Download Coumadin Interactions

Graedons’ Guide to
Coumadin Interactions
Some of our most important medicines have been discovered almost by accident. Coumadin
(warfarin) is a classic example. In the early 1900s, Dakota farmers started using sweet clover to feed their
cattle because it grew well under difficult conditions. But in the ’20s, cattle that ate spoiled clover silage
developed a severe bleeding disease. Scientists tracked the cause of the problem to an ingredient of
clover, dicoumarol. They developed a synthetic derivative, warfarin, initially for use as rat poison. In
the 1950s doctors realized that this compound could be used to prevent blood clots in humans.
Millions of people now take Coumadin regularly to prevent dangerous blood clots in the legs, lungs,
heart or brain. This anticoagulant medicine is a life-saver for people prone to such clots, especially those
with irregular heart rhythms (atrial fibrillation) or other conditions that predispose them to this kind
of problem.
Getting the dose right is essential in using Coumadin successfully. Too low a dose and a person can
run the risk of thrombophlebitis, pulmonary embolism, heart attack or stroke. But if the dose climbs too
high, there is an increasing possibility of hemorrhage, which can also be life-threatening.
To help them keep their patients on this tightrope, doctors measure blood clotting potential (called
prothrombin time, or PT) periodically. At first, PT should be measured every day or two. But even
patients stabilized on Coumadin should have PT monitored every 4 to 6 weeks. Daily monitoring is also
desirable any time a new drug is added or an old one dropped. The doctor will use values for the PT
and the International Normalized Ratio (INR), calculated from the PT, to adjust the dose of Coumadin
if necessary. Although each situation is different, the doctor will usually aim for an INR between 2 and
3. If the INR climbs above 4 there is a risk of serious hemorrhage.
Many drugs can affect the activity of Coumadin. Most patients are warned to avoid aspirin, which
increases the risk of hemorrhage. As few as four regular strength (325 mg) acetaminophen tablets daily
over the course of a week or more can dramatically increase the risk of a high INR (JAMA, March 4,
1998). Since acetaminophen is found in hundreds of OTC and prescription products (Tylenol is best
known), anyone on Coumadin must be extremely vigilant. Because the artifical sweetener aspartame
(NutraSweet) increases bleeding time on its own (Clin. Pharmacol. Ther., Feb. 1998), it too should be used
with caution by people taking Coumadin. Here is a partial list of medications that may alter
Coumadin's effectiveness. If you must take one of them, please check with your physician and
pharmacist. Never start or stop any medicine without medical supervision.
acetaminophen
Achromycin V
Advil
Aleve
Alka-Seltzer
Anacin
Ansaid
Antabuse
Ascriptin
aspirin
Bactrim
barbiturates
Biaxin
Cardioquin
co-trimoxazole
Colestid
Cordarone
© 1998 Graedon Enterprises, Inc.
Danocrine
Diflucan
Dilantin
E-Mycin
E.E.S.
Ecotrin
ERYC
EryPed
EryTab
Erythrocin
flu vaccine
Feldene
Flagyl
Ilosone
Indocin
Lodine
Lopid
male hormones
Mevacor
Monistat
Motrin
Naprosyn
Nizoral
Nolvadex
Nuprin
Paxil
PCE
Pediazole
phenytoin
Propulsid
Protostat
Prozac
Questran
quinidine
Quinora
Relafen
rifampin
Septra
SMZ-TMP
Sporanox
Tagamet
tamoxifen
Tao
Tegretol
tetracycline
thyroid hormone
Toradol
Vibramycin
Voltaren
Zithromax
Zoloft
Many people forget that alcohol is a drug and
it can affect Coumadin. Alcohol is complicated,
however, because modest intake has a different
impact on bleeding time than heavy drinking.
Grapefruit or grapefruit juice may also alter PT
values. Illness that involves diarrhea or vomiting which can lead to dehydration may increase
the potency of Coumadin.
