Health Services

Warfarin Management

Pregnancy & Warfarin

Warfarin is a safe drug when administered and monitored properly. Indeed, oral anticoagulation is a vital treatment for certain conditions, such as those listed on the Indications page of his symposium. However, one of the drawbacks for Warfarin is the potential for birth defects and/or hemorrhage in the offspring of mothers taking the drug.

There is apparently a link between some birth defects and Warfarin taken by the mother during early pregnancy. The actual degree (or percentage) of risk to the unborn child is not known. In most circumstances, Warfarin should be avoided in women of childbearing age unless there is no other option. If possible, another anticoagulant regimen should be used.

However, there are situations in women of child-bearing age where Warfarin is still the mainstay of therapy, such as recurrent pulmonary emboli. If a young woman needs to start Warfarin during the child-bearing years, it is very important to educate the patient on the potential harm to the unborn child and establish an effective birth control plan.

Before starting therapy, female patients should be asked about their intent to bear children in the future, their birth control methods at present, and their religious beliefs. For the woman who is not planning or desiring further children, sterilization by tubal ligation or hysterectomy would be the most reliable preventative step.

In younger women anticipating a new or enlarging family, Warfarin should not be prescribed if any other possible choice can be used. For some patients, this might mean daily shots with heparin, another anticoagulant medication which cannot be given by mouth.

If Warfarin is still required for clinical reasons, then birth control intervention must be prescribed as well. A longer acting form of birth control should be used (consult your GYN provider), since daily birth control pills could be accidentally or purposefully discontinued, risking an unwanted or unexpected pregnancy while taking Warfarin.

Educational services like Planned Parenthood can assist in selecting birth control methods that are acceptable to the patient and their lifestyle and/or values. Prevention is far better than dealing with the consequences after a pregnancy has occurred.

Occasionally a woman is diagnosed with heart or vascular problems during pregnancy. The most common form of heart problem discovered during pregnancy is mitral stenosis (from prior rheumatic fever). Some of these mothers will not survive delivery if the heart disease is left untreated. Intervention may require heart valve surgery even during the later half of the pregnancy.

Fortunately, the fetus tolerates heart surgery remarkably well and spontaneous loss of the pregnancy is rare. If possible, a tissue heart valve design should be used in this setting. Nearly all of these valves can be used without the need for Warfarin. However, if anticoagulation is required during pregnancy for any reason, it is best to administer heparin instead of Warfarin. Heparin cannot be given by mouth, and must be administered by shots under the skin three times per day, or by continuous intravenous infusion. Some pregnant mothers with heart problems or clotting problems will be placed on heparin shots for many months before the birth of their child. Fortunately, there is no known association between heparin and birth defects.

Dietary Considerations in Warfarin Patients

Warfarin acts by impairing the utilization of Vitamin K. The liver requires Vitamin K for the manufacturing of certain key proteins in the native clotting mechanism. When Vitamin K is not made available, these clotting factors are not manufactured, and blood clotting is impaired. At the same time, oral intake of Vitamin K will thus counteract the medicinal purpose of Warfarin, essentially acting as the antidote for Warfarin.

Sudden intake of large amounts of Vitamin K can diminish the effect of Warfarin, permitting the blood to clot. Some physicians place Warfarin patients on strict Low-Vitamin-K diets. Foods that are high in Vitamin K are discouraged. However, dietary restrictions rarely succeed over a long period of time.

Most patients return to eating their favorite foods, gradually at first. Thus the more prudent approach for Warfarin maintenance is to adjust the medication, not the diet. That is one of the very reasons for repeating the Pro-Time until a steady dose is found that provides the right anticoagulation regardless of the dietary intake of the patient. For your information, the following lists presents foods known to be high in Vitamin K.

  • Kale
  • Spinach
  • Broccoli
  • Turnip greens
  • Cauliflower
  • Chick peas
  • Brussels sprouts
  • Green tea
  • Beef, pork, or chicken livers
  • Soybean oil
  • Soy protein products (including tofu)
  • Vitamins A & E (large doses)

If your regular diet already contains these food items, Don't Change Your Eating Habits. Consistency in your daily eating pattern is the key. If you move to a new climate, or change your eating habits for any other reason, a new series of Pro-Times will be needed to make certain that your Warfarin requirement has not changed. However, even if it has changed, the best option is to change the dose which you take.

