More ways to keep blood levels in a safe range with warfarin

4. Make sure all doctors know you take warfarin, and ask them to check for interactions when antibiotics or other new medications are prescribed.

Warfarin interacts with a truly mind-boggling array of commonly prescribed medications, including many antibiotics. Some strengthen warfarin's effect (thus increasing the risk of bleeding), whereas others weaken warfarin's effect (increasing the risk of blood clots and stroke).

What to do:

• Bring an up-to-date medication list to every doctor's visit or, better yet, bring all medication bottles.

• Whenever a new medication is prescribed, ask the doctor to check for a possible interaction with warfarin. Many doctors have access to computer programs that can check for interactions on demand.

• If you need to take a medication that will affect warfarin, make sure there's a plan to adjust your warfarin dose, or at least check on your INR more frequently.

• Get all prescriptions from the same pharmacy. Pharmacies are often able to check for drug interactions, which can be a helpful backup system.

5. Be extra-careful about regularly using aspirin, acetaminophen, or NSAIDs.

Although occasional use for a headache or sore joint should be fine, these common over-the-counter medications can all increase the risk of bleeding in people on warfarin. Regular use (daily for more than a week) of acetaminophen increases INR; this can be countered by lowering the weekly dose of warfarin. Aspirin and NSAIDs such as ibuprofen don't affect INR but do cause stomach irritation, which can predispose someone taking warfarin to bleeding.

What to do:

• Don't take aspirin, acetaminophen, or NSAIDs on a daily basis without discussing the bleeding risk with the doctor.

6. Avoid herbal remedies and supplements known to affect clotting.

Many herbal medications have been shown to at least theoretically affect certain clotting factors within the blood. Anyone on warfarin should probably avoid these. Otherwise their use should be discussed with the doctor so that extra blood monitoring can be arranged.

What to do:

• Be careful about supplements containing any of the following: alfalfa, angelica, aniseed, arnica, asafetida, celery, chamomile, clove, fenugreek, feverfew, fucus, garlic, ginger, ginkgo, ginseng, horse chestnut, horseradish, licorice, meadowsweet, poplar, prickly ash, quassia, red clover, willow.

• Note that dietary doses -- doses commonly used in cooking -- of garlic and ginger have not been shown to lead to increased bleeding events in people on warfarin.

7. Ask about self-monitoring at home.

Several handheld finger-stick devices now are FDA approved for checking INRs at home. Some people on warfarin do their own monitoring and adjustment, with the support of instructions and backup from a clinician's office. In 2010, a large study found that rates of bleeding on warfarin were the same whether people were monitored in a special warfarin clinic or they performed self-monitoring. However, the study also found that people reported more satisfaction and slightly better quality of life, on average, with home monitoring.

What to do:

• If you're the independent, do-it-yourself type, or if frequent visits to the doctor are a hardship, consider asking for a self-monitoring device. You'll need to be trained to use it, and your healthcare provider will need to provide clear instructions on how to adjust your warfarin.