INR 6.4 the Night Before a Colonoscopy

Do not carry out the order as written; clarify it with the provider first.

• IV vitamin K 10 mg is a large dose for an asymptomatic elevation. It risks an anaphylactoid reaction with IV administration and can drive the INR below therapeutic range for days, creating a bridge of warfarin resistance and new thromboembolic risk in a patient with atrial fibrillation.
• He is not asymptomatic. Gum bleeding plus a dark, tarry stool suggests gastrointestinal bleeding, so this is not a 'high INR, no bleeding' situation. A melenic stool needs a hemoglobin, a repeat stool check, and a conversation about whether the colonoscopy should be diagnostic rather than elective with biopsy.
• The schedule conflicts with the drug. A biopsy tomorrow with an INR of 6.4 is not safe; the procedure timing has to be reconciled with reversal, not forced to fit.

What to do: Hold warfarin now (that part is safe and within protocol), notify the provider with the bleeding findings and the naproxen history, and ask for a targeted order - typically low-dose oral vitamin K (1 to 2.5 mg) rather than 10 mg IV, plus a CBC and a repeat INR in 12 to 24 hours. Give IV vitamin K only if ordered for major bleeding, and if it is given, administer slowly with monitoring. Do not give any intramuscular injections. Escalate to the provider on call if the ordering clinician is unreachable, and document the concern and the response.

Three interacting causes, at least two of them new:

• Amiodarone. It inhibits CYP2C9 and CYP3A4, the enzymes that clear S-warfarin, so warfarin concentrations rise even though the dose never changed. The effect is slow, which matches a jump occurring in the second week.
• Naproxen. An NSAID displaces warfarin from albumin and independently inhibits platelet aggregation and injures gastric mucosa - so it raises the free warfarin level and simultaneously makes bleeding more likely while causing the melena.
• Baseline factors. Age, low body weight, acute illness, reduced oral intake, and any change in vitamin K–rich foods all shift the INR.

History to add: missed or doubled warfarin doses; new prescriptions, especially antibiotics such as trimethoprim-sulfamethoxazole or metronidazole; herbal products and supplements; recent diarrhea or poor eating; alcohol intake; falls or head trauma; any other dark stools, gum or nose bleeding, or bruising; and whether he had the amiodarone dose changed.

Framing for the provider: 'His INR is 6.4 with two new bleeding findings and two new interacting drugs - amiodarone started ten days ago and naproxen this week. I have held the warfarin. I need a CBC and an INR plan, and I think we should reconsider biopsying tomorrow.'

Teach the why, so the rules stick.

• Warfarin: same time each day, never double a missed dose, no dose changes without an INR check. Explain that amiodarone will keep pushing his INR up and that his warfarin dose may need to be lower while he takes it.
• Pain relief: naproxen and other NSAIDs, including ibuprofen and aspirin-containing cold products, are off the table. Acetaminophen at a stated maximum is the safer choice, and he should check with the pharmacist before any over-the-counter purchase.
• Bleeding precautions: soft toothbrush, electric razor, gloves for yard work, no contact sports; know the warning signs - black or bloody stool, blood in urine, vomiting blood or coffee-ground material, severe or unusual headache, and any fall involving the head, which warrants immediate evaluation.
• Consistency: keep vitamin K–rich foods steady rather than eliminating them; a sudden drop or surge changes the INR.
• Monitoring: INR in two to three days, then per the anticoagulation clinic; keep every appointment. A wallet card or bracelet stating warfarin therapy.
• Procedure planning: tell every clinician, including the dentist, about warfarin before any procedure; never stop it on his own.
• Verification: use teach-back - have him state the three signs that would send him to the emergency department and which pain reliever he will use. Document what was taught, how he demonstrated understanding, and who was present.