INR 6.4 in the anticoagulation clinic: a locum prescription, an amiodarone interaction and a queue outside
Mrs Wong, 68, weighs 52 kg and has an eGFR of 28 mL/min/1.73 m². She takes warfarin for atrial fibrillation (target INR 2.0–3.0), amiodarone 200 mg daily and furosemide 40 mg daily. At the nurse-led anticoagulation clinic her INR is 6.4; three weeks ago it was 2.6. She has no melaena or haematuria but reports gum bleeding when brushing her teeth and new bruises on both forearms. Two days ago a locum doctor prescribed co-trimoxazole 960 mg twice daily for a urinary tract infection, and she has also been taking a friend's herbal joint remedy. BP 148/86 mmHg, pulse 92 irregular, temperature 36.8 °C. The prescriber is uncontactable for the next two hours. The clinic protocol allows the nurse to withhold warfarin and to give oral phytomenadione 1–3 mg after medical review; vitamin K 10 mg ampoules and intravenous access equipment are available. The next patient is already waiting.
1. Interpret the INR and decide what the nurse should do in the next hour, giving the reasoning behind each action.
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Interpretation. An INR of 6.4 with a recent baseline of 2.6 means anticoagulation is far outside the therapeutic range and spontaneous bleeding risk is high, even though there is no major bleeding now. Minor bleeding (gums, bruising) plus age, renal impairment and a likely drug interaction put her in a higher-risk group.
Immediate actions:
- Withhold the next warfarin dose and document it. This is within the protocol.
- Do a focused bleeding assessment: neurological symptoms and headache, vision, urine, stool colour, abdominal or flank pain, joint swelling, new bruising, and postural symptoms. Check BP and pulse again and record a full set of observations.
- Do not give intramuscular injections or any NSAID or aspirin-containing product.
- Arrange a repeat INR in 24–48 hours, and alert the haematology or medical team now rather than waiting for the prescriber.
- Low-dose oral vitamin K is not automatically indicated when there is no major bleeding; it is considered for high bleeding risk, and the protocol requires medical review before giving it. Prepare the case for that review; keep IV access equipment available but do not insert a cannula reflexively.
Look for the cause, because it changes the plan: co-trimoxazole inhibits CYP2C9 metabolism of S-warfarin, displaces protein binding and reduces gut vitamin K synthesis; amiodarone has a very long half-life and also inhibits warfarin metabolism; the herbal remedy is an unknown quantity; reduced dietary intake or diarrhoea would add to the effect.
2. The prescriber cannot be reached. What should the nurse communicate, to whom, and what should the patient be taught before she leaves?
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Escalation rather than silence.
- Contact the clinic's nominated medical cover or the on-call haematology or medical team, using SBAR: INR 6.4, baseline 2.6, co-trimoxazole started two days ago, amiodarone, herbal remedy, eGFR 28, minor bleeding only.
- Ask specifically: should the co-trimoxazole be changed, when should warfarin restart and at what dose, and is oral vitamin K indicated?
- If no doctor can be reached, escalate to the nurse-in-charge of the clinic and follow the written policy for out-of-range results; do not simply send her home with an unaddressed INR of 6.4.
- Document the times, names and advice, and complete an incident report because a significant interaction was prescribed without anticoagulation review.
Patient teaching - specific, not generic:
- What to do tonight: no warfarin until told, no alcohol binges, no new over-the-counter or herbal products without checking, use a soft toothbrush.
- Red flags to return immediately: black or bloody stool, red or brown urine, vomiting blood, severe headache, weakness or confusion, a fall, uncontrolled nosebleed.
- Explain the interaction in plain language: 'The new antibiotic raises your INR, which is why you are bruising and your gums bleed.'
- Give written contact numbers, confirm her next INR appointment, and ask her to show her anticoagulant card to any clinician, including dentists.
- Check understanding with teach-back, not 'Do you understand?'
3. The clinic is running 40 minutes late and a health care assistant is available. What can be delegated to the assistant, and what must remain with the registered nurse?
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The principle: delegation transfers the task, not the accountability. The registered nurse remains answerable for the assessment, the interpretation of results, the decision about warfarin and vitamin K, and the patient education.
Can be delegated, with clear instructions and a named supervisor:
- Escorting Mrs Wong to the waiting area and checking her into the queue.
- Measuring and recording height, weight, blood pressure and pulse, provided the assistant knows to report a systolic below 100 mmHg, a pulse above 110 or any dizziness immediately.
- Preparing the room, restocking vitamin K, printing the repeat INR request, and phoning the pharmacy to check whether a different antibiotic is available.
- Making the follow-up appointment and giving the printed bleeding-advice leaflet that the nurse has already explained.
Must remain with the registered nurse:
- Interpreting the INR and deciding to withhold warfarin.
- The bleeding assessment and the decision to seek medical review for vitamin K.
- The conversation with the prescriber or medical cover.
- Teaching about interactions and red flags, and the final check that Mrs Wong understands.
- Documentation and the incident report.
Do not delegate to an assistant who has not been assessed as competent for the task, and do not let the queue become the reason a critical INR is left unaddressed; a 40-minute delay is a staffing problem to escalate to the clinic manager, not a clinical compromise.