Warfarin (Coumadin) Safety

There are 4 million people in the USA taking warfarin for Atrial Fibrillation and hundreds of thousands of patients taking warfarin due to prosthetic heart valves, history of DVT’s, pulmonary emboli, and coagulation disorders. The proper management of warfarin is critical for it to be effective, and safe.

The “INR” (International Normalized Ratio) is what doctors use to measure the degree of anticoagulation and use it to adjust the warfarin dosage. Following the below guidelines will decrease errors and improve the stability of the INR measurement.

Very slight changes in the warfarin dosage (such as missing one dose) can result in a big change in the INR (the amount of anticoagulation or thinning of the blood). Following the below guidelines will result in a more stable INR and reduce errors.

Warfarin Best Practice Guidelines

Pill Boxes: I require that ALL my patients on warfarin use pill boxes. This will not prevent a patient from missing a dosage, but will cause the patient to notice when he or she misses a dosage. Fill the pill box just once a week. We recommend that you have a special pill box with ONLY the warfarin in it.

Bring in the pill bottles and pill boxes: When you come in for an appointment, bring in your warfarin pill bottles and your pill boxes. Sometimes we may give an extra dosage “on the spot” or refill your pill box for you after making a change. I have also found patients with the WRONG size of tablet from the pharmacy.

Checking the INR and making changes: The INR must be checked at least once a month when it is stable. If you are just starting, or a change has been made, you will need to check your INR more often. We prefer that only one office make changes when possible, but sometimes it is necessary for another doctor to make a change. If this happens, please inform us ASAP to update our records.

Warfarin Strength: We prefer that each patient only have ONE pill size (strength) at home. We prefer that you show us all your pill bottles and dispose of unused pills if the strength has been changed.

When to Take Warfarin: We prefer that you take warfarin in the evening after 6 pm. However, this is only so that we can change your dosage, if necessary, before you have taken your dosage that day. Some patients take their warfarin in the morning if they cannot remember to take it.

The “Buddy System”: Some patients forget to take their warfarin. In these cases, we prefer to have a “buddy” help remind them. Missing just ONE DOSAGE can alter the INR results. Taking one extra dose can also result in altering the INR dramatically.

Medication Interaction: Always bring all your medication bottles to show a doctor and always tell them you are taking a blood thinner. Many medications interact with warfarin including antibiotics. Starting a new medication can also require increased testing of the INR. Consult your doctor about taking aspirin with warfarin. Avoid other NSAIDS or “arthritis medications”. Inform your doctor before taking over the counter medications.

Missed Dosage: If you miss a dose of warfarin, you should contact your doctor or take it as soon as you realize you missed it as long as more than 24 hours has not passed. This should NOT be done with most other medications. Wafarin has a very long half life so this is way you can still take it as long as 24 hours has not passed.

Warfarin, Diet, and Vitamin K: In the “old days” it was thought that fluctuations in the INR were due to eating foods with vitamin K and due to the diet. Now we know that MANY explanations exist for fluctuations in the INR. One of the most common is simply forgetting doses and miscommunications between the patient and the doctor. It turns out that patients taking warfarin can eat some vegetables. In fact, diets VERY low in vitamin K can result in unstable INR’s. However, if you are going to change your diet or add a vitamin that could contain vitamin K please consult with your doctor first as this may require increased testing and a dosage adjustment.

Warfarin and Illness: If you become ill, and are not eating well, your INR could become unstable. Please see your doctor if you become ill while taking warfarin.

Bleeding: If you experience black stools, bruising, or bleeding on warfarin, please inform your doctor or seek medical attention so he or she can check your INR and evaluate you.

Procedures and Surgery: If you are going to have a procedure or a surgery, please inform your doctor that you are taking warfarin. Not all procedures require you to stop warfarin, so be sure and consult with your doctor for instructions.

Wafarin Adjustment: When the INR is not in the desired range, an adjustment will normally be made to your schedule. Because very slight changes in the dosage will affect the INR, changes in the total weekly dosage are usually very small – usually 7% to 14% of the total weekly dosage. Therefore, it is important that you write down and understand the new schedule and don’t make any errors. If you are confused about your new warfarin dosage schedule, be sure and ask your doctor.

Before making any of the above changes, please consult with your doctor.