The information provided in this educational forum is solely for your information, and is not intended to replace actual recommendations or advice given by your treating physician.

Your Diet & Vitamin K

Warfarin works to keep your blood from clotting by decreasing the availability of Vitamin K. Vitamin K helps your blood to clot. These are opposing actions. Excessive Vitamin K intake can interfere with the Warfarin and allow your blood to remain susceptible to clots. Likewise, if you eat too little Vitamin K, the excess medication may cause your blood to become too thin. Your medication will be adjusted to the amount of Vitamin K typically in your diet. If you suddenly increase or decrease the amount of Vitamin K in your diet, your medication will not work properly.

A healthy, low fat diet following the Food Guide Pyramid is the best diet to follow. It is important for you to keep the Vitamin K content of your diet consistent. The amount of Vitamin K you eat affects the amount of Warfarin you require. Be sure to tell your healthcare provider if you change your diet. The medication will need to be adjusted to the amount of Vitamin K in your diet.

Some foods that are high in Vitamin K (i.e., leafy, green vegetables, broccoli, and cauliflower) can contribute to a healthy diet. Your efforts should be focused on keeping your intake of Vitamin K consistent from day to day. The first step is to evaluate your typical intake of Vitamin K foods by reviewing the food list in this packet.

Although there is little information about the effects of cooking, freezing, or drying on the Vitamin K content of foods, it appears that the Vitamin K content of cooked, frozen, or dried foods is about the same as fresh foods.

Evaluate your typical Vitamin K intake by reviewing the food list provided. The list contains foods that are known to be high in Vitamin K, as well as a few others that are not very high, but are often asked about by Warfarin patients. If you do not see a particular food on the list, it most likely contains very little Vitamin K, however, be sure to ask you dietitian about the food if you are concerned.

First, review the list to find foods that you are presently eating. Each list is identical. The first organizes foods from the highest Vitamin K content to lowest, while the second is in alphabetical order. Observe the amount of Vitamin K contained in the foods you eat. If you typically eat a larger portion than what is listed, be sure to increase the Vitamin K value proportionally. (i.e., there is 40ug of Vitamin K in ½ cup of lettuce, but you eat 2 cups worth in your salad, so you would actually have 160ug of Vitamin K in total). Add up the total amount of vitamin K that you typically consume in a day. Whatever it may be, 100, 200, 300, 400ug, etc., your job is to keep this daily intake as consistent as possible. By selecting combinations of foods, and/or adjusting portion sizes you should be able to consume about the same amount of Vitamin K each day.

If you should ever decide to dramatically change your typical daily intake of Vitamin K, be sure to inform your Doctor or pharmacist BEFORE making the change. They will most likely need to adjust your Warfarin dosage.

CAUTION - The following should be taken only with your physician's approval, because they also thin your blood, thus increasing the effect of your medication: alcohol, garlic pills, fish oil capsules, Vitamin E. Vitamin K tablets can also interfere with your Warfarin medication. Be sure to get your physician's approval, if you take Vitamin K tablets or a multi-vitamin pill with Vitamin K included. If you should have any additional questions or concerns regarding your daily intake of Vitamin K, please contact a dietitian at phone number (210) 292-7587 or 7472.

Highest to Lowest Vitamin K Content (Listed by food item, portion size and Vitamin K content)

