Patient discussions
Patient education is essential before starting warfarin. Patients should be informed about the proper use of warfarin, the need for a regular blood clotting test (international normalized ratio [INR]), and the need for regular follow-up.
Dosing and monitoring of warfarin differs from many other medicines.
Warfarin makes the blood more difficult to clot and, therefore, carries a risk of bleeding.
The effect of the drug is measured with the INR.
Warfarin dose frequently changes over time, and dosing that varies with the day of the week is very common (e.g., 4 mg on Monday, Wednesday, Friday, and Sunday; 5 mg on Tuesday, Thursday, and Saturday).
Dosing is typically referred to in weekly dosing amounts given the day-to-day fluctuations in dose.
The desired or target INR values are generally between 2 and 3.
The INR must be checked (monitored) frequently, with blood tests, often once or twice weekly until the stable dose is reached, then on an extended interval (4-12 weeks) thereafter.
Patients should be instructed on how to handle a missed dose (the approach may vary according to the warfarin manager).
Patients must be very clear about the daily dose of warfarin and the colors of their different warfarin tablets.
A pill organizer can help.
Many drugs interact with warfarin.
The physician/healthcare provider who oversees the warfarin treatment must be notified whenever a new medicine (e.g., prescription or over-the-counter medicine, supplement, or herbal therapy) is started for the first time, or when a current medication is stopped or the dose is adjusted. Nonsteroidal anti-inflammatory drugs (NSAIDs) should be avoided or used with extreme caution under physician supervision.
Even when medications do not interact with INR testing, they may still increase the risk of bleeding through pharmacodynamic interactions (NSAIDs, selective serotonin-reuptake inhibitors).
Diet changes can affect the INR.
Intake of foods with high amounts of vitamin K (e.g., spinach, broccoli) can particularly affect the INR; eating any amount of vegetables or food high in vitamin K is acceptable, so long as the intake is consistent from week to week.
Alcohol should be consumed with caution and only in small amounts.
Grapefruit juice should be avoided.
Avoid high-risk activities.
Activities that carry a high risk of trauma or serious bleeding should be avoided or, if this is not possible, additional safety precautions should be taken.
Direct oral anticoagulants (DOACs)
DOACs do not require coagulation assay laboratory monitoring. Several medications can interact with DOACs, leading to increased risk of bleeding or increased risk of thrombosis (e.g., primidone, amiodarone, diltiazem, verapamil, rifampin, phenytoin, phenobarbital). Interactions are most commonly mediated via cytochrome P450 enzyme (CYP450) and/or the transporter permeability glycoprotein (P-gp).[230]
Patients with subsegmental PE and no proximal DVT in the legs who have a low risk for recurrent VTE should be informed about clinical signs and symptoms of progressive thrombosis to watch for and the need for reassessment if these are present.[21]
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