Warfarin Patient Counseling Guide
A Quick Guide to Effective Patient Care
Most of the time when patients are first prescribed warfarin, they panic. Many patients think of warfarin as the “rat poison drug” and automatically assume it’s terrible for them. Some patients may prefer warfarin because its heavily monitored and some may prefer DOACs (direct oral anticoagulant) instead due to the convenience of less doctor/pharmacist visits and keeping track of their diet.
Warfarin is an anticoagulant that requires additional monitoring compared to a DOAC. This monitoring is usually performed by a healthcare professional and can be done frequently to monthly depending on the patient. My focus will be based on a pharmacist’s perspective.
What is Warfarin
Warfarin is a vitamin K antagonist that is used for stroke prevention in atrial fibrillation, DVT/PE treatment and prophylaxis, history of stroke, or cardiac valve replacements. Warfarin has a delayed onset of action and may take 1 to 3 days for desired response. Sometimes depending on the specific patient’s situation and the clinic’s guidelines, bridging with Lovenox may be an option to acquire the patient’s INR goal.
What is INR (International Normalized Ratio)
INR is a laboratory measurement of how quickly the patient’s blood coagulates. The common INR goal for patients is usually 2–3 but can be 2.5–3.5 in mechanical valve replacement, or at the cardiologist’s discretion. If the INR is above goal, meaning the warfarin dose is supratherapeutic, the blood is too thin and the patient is at an increased risk for bleeding. When the INR is below goal, meaning the warfarin dose is subtherapeutic, the blood is too thick and the patient is at risk for developing a clot and further complications. It is important that the INR is monitored in new patients, so that we can find a stable dose and customize that dose to their diet and lifestyle.
Counseling Tips
When patients start warfarin, teach them everything in layman’s terms, make sure they are aware of what INR is and what goal they should be aiming for. Inform them of the point of care machine that measures their INR. With the point of care machine, warn them that you will have to prick their finger with a lancet to get blood to put on the test strip and enter it into the machine.
For each appointment visit, quiz them and see if they are aware of the warfarin dosing schedule and make sure they are taking the correct dose and correct tablet. Some patients may have different strengths of warfarin at home. If they no longer need it, encourage them to dispose of the tablets to lessen confusion. Warfarin comes in various colors and each strength represents a different color. To prevent your patient from taking the wrong dosage, make sure they are mindful of exactly how they should take warfarin. Use the teach back method to confirm understanding.
In addition to the correct use of warfarin, a quick questionnaire should be performed. The questionnaire should contain if they had any issues with the medication, if they missed any doses or medication changes and if they need any more refills. Other questions, such as if they had any bruising or bleeding or recent falls or injuries, are also important to ask.
Warfarin has many drug and food interactions that also require monitoring. Consumption of alcohol is an example of a beverage that can increase INR. Counsel your patients to limit the consumption of alcohol or try to avoid it completely, if possible. If a patient consumes vitamin K, it can decrease their INR and decrease the effectiveness of warfarin. It is important to know what food your patient is eating so that it would make sense if an INR reading is abnormal. If the patient insists on consuming foods with vitamin K such as green leafy vegetables, they can still eat it as long as they’re consistent. In this case, warfarin would need to be adjusted to the patient’s specific diet to keep them in therapeutic range.
Many drugs interact with warfarin, it is important to ask your patient if they recently started taking any new drugs: OTC, prescription, vitamins, etc. Always check for drug-drug interactions and adjust or discontinue drugs accordingly. Some drugs that may interact with warfarin include amiodarone, sulfamethoxazole/trimethoprim, and azole antifungals, just to name a few; there are many more!
Conclusion
It is important to know how to counsel your patients on any medication. Warfarin is a medication that comes with a lot of monitoring parameters so to protect your patients, counsel them effectively and target a therapeutic INR.
Ramsey Reed, Pharm.D. Candidate