  • Seaweed (Nori), 2 sheets (shredded), 511
  • Turnip greens, ½ cup, 470
  • Collard greens, ½ cup, 440
  • Spinach, ½ cup, 360
  • Brussels sprouts, ½ cup, 289
  • Kale, ½ cup, 270
  • Swiss chard, ½ cup, 249
  • Green tea, 1 oz (leaves)**, 199
  • Parsley, ½ cup, 162
  • Green scallion, ½ cup, 155
  • Broccoli, ½ cup, 113
  • Cauliflower, ½ cup, 96
  • Cabbage, ½ cup, 80-100
  • Liver (beef, pork, chicken), 3.5 oz, 80-100
  • Soybean oil, 1 Tbsp, 76
  • Endive, ½ cup, 69
  • Avocado, ½ cup, 57
  • Coriander, ½ cup, 52
  • Asparagus, ½ cup, 51
  • Mustard greens, ½ cup, 51
  • Green tomato, ½ cup, 50
  • Watercress, ½ cup, 42
  • Artichoke, ½ cup, 42
  • Lettuce, ½ cup, 40
  • Okra, ½ cup, 40
  • Soybeans, ½ cup, 34
  • Green beans, ½ cup, 33
  • Nettle leaves, ½ cup, 31
  • Red tomato, ½ cup, 25
  • Garbanzo beans, ½ cup, 22
  • Green peas, ½ cup, 22
  • Alfalfa sprouts, ½ cup, 16
  • Celery, ½ cup, 16
  • Cucumber (sliced with peel), ½ cup, 6
  • Green pepper, ½ cup, 5
  • Tofu, ½ cup, 2.5
  • Lima beans, ½ cup, 2

Vitamin K Content by Food Item (Listed by food item, portion size and Vitamin K content)

  • Alfalfa sprouts, ½ cup, 16
  • Artichoke, ½ cup, 42
  • Asparagus, ½ cup, 51
  • Avocado, ½ cup, 57
  • Broccoli, ½ cup, 113
  • Brussels sprouts, ½ cup, 289
  • Cabbage, ½ cup, 80-100
  • Cauliflower, ½ cup, 96
  • Celery, ½ cup, 16
  • Collard greens, ½ cup, 440
  • Coriander, ½ cup, 52
  • Cucumber (sliced with peel), ½ cup, 6
  • Endive, ½ cup, 69
  • Garbanzo beans, ½ cup, 22
  • Green beans, ½ cup, 33
  • Green peas, ½ cup, 22
  • Green pepper, ½ cup, 5
  • Green scallion, ½ cup, 155
  • Green tea, 1 oz (leaves)**, 199
  • Green tomato, ½ cup, 50
  • Kale, ½ cup, 270
  • Lettuce, ½ cup, 40
  • Lima beans, ½ cup, 2
  • Liver (beef, pork, chicken), 3.5 oz, 80-100
  • Mustard greens, ½ cup, 51
  • Nettle leaves, ½ cup, 31
  • Okra, ½ cup, 40
  • Parsley, ½ cup, 162
  • Red tomato, ½ cup, 25
  • Seaweed (Nori), 2 sheets (shredded), 511
  • Soybean oil, 1 Tbsp, 76
  • Soybeans, ½ cup, 34
  • Spinach, ½ cup, 360
  • Swiss chard, ½ cup, 249
  • Tofu, ½ cup, 2.5
  • Turnip greens, ½ cup, 470
  • Watercress, ½ cup, 42
  • Ensure, 8-oz can, 18

**Current analytical findings indicate that the brew from green tea leaves has negligible Vitamin K content.

Conditions Treated with Warfarin

Medical Conditions Commonly Treated with Warfarin Anticoagulation

Blood is meant to flow continuously, bringing vital nutrients and oxygen to every cell of the body. Blood should clot only when there is some injury to the blood vessel wall. This is a natural mechanism which prevents potentially fatal bleeding. If blood did not clot when a blood vessel was injured, even minor injuries could cause a person to lose a large amount of blood. Thus nature's defense is the natural clotting action of the blood. As anyone can observe from their own injuries, blood will clot within minutes if the proper conditions are present. In some disease states, clotting occurs when it shouldn't.

Blood clots which form in an abnormal time or location can be dangerous. These clots can break loose from their attachment and migrate into other body organs, causing damage. Large clots can obstruct blood flow.

To treat patients with clotting disorders, anti-clotting (or more appropriately "anticoagulant") medications are prescribed. Many of the indications for prescribing Warfarin are common health problems. A discussion of the most common reasons for prescribing Warfarin is presented below. However, not every patient with the medical conditions listed below will need (or can tolerate) Warfarin. If you have questions about your Warfarin prescription, or the reasons for administering the medication, consult your physician directly.

