INR > 4–5 or active bleeding — hold the dose and notify the provider
Before you read
Test yourself first: 5 questions
Question 1 of 5
A client is prescribed warfarin 5 mg daily. The nurse notes the client is also taking an antibiotic that displaces warfarin from protein-binding sites. What effect should the nurse anticipate?
Answer: A. Drugs that displace warfarin from protein-binding sites increase the amount of free, active warfarin, raising the INR and the risk of bleeding. The nurse should monitor for an elevated INR and bleeding. This interaction does not decrease warfarin effect or render it ineffective.
Question 2 of 5
A client on warfarin reports starting several new supplements. Which substance most increases the risk of bleeding by potentiating warfarin?
Answer: B. Vitamin E and many herbal supplements such as ginkgo, garlic, and ginger increase bleeding risk with warfarin. In contrast, foods and supplements high in vitamin K (like spinach or kale) reduce warfarin effect; consistency, not avoidance, is the teaching point.
Question 3 of 5
A client taking warfarin has an INR of 8.5 with no active bleeding. Which agent is used to reverse the effect of warfarin?
Answer: B. Vitamin K (phytonadione) is the antidote for warfarin, restoring synthesis of vitamin K-dependent clotting factors. Protamine reverses heparin, and the others are not warfarin reversal agents.
Question 4 of 5
A nurse reviews the medication list of a client newly prescribed warfarin. Which finding requires immediate follow-up with the provider?
Answer: B. A history of recent hemorrhagic stroke is a contraindication to warfarin because the drug greatly increases bleeding risk, including intracranial bleeding. Atrial fibrillation, a mechanical heart valve, and deep vein thrombosis are common indications for warfarin therapy, not contraindications.
Question 5 of 5
A nurse is teaching a client newly prescribed warfarin about dietary considerations. Which statement by the client indicates correct understanding?
Answer: B. Clients on warfarin should maintain a consistent intake of vitamin K-containing foods such as green leafy vegetables, because fluctuating intake alters INR control. The goal is consistency, not complete avoidance. Vitamin K antagonizes warfarin, so large sudden increases can lower the INR.
Keep the streak going with more questions like these, each with a full rationale.
What is warfarin therapy?
It takes several days to reach full effect, so heparin or enoxaparin is overlapped for at least 5 days and until the INR is in range. It is monitored with PT/INR, its antidote is vitamin K, and it is used for long-term clot prevention (atrial fibrillation, DVT, mechanical heart valves).
Key points to remember
- Monitor PT/INR — therapeutic INR is usually 2–3 (2.5–3.5 for mechanical valves)
- Antidote: vitamin K (phytonadione)
- Onset is slow, so heparin often 'bridges' until warfarin is therapeutic
- Many drug/food interactions — green leafy vegetables (vitamin K) reduce its effect
- Warfarin crosses the placenta and causes birth defects, so it is avoided in pregnancy; heparin is used instead.
- Many drugs change its effect — some antibiotics and amiodarone raise the INR, while rifampin and carbamazepine lower it — so every new drug is checked.
- Herbal products such as ginkgo, garlic and ginger add to bleeding risk; St. John's wort reduces warfarin's effect.
Nursing priorities
- Check INR regularly and assess for bleeding
- Keep vitamin K available as the reversal agent
- Teach a consistent (not necessarily low) vitamin K intake — avoid big swings
- Give it at the same time each day and check the INR result before the dose when ordered.
- Assess for bleeding: gums, urine, stool, bruising, nosebleeds and heavy menstrual bleeding.
Labs & values
Patient teaching
- Keep leafy-green intake steady; avoid alcohol; tell every provider you take warfarin
- Use a soft toothbrush and electric razor; report unusual bleeding
- Wear a medical alert ID and tell every provider and dentist that you take warfarin.
- Do not double a missed dose; call the provider for instructions.
- Do not start any new medicine, supplement or herbal product without asking first.
Red flags: report now
- INR > 4–5 or active bleeding — hold the dose and notify the provider
- A severe headache, sudden confusion or one-sided weakness may mean bleeding in the brain — treat as an emergency.
- Purple, painful toes or areas of skin necrosis are rare but serious reactions to report.
References
Clinical references for this topic
