A Patient On Warfarin With Increased INR

A 65-year-old with a history of chronic atrial fibrillation is being monitored while on warfarin therapy. The nurse calls to inform you the patient’s international normalized ratio (INR) is measured at 7. He has no active signs of bleeding, but is at increased risk of bleeding. Appropriate management at this time includes which of the following:

A) Stop warfarin, observe, and repeat INR in 3 days.
B) Stop warfarin and observe; repeat INR in 24 hours.
C) Stop warfarin, give vitamin K, and repeat INR in 24 hours.
D) Stop warfarin, give vitamin K and fresh-frozen plasma with daily INRs.

Answer:



C : Stop warfarin, give vitamin K, and repeat INR in 24 hours

Warfarin inhibits the formation of clotting factors II, VII, IX, and X. The drug is highly protein bound to albumin. Because of this inverse relationship between the levels of albumin and free warfarin, acutely ill patients with poor nutritional states and postoperative patients may need
lower dosages of warfarin. The INR is the patient’s prothrombin time divided by the mean of the normal prothrombin time, with this ratio raised to the international sensitivity index. After starting warfarin therapy, a steadystate response is not typically achieved for approximately 2 weeks. A
dosage of 4 to 5 mg per day is typical, although the required dosage may be variable (as low as 0.5 mg or as high as 50 mg per day). Elderly patients should start at a lower dosage.
Checking the INR approximately 24 hours after the first dose can help determine the second dose. If there has been little or no rise in the INR (which is to be expected), a 5-mg dose on the second day should be safe. If an INR is not available on the day after the first dose, it can be obtained on days 2, 3, or 4. If the initial INR (on days 1 through 4) is high, the patient is likely sensitive to warfarin’s effects; therefore, a lower dose should be given. Patients who are restarting warfarin therapy after a time off the drug can safely begin with their previous maintenance dose. Guidelines recommend that the INR be checked at least four times during the first week of therapy. This frequency could then be
gradually decreased on the basis of the stability of the INR. Because the risk of bleeding is greatest in the first 6 to 12 weeks of treatment, checking the INR weekly is appropriate. The maximum time between tests should be no more than 4 to 6 weeks. If a patient’s INR has been stable and then
fluctuates by more than 0.2 below or 0.4 above the goal INR, the patient should be evaluated for the cause of the change. Associated causes include laboratory error, noncompliance, drug interactions with warfarin, dietary interactions, or a change in the patient’s health. If no reversible cause is found, a change in dosage may be made, with a repeat INR within 2 weeks. Close follow-up with repeated testing is needed because the patients who have the most variation in results are most likely to develop bleeding or thromboembolism. In asymptomatic patients whose INR is elevated, temporary discontinuation of the drug is often used, but administration of vitamin K shortens the time to return to the target INR. There is indirect evidence that use of vitamin K is associated with a lower incidence of hemorrhage. Oral vitamin K is effective and may have fewer risks than the parenterally administered form. When a patient’s INR is between 5 and 9, the recommendations include temporary discontinuation of warfarin therapy.
If the patient is at risk for hemorrhage (e.g., is taking nonsteroidal antiinflammatory
drugs [NSAIDs]), low-dose oral vitamin K (1.0 to 2.5 mg) also should be given. However, the lowest dose available in tablet form is 5 mg, and often only 1 or 2 mg is needed. The parenteral form can be given orally and mixed in a flavored drink if needed. If the patient cannot be treated orally, 0.5 to 1 mg of intravenous vitamin K should be administered.
For INRs of 9 or higher, vitamin K also should be given at a higher dose
(2.5 mg intravenously or 5 mg orally).
A repeat INR should be obtained within 24 hours. Additional vitamin K may be needed, depending on the result of the repeat INR. If the INR is elevated and the patient is bleeding,fresh-frozen plasma or a concentrate of clotting factors should be administered. A repeat INR should be obtained shortly after the fresh-frozen plasma is given. Additional fresh-frozen plasma may be needed because of its short duration of action. A large dose of vitamin K (10 mg) should also be given. Additional vitamin K may be necessary because the half-life of warfarin is longer than the half-life of vitamin K. Daily INR measurements should be instituted. 50