Conditions Commonly Treated with Warfarin Anticoagulation

  • Treatment of Deep Venous Thrombosis (DVT): a condition where clots form in the deep veins of the legs or pelvis.
  • Pulmonary Embolism (PE): a condition where the arteries bringing blood to the lungs fill with clots (which usually have migrated there from another site, such as the leg or pelvic veins).
  • Mechanical Heart Valves: prevention of clot formation on a new heart valve.
  • Mural Thrombus: a condition where clots form on the inside lining of the heart under the zone of a recent heart attack.
  • Stroke prevention: some causes of stroke can be treated with anticoagulant medications, including Warfarin.
  • Hypercoagulable State: a variety of medical and surgical conditions are associated with aggressive and harmful clotting, and responds to anticoagulant medications.
  • Chronic Atrial Fibrillation: an abnormal heart rhythm associated with clot formation in the upper chambers of the heart.
  • Congestive Heart Failure: some patients with very weak hearts will develop clots on the inside of the heart chambers and should take blood thinners to prevent further clot buildup and stroke.
  • Rheumatic Mitral Valve Disease: destruction of the mitral valve from rheumatic fever can lead to enlargement of the upper heart chamber, followed by formation of clots in the upper chamber.
  • Arterial Thrombosis: some patients with very poor circulation to the lower extremities (i.e. blocked arteries) have a tendency to suddenly form clot in the arteries.
  • Arterial Graft Thrombosis: after restoring the circulation to a lower extremity with a new (synthetic) bypass graft, clots can sometimes form in the graft. Anticoagulants often help reduce the chance of sudden graft closure.

Warfarin Interactions with Other Drugs

Drugs Which Interfere with Coumadin® Regulation Increased Warfarin Effect

Highly Probable

  • Alcohol (if concomitant liver disease)
  • Amiodarone
  • Cimetadine
  • Clofibrate
  • Cotrimoxazole
  • Erythromycin
  • Fluconazole
  • Isoniazid
  • Metronidazole
  • Miconazole
  • Omeprazole
  • Phenylbutazone
  • Piroxicam
  • Propafenone
  • Propanolo
  • Sulfinpyrazone Probable
  • Acetaminophen (Tylenol®)
  • Anabolic steroids
  • Aspirin
  • Chloral Hydrate
  • Ciprofloxacin
  • Dextropropoxyphen
  • Disulriam
  • Quinidine
  • Phenytoin (Dilantin®)
  • Simvastatin
  • Tamoxifen
  • Tetracycline
  • Influenza vaccine Possible
  • Disopyramide
  • 5-Fluorouracil
  • Ifosphamide
  • Lovastatin
  • Metolazone
  • Nalidixic Acid
  • Norfloxacin
  • Ofloxacin
  • Cefamandole
  • Cefazolin
  • Gemfibrozil
  • Heparin
  • Indomethacin
  • Sulfisoxazole

Decreased Warfarin Effect Highly Probable

  • Barbiturates
  • Carbamazepine
  • Chlorodiazepoxide
  • Cholestyramine
  • Griseofulvin
  • Nafcillin
  • Rifampin
  • Sucralfate Probable
  • Dicloxacillin Possible
  • Azathioprine
  • Cyclosporine
  • Etrelinate
  • Trazodone

No Warfarin Effect Highly Probable

  • Antacids
  • Atenolol
  • Bumetanide
  • Diflunisal
  • Enoxacin
  • Famotidine
  • Felodipine
  • Fluoxetine
  • Ketorolac
  • Metoprolol
  • Moricizine
  • Naproxen
  • Nitrazepam
  • Nizatidine
  • Psyllium
  • Ranitidine probable
  • Ibuprofen
  • Ketoconazole
  • Ketoprofen doubtful
  • Diltiazem
  • Tobacco
  • Vancomycin

Mechanisms of Warfarin Actions

Warfarin is an anticoagulant drug. It is only available by prescription, and should only be taken under the supervision of a physician familiar with its indications and actions. Warfarin is based on a chemical known as warfarin sodium. Warfarin causes its anti-clotting effect by impairing the production of certain blood clotting proteins by the liver.

Administration of warfarin sodium blocks the action of Vitamin K within the liver. The drug effectively competes for the same absorption sites within the liver needed for Vitamin K uptake. Thus, the levels of Vitamin K within the liver decrease. Reduced amounts of clotting factors VII, IX, X, and II are produced, and the clotting action of the blood is progressively impaired. All of the actions of Warfarin are due to the drug's inhibition of Vitamin K. Thus, ingestion or administration of Vitamin K can reverse the effects of Warfarin. In fact, clinical overdosage with Warfarin is corrected with Vitamin K.

