP2C9 and VKORC1-1639) are not widely available, but can be ordered from PGXL Laboratories or Kimball Genetics.