Warfarin Patient Tips

How it works

Warfarin blocks the formation of vitamin K-dependent clotting factors, thereby decreasing the body's ability to form blood clots - often described as "thinning the blood".

Upsides

• Decreases the body's ability to form blood clots and is used in the prevention and treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE). Also used to prevent blood clots from developing as a result of atrial fibrillation or cardiac valve replacement.
• Used to decrease the risk of death after a heart attack (myocardial infarction) or stroke due to a blood clot.

Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

• Major and fatal bleeding.
• Warfarin has a narrow therapeutic range - meaning that there is a fine line between too much and too little. For this reason, regular blood monitoring of the international normalized ratio (INR) - a standardized number that determines the ability of your blood to clot - is required. Frequency of monitoring varies; daily monitoring is required initially. Ongoing monitoring frequency depends on patient response, but may need increasing for numerous reasons such as during times of illness or with dietary or medication changes.
• Warfarin cannot break apart established blood clots, nor can it reverse damage to tissue that has already been starved of oxygen. It can; however, prevent the extension of existing blood clots and reduce the risk of part of that blood clot breaking off and lodging in another artery or vein.
• Should not be used by women who are pregnant or planning to become pregnant, except under specialist advice, as warfarin can harm a developing baby.
• Warfarin interacts with numerous drugs including certain types of antibiotic, heart medications, oral contraceptives, pain medications and acid suppressants. Warfarin also interacts with several types of botanicals, including co-enzyme Q10, St. John’s wort, ginseng, echinacea, ginkgo, golden-seal; as well as grapefruit juice. See here for a full list of interactions.

Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.

Bottom Line

Warfarin tablets are effective at "thinning" the blood; however, a number of factors affect blood levels including diet, race, other medications, and illness. Too much warfarin can cause major and potentially fatal bleeding.

Tips

• Be aware that foods containing vitamin K can affect warfarin therapy. Try to eat a normal, balanced diet, to maintain a consistent intake of vitamin K - avoid eating too much of one thing (for example, a whole plate of broccoli, or a big bowl of salad greens). Foods high in vitamin K include kale, collards, broccoli, spinach and other green leafy vegetables. Cranberry juice and alcohol may also affect warfarin levels so limit intake of these.
• No one dosage fits all. The dosage schedule for warfarin needs to be tailored for each individual depending on their own INR response to the drug and the condition being treated. Patient factors such as age, weight, race (Asian patients may need lower dosages), body weight, sex, concomitant medications, and comorbidities all affect dosage as do some genetic factors (for example, CYP2C9 and VKORC1 genotypes).
• An initial lower starting dose is recommended in seniors or the frail and in people of Asian descent.
• Loading doses ( a bigger dose at the start) are no longer routinely recommended as these increase the risk of bleeding without offering any more rapid protection against clot formation.
• If you miss a dose, and it is the same day, you may take that dose. However, if you do not discover the missed dose until the next day, do not double up on the dose (just forgo the missed dose).
• You may need to temporarily stop or change your warfarin dosing schedule if you have planned surgery (including eye surgery) or a dental procedure. Discuss this with your surgeon or dentist prior to the procedure.
• Monitor yourself for signs of bleeding such as blood in your stools or urine, nose-bleeds, bleeding gums, excessive menstrual bleeding or excessive bruising and seek immediate medical advice. Also take care to minimize your risk of bleeding - avoid full-contact sports, be careful with knives and try to minimize your risk of falling.
• Always adhere to your prescribed dosage schedule. Ask your doctor before you take or discontinue ANY other drug, including over-the-counter medicines and botanical (herbal) products. Ensure you get your blood levels monitored as instructed.
• Wear or carry identification that states you are taking warfarin tablets, in case of an emergency.
• Although Coumadin and Jantoven are both brands of warfarin, small changes in their formulation may mean your body reacts differently to each brand. Most experts recommend you stick with the same brand of warfarin to help keep your INR levels stable.
• Contact your doctor if you develop severe diarrhea, an infection or a fever.

Response and Effectiveness

• Some slowing of the blood's ability to clot may be noticed within 24 hours; however, it can take from 72 to 96 hours for the full effects to be seen. One dose of warfarin lasts for 2 to 5 days. Effects are likely to accumulate with repeated dosing because of the time it takes for the affected vitamin K-dependent clotting factors to replenish.
• Desired INR range varies depending on condition and specific guidelines; however, the majority of guidelines aim for a target INR of 2.5 (range 2-3).
• Treatment duration also varies, from three months to life-long depending on the condition and other patient factors; generally until the danger of thrombosis or embolism has passed.
• INR readings greater than 4 are associated with a higher risk of bleeding with no additional therapeutic benefit in most people.