Dietary intake of Vitamin K does affect the metabolism of Warfarin. This is one of the reasons that each patient seems to require a different dose of the drug to reach the target anticoagulation effect. Each person has different dietary intake of Vitamin K, and also different liver function, different excretion of the drug, etc. Thus it is important for the physician to monitor Warfarin effect on the patients clotting mechanism. Without a monitor, patients would frequently be overdosed or underdoses, with potentially hazardous consequences.

Monitoring of the Warfarin effect is performed with a blood test. This test is known as the INR or International Normalization Ratio. It is important that you review the INR information in The Anticoagulation Clinic and become familiar with the routine used to monitor this drugs effect.

Warfarin Precautions

Don't Mix Other Medications with Warfarin

The chief precaution with this drug revolves around interactions with other drugs. Some medications magnify the Warfarin effect, and some act as a relative antidote. Many common over-the-counter medications or remedies interfere with Warfarin regulation. Be advised that starting or stopping any medication could potentially affect your Warfarin control.

It is important to recheck your I.N.R. whenever starting or stopping any other medication. Aspirin is the most common drug which affects Warfarin regulation. Alcohol, antacids, antihistamines, antibiotics, and many other common medications also affect Warfarin. A list of medications which are known to interfere with Warfarin is included in this web site.

Follow a Schedule

Take your pill at the same time every day. It is easier to adjust your dose if you take your medicine in the evening. Although Warfarin can be taken any time in the day, it is prudent to take your dose at the same time each evening. If the doctor calls to adjust your dose, it is not much help if you have already taken your pills for the day. Thus the evening dosage schedule allows for easier adjustment. Many patients use a metered pillbox (one slot for each day of the week) and place it next to their toothbrush, for a convenient reminder.

Check Your Pills

It is possible for Warfarin pills to become mixed up. Even pharmacists have occasionally made errors, giving out the wrong tablet strength. Some patients who have had more than one strength of tablet in the household have mixed them up, with a resulting change in therapeutic dose. Keep close track of the color and insignia (indicating milligram strength) on each tablet, and at the time each prescription is filled.

Plan Ahead

If you are planning to travel outside of the country, refill your prescription. Make sure you have enough tablets for the entire trip, plus extras. Obtain your Pro-Time / I.N.R. before leaving to make sure that your dosage is proper. If you will be out of the area for an extended period of time, ensure that you obtain a "Travel Memorandum" from your provider. A Travel Memorandum allows you to travel and have your blood tested at other facilities that will fax the results back to your physician for them to properly dose and call you with any changes.

Inform Others

Let your family know you are taking anticoagulants. Make sure all your treating physicians know, especially new consultants who you have never seen before. Wear a Medic-Alert band or I.D. bracelet which informs others that you are taking Warfarin. Make sure your dentist is aware as well.

Dental Check-Ups

First, let your dentist know that you are taking Warfarin. Have regular check-ups to prevent and treat gum disease that might predispose you to bleeding during brushing or flossing.

Special Precautions

Avoid traumatic sports, if possible. Wear protective gear for activities like bicycle or horseback riding. Use a soft toothbrush to prevent gum injury. Use an electric razor rather than a straight or blade razor. Wear gloves while gardening.

Blood Testing

Dosing of Warfarin is individualized to each patient. There are different ranges of target values in different situations. It is important to know what target range your physician is using to treat your condition. Continue to have your blood draws as directed by your physician and / or nurse. After each blood draw, keep in touch with your physician's clinic to find out the results and what new dosage may be needed.


Warfarin is contraindicated in pregnancy. If pregnancy is a consideration, please consult your physician as soon as possible, preferably before conception.

What to Look For

The following symptoms could be a sign of excessive Warfarin dosage. If any of these symptoms occur, consult your clinic or physician.

