Warfarin counselling and INR monitoring

PLAB 2 & PRES 3 · pharmacology · medium · 8 minutes

Candidate brief

You are a doctor in a cardiology follow-up clinic. Mr Patrick Doyle, 58, recently had a mechanical mitral valve replacement and has been prescribed lifelong warfarin. His anticoagulation clinic has documented a target INR range of 2.5 to 3.5. His INR today is 2.8. Explain why he needs warfarin, how it is monitored and the important safety advice. Address his questions and concerns. No physical examination is required.

What examiners look for

Warfarin is appropriate in this scenario because the patient has a mechanical heart valve. Do not suggest switching a patient with a mechanical valve to a DOAC such as apixaban or rivaroxaban. INR monitoring checks whether anticoagulation is within the patient’s documented target range. A low INR increases the risk of clotting, while a high INR increases the risk of bleeding. The target depends on the indication, valve type, valve position and patient factors. The patient should take the exact written dose at the same time each day, attend INR tests and never adjust or stop warfarin without professional advice. If a dose is remembered on the same day, it can usually be taken then. If it is not remembered until the next day, skip it and continue normally. Never double the dose. Do not tell patients to avoid green vegetables. Advise a healthy diet with a reasonably consistent vitamin K intake. Check before starting or stopping prescribed, over-the-counter or herbal medicines. Avoid non-prescribed NSAIDs and aspirin unless specifically authorised. Significant bleeding, neurological symptoms, collapse or a head injury require urgent medical assessment. Patients must inform healthcare professionals before surgery, dental treatment or other procedures and must not stop warfarin by themselves.

Guideline references

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