What are the risks of taking warfarin?

What should I tell my doctor before starting warfarin?

You should not take warfarin if you are allergic to it. Signs and symptoms of an allergic reaction include difficulty breathing, hives (rash on your body), swelling of the face, lips, tongue, or throat.

Warfarin is not the safe choice for you if you cannot take warfarin on time every day.

To make sure warfarin is safe for you, tell your doctor if you have:

• Liver, kidney disease, or if you are on dialysis 
• Congestive heart failure
• Diabetes
• A clotting deficiency 
• Low blood platelet after receiving heparin

You should not take warfarin if you have:

• Very high blood pressure
• Recent surgery on the brain, spine, or eye, or you will have these types of surgery in a near future
• Undergo a spinal tap or epidural (spinal anesthesia)

Certain medical conditions increase the risk of bleeding. You should not take warfarin if you are prone to bleeding because of the following medical conditions:

• Blood disorders (low red blood cells or low platelets)
• Stomach bleeding or ulcers
• Brain aneurysm or bleeding in the brain
• Endocarditis (infection of the lining of the heart)
  • Keep all blood tests and doctor appointments, as INR monitoring is essential for warfarin dosing.
  • Keep in mind that small changes in daily living can affect INR.
  • Some simple changes to decrease the risk of bleeding:
    • Use a soft-bristle toothbrush. 
    • Use waxed floss rather than unwaxed floss.
    • Use an electric razor rather than a blade. 
    • Use extreme caution when using sharp objects, such as knives and scissors. 
    • Avoid activities that have a high risk of falling or injury (e.g., contact sports)
• Let your healthcare provider know if you have surgery, dental work, or other medical procedures; your healthcare provider will give you instructions on how to stop taking warfarin. 
• Tell your healthcare provider of all medications and supplements you are taking. Certain over-the-counter products are not to be used while taking warfarin. For example:
  • NSAIDs (nonsteroidal anti-inflammatory drugs) are not to be used while being on warfarin. NSAIDs (nonsteroidal anti-inflammatory drugs) can cause gastrointestinal bleeding, which can be more severe when taken with warfarin.
  • Selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) are two classes of antidepressants. Both selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) carry bleeding risk; therefore, taking warfarin with an SSRI or SNRI is not recommended due to the added risk of bleeding. 
• Vitamin K intake can affect the PT (prothrombin time), INR, and the effectiveness of warfarin. The critical thing to note here is that you should not entirely stop eating vitamin K-rich foods that you usually eat, nor should you suddenly add foods, beverages, or vitamin K-rich supplements to your daily diet. You should keep vitamin K intake as consistent as possible.
  • Sudden increases in vitamin K-rich food can decrease the INR and warfarin’s effectiveness. Blood clots can form as a result.
  • A sudden decrease in vitamin K intake can increase INR and warfarin’s effects, leading to an increased risk of bleeding or other severe bleeding problems. 
• To keep vitamin K levels consistent, you should not make too many dietary changes and be very careful with nutritional supplements or herbal products. You should report any changes in diet or medications to your healthcare provider immediately. 
• Examples of foods rich in vitamin K:
  • Green leafy vegetables such as spinach, kale, collard greens, mustard greens, green leaf lettuce, romaine lettuce, turnip greens, parsley, and endive
  • Broccoli, Brussel sprouts, asparagus, cabbage, peas
  • Avocado, prunes, blueberries, blackberries
  • Tuna, beef liver, or animal liver products
• Remember that vitamin K can also be found in certain nutrition supplements such as Boost, Ensure, and Slim Fast. Tobacco and tobacco products also contain vitamin K.

What drugs can interact with warfarin?

Many drugs, including prescription medications, over-the-counter products, and herbal medicines, can interact with warfarin. These drug interactions can affect your INR level and may increase your risk of bleeding. Before you start or stop using any medications, you need to let your doctor or pharmacist know of any changes, especially the following medications, medication classes, and supplements:

• Other oral anticoagulation therapy to prevent blood clots
• Antibiotic or antifungal medications 
• Any supplements that contain vitamin K
• Cranberry and cranberry juice 
• Herbal supplements: garlic, ginkgo, coenzyme Q10, echinacea, Biloba, goldenseal, and St. John’s wort

This is not a complete list. Other drugs, including prescriptions, over-the-counter products, herbal supplements, and vitamins, may interact with warfarin. Not all potential drug interactions are listed in this guide. It is highly recommended to keep a list of all the drug products you are using (prescriptions, over-the-counter products, herbal supplements, natural products, and vitamins) and share it with your doctor and pharmacist.