Consistent vitamin K keeps the INR stable
Warfarin is a vitamin K antagonist: it blocks the liver's recycling of vitamin K, which is needed to activate clotting factors II, VII, IX, and X. Because its effect depends on how much vitamin K is available, sudden changes in the intake of vitamin K-rich foods such as green leafy vegetables change the international normalized ratio (INR). The safest teaching is not to avoid these foods but to eat about the same amount each week, so that the warfarin dose can be matched to a stable diet. Her statement shows she understood this.
Why warfarin, not a newer anticoagulant
She has atrial fibrillation with moderate rheumatic mitral stenosis. In this group, the stroke risk is high and direct oral anticoagulants are not used; warfarin with regular INR monitoring is the standard. Her plan to switch later to a newer drug that needs no blood tests is therefore incorrect and shows a gap in understanding. Anticoagulation is also long term: stopping warfarin when the palpitations settle leaves the atria prone to clot, because the rhythm and the valve disease, not the symptom, determine the risk.
| Statement | Assessment | Reason |
|---|
| Same amount of green leafy vegetables each week | Correct | Stable vitamin K keeps the INR stable |
| Switch later to a newer drug without blood tests | Incorrect | DOACs are not used with moderate to severe rheumatic mitral stenosis |
| Stop warfarin when palpitations go away | Incorrect | Stroke risk persists; therapy is long term |
| Mefenamic acid for menstrual cramps | Incorrect | NSAIDs add to bleeding risk |
Drug interactions and bleeding risk
Mefenamic acid is a nonsteroidal anti-inflammatory drug. NSAIDs impair platelet function and irritate the stomach lining, so combined with warfarin they raise the risk of gastrointestinal and other bleeding. Paracetamol (acetaminophen) is the preferred analgesic for menstrual cramps unless her provider advises otherwise. Other teaching includes reporting bleeding signs such as dark stools, blood in the urine, heavy menstrual flow, or easy bruising, telling every provider and dentist that she takes warfarin, and keeping her scheduled INR checks.
Watch out! A common distractor tells clients to stop eating green vegetables. This is unnecessary and can make the INR unstable when the food is eaten again. Consistency, not avoidance, is the rule.
Exam takeaway
Key point! For warfarin teaching, look for consistent vitamin K intake, regular INR checks, avoidance of NSAIDs and unadvised supplements, and long-term use. In atrial fibrillation with moderate to severe rheumatic mitral stenosis, warfarin is required and DOACs are not substituted.