WarfarinWarfarin Sodium

About Warfarin

Warfarin blocks the making of vitamin K-dependent clotting factors. The label covers preventing and treating clots in the veins and lungs; preventing and treating clots linked to atrial fibrillation or heart valve replacement; and lowering the risk of death, another heart attack, and stroke or other clots after a heart attack. It has no direct effect on a clot that has already formed. The dose is set for each person by the INR blood test, usually aiming for 2 to 3, and higher for some mechanical valves. Without genetic test results the usual starting dose is 2 to 5 mg once a day, lower in older or frail adults and in Asian patients; CYP2C9 and VKORC1 gene results, when known, help choose it, and loading doses are not recommended. The INR is checked daily after the first dose until it is stable in range, then generally every 1 to 4 weeks. When rapid anticoagulation is needed, heparin is given and overlapped with warfarin for 4 to 5 days and until the INR is in range. The label says the right dose, safety and effectiveness in children are unknown.

The boxed warning: warfarin can cause major or fatal bleeding, the INR must be checked regularly, medicines, diet changes and other factors move the INR, and patients should learn how to lower their bleeding risk and report signs of bleeding. It must not be taken in pregnancy (except by women with mechanical heart valves at high risk of clots), with bleeding tendencies or blood disorders, around recent or planned brain, spinal cord or eye surgery, with a spinal puncture or major regional anesthesia, with malignant high blood pressure, eclampsia or preeclampsia, by people who cannot be supervised and may not take it reliably, or after an allergy to it. Other warnings include death of skin and other tissue, usually within days of starting; calciphylaxis; acute kidney injury; cholesterol emboli; and limb ischemia or gangrene when it is used as the first treatment for heparin-induced thrombocytopenia. Bleeding from any tissue or organ is the most common side effect.

Drugs that block the liver enzymes CYP2C9, 1A2 or 3A4, such as amiodarone and fluconazole, can raise the INR, and inducers such as rifampin can lower it, so it is checked more often when an antibiotic, antifungal or herbal product is started or stopped. The label asks for a steady intake of vitamin K, avoiding activities that could cause injury, and carrying identification that says warfarin is taken. It can harm a developing baby, so pregnancy is ruled out first and effective contraception is used during treatment and for at least a month after; breastfed infants are watched for bruising or bleeding. Tablets are scored and colored by strength, as labeled: 1 mg pink, 2 mg lavender, 2.5 mg green, 3 mg tan, 4 mg blue, 5 mg peach, 6 mg teal, 7.5 mg yellow and 10 mg white (dye-free).

Taking Warfarin

How to take it

Once a day at about the same time, with or without food, at the dose your INR results call for; keep every INR test appointment. Keep your vitamin K intake steady from week to week, and avoid sudden large changes, such as eating much more leafy green vegetables.

If you miss a dose

Take it as soon as you remember if it is still the same day. Do not double the next day’s dose to make up for a missed one, and tell the prescriber about any missed dose.

Storage

At room temperature, 68°F to 77°F (20°C to 25°C), protected from light and moisture, in a tightly closed container, out of reach of children. Do not flush it; use a medicine take-back program.

Interactions to know about

Amiodarone and fluconazole can raise the INR, rifampin and carbamazepine can lower it, and antibiotics and antifungals can change it. Aspirin, clopidogrel, other anticoagulants, NSAIDs and SSRI or SNRI antidepressants raise bleeding risk; garlic and ginkgo may add to it, and St. John’s wort and ginseng may weaken warfarin.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Warfarin differs from pharmacy to pharmacy

Generic warfarin comes from several makers, and quotes for the same tablet can differ between pharmacies. Doses change with INR results, so fills can be frequent and of different sizes, and a weekly schedule that uses two strengths means two separate fills.

Ways to pay less for Warfarin without insurance

• Ask whether warfarin is on the pharmacy’s flat-price generic list, and compare more than one pharmacy.
• Once your dose has been stable for a while, ask for a ninety-day supply of each strength you use.
• If your schedule uses two strengths, ask the prescriber whether a single strength could cover it, so there is one fill instead of two.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Warfarin

1. 1.Do any of my other medicines, antibiotics or supplements change my INR?
2. 2.Is this the same strength and tablet color as my last fill?
3. 3.What should I do if I miss a dose or take an extra one?
4. 4.Which bleeding signs mean I should get help right away?

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