Diet is one of the most complicated factors in
Coumadin management. Because this drug
works by counteracting vitamin K, essential for
coagulation, it is important to keep vitamin K
intake relatively stable. Too much vitamin K in
the diet could reduce the benefits of the drug and
lead to a blood clot. People should not avoid
vitamin K-rich foods, but they should be careful
not to deprive themselves all week and suddenly overindulge. One woman ended up in the
hospital with a pulmonary embolism because
she binged on collard greens over the weekend.
The RDA for normal healthy people is 0.5 to 1
microgram (mcg) of vitamin K per kilogram [2.2
lb] of body weight. This means that appropriate
vitamin K intake be at least 25 mcg to 45 mcg of
vitamin K daily for a small person of about 100
pounds. A larger person weighing 180 pounds
should get a minimum of 40 mcg to 80 mcg
vitamin K daily. For a person on Coumadin the
most important factor is not to vary vitamin K
intake much from day to day. Keeping track of
your diet and your PT and INR values will allow
you and your physician to adjust your dose of
Coumadin properly.
For example, a person striving for 75 mcg of
vitamin K daily might eat cereal with a glass of
milk (10 mcg) for breakfast and have tuna (24
mcg) in a salad with celery (32 mcg) for lunch.
The next day, this person might have a serving
of cole slaw (52 mcg) at lunch and a half-cup of
green peas (24 mcg) at dinner. Unfortunately,
the tables we consulted from the manufacturer
of Coumadin and Bowes & Church's Food Values
of Portions Commonly Used, 17th edition, did not
agree in each case. We have indicated discrepancies with an asterisk (*) and given both values.
The key to successful anticoagulant therapy
is regular blood testing. Too much Coumadin
can lead to hemorrhage. Alert your physician
immediately if you experience: easy bruising;
unusual bleeding, including blood in stool, urine
or around the gums; nosebleeds; or excessive
menstrual bleeding.
FOOD SOURCES OF VITAMIN K
Foods
Vitamin K in mcg
Vegetables:
Asparagus (1 spear)*
Bean sprouts, raw (1/2 cup)
Broccoli, cooked (1/2 cup)*
Brussels sprouts (5 sprouts)
Cabbage, raw (1/2 cup shredded)
Cabbage, cooked (2/3 cup)
Cauliflower, raw (1/2 cup)
Chick peas, dry uncooked (1 ounce)
Celery, raw (2 1/2 stalks)
Collards, cooked (1/2 cup)
Endive, raw (1 cup)
Green beans (3/4 cup)
Kale, raw (3 1/2 ounces)
Lentils, uncooked (1 ounce)
Lettuce, bibb (1 ounce)
Lettuce, red leaf (1 ounce)
Lettuce, iceberg (5 leaves)
Mung beans, uncooked (1 ounce)
Okra, sliced and cooked (1/2 cup)
Parsley, raw (1/2 cup)
Peas, split, uncooked (1 ounce)
Peas, green, cooked (1/2 cup)
Seaweed, dulse (3 1/2 ounces)
4 or 11
17
63 or 113
289
52
98
96
74
32
440
115
16
817
62
35
60
31
48
40
180
23
24
1700
Foods
Scallions, chopped (1/3 cup)
Soybeans,uncooked (1 ounce)
Spinach, cooked (1/2 cup)*
Squash, summer (3 1/2 ounces)
Swiss chard, raw (3 1/2 ounces)
Turnip greens, raw (1/2 cup)
Tomato, raw (one medium)*
Fruit:
Avocado (1 small)
Kiwi (1 1/4)
Pumpkin (1/2 cup)
Strawberries (1 cup)*
Nuts:
Mixed nuts (3 1/2 ounces)
Pistachios (3 1/2 ounces)
Meat and Fish:
Abalone (3 1/2 ounces)
Tuna canned in oil (3 1/2 ounces)
Beef liver (3 1/2 ounces)
Chicken liver (3 1/2 ounces)
Other:
Egg (1 large)*
Milk (8 ounces)
Soybean oil (1 Tablespoon)
Vitamin K in mcg
104
53
131 or 360
80
830
182
3 or 28
14
25
16
2.3 or 21
13
70
23
24
104
80
0.15 or 25
10
76