  • Nose bleeds
  • Bleeding gums
  • Red or brown urine
  • Red or black stools
  • Cuts that do not stop bleeding
  • Bruises that enlarge
  • Excessive menstrual flow
  • Headaches
  • Abdominal pain
  • Faintness, dizziness, or unusual weakness

Warfarin Tablets

Warfarin (Coumadin®) Tablets - Color & Numerical Value (i.e., Label)

Each tablet is imprinted with a bold-faced numeral, indicating the milligrams of warfarin base in each tablet. There is a dividing line (or "score") across the middle of the front face of each pill. This permits the patient to easily cut the pill into two equal halves with a dull kitchen knife. Notice the similar colors between the 1 (one) milligram (pink) and the 5 (five) milligram (orange) tablet.

You cannot identify the different pills by color alone. Whenever you receive your prescription from the pharmacist, look at the identifying marks on the tablets and confirm the actual dosage with what your doctor prescribed. If the pills do not match, don't ingest any of them. Return them to the pharmacy right away and fill the proper dosage. Ingestion of pills that are too strong can result in serious, potentially harmful, bleeding complications.

Most patients are advised to take their Warfarin pills in the evening time. The action of Warfarin does not depend on the time of day. However, evening dosing of this drug makes it easier to adjust the amount after obtaining the results of the morning blood test. If the Pro-Time or INR indicate that an adjustment is needed, it is best if you have not already taken the dose for that day. For example, if you have your Pro-Time drawn in the morning, but also take your pill in the morning, your doctor would have more difficulty reducing your dosage if you have already taken the medication.

So, evening dosing is preferred in order to make dosing changes quicker and easier. Most patients purchase a 7-day (Monday through Sunday) pillbox. Each Monday, all seven days’ worth of Warfarin is placed into the slots. The pillbox should stay in the bathroom near your toothbrush. The easier way to take Warfarin is at the same time that you brush your teeth at night.

If you have small children in the household, the pillbox must be secured against accidental ingestion by a child. Should this occur, contact the nearest emergency room or poison control center right away. If recognized quickly, the effect of Warfarin can be reversed by administration of Vitamin K. Treatment for Warfarin ingestion would require hospitalization.

Using Warfarin Safely


It is important that you maintain the dosage prescribed for your Warfarin therapy. When you take your Warfarin, check to make sure you are taking the right tablets in terms of:

  • Milligram Dosage
  • Color
  • Number of Tablets
  • Generic Brand vs Warfarin Brand Name

You must take your Warfarin tablets on an unchanging schedule. You should take them:

  • at the same time every day
  • only in the prescribed amount

If you forget to take a tablet, let your physician know. DO NOT take another tablet to "catch up." Your prescription for Warfarin should be refilled only as directed by your physician. Other medications may affect the action of Warfarin.

  • Check with your physician before starting, stopping or changing the dose of any other medications. (This includes over-the-counter or topical drugs.)
  • Inform your physician if you have any illness that may require any other medications.
  • Inform other physicians or dentists that you are taking Warfarin.

You may wish to carry a card that identifies you as a patient on Warfarin.

Women: Warfarin should not be taken while you are PREGNANT. Inform your physician immediately if you are pregnant or if you are planning to become pregnant.


Because may factors can affect the action of Warfarin, it is important that you maintain a consistent lifestyle in terms of:

  • Eating habits (especially in regard to the amount of green vegetables you eat)
  • Exercise or physical activity
  • In general, you should report lifestyle changes to your physician

Avoid excessive use of alcohol. If you wish to change the amount of alcohol you normally drink, tell your physician.

Please check with your physician before starting on any extended trip as this may influence your medication availability, scheduled Protime/I.N.R. test, and eating habits.

Special Considerations

Because Warfarin therapy affects the clotting factors in our blood, it is important that you call your physician if any of the following occurs:

  • Bleeding - Prolonged bleeding from cuts, increased menstrual flow or vaginal bleeding, nosebleeds or bleeding from the gums. This includes unusual bruising, red or dark brown urine, and red or tarry black stools.
  • Diarrhea
  • Infection or Fever
  • Pain or Swelling

An Important Reminder

Please report all Protime/I.N.R. tests at scheduled times. This blood test is important. We will use this test to monitor the therapeutic effect of Warfarin in your blood and make adjustments to your dosage as needed.

If you have any questions about your Warfarin therapy, please ask your physician or clinic personnel.

Don't forget to keep your family's information up-to-date in DEERS.