A patient, Desmond Achterberg, has been stabilised on warfarin for atrial fibrillation with a target INR of 2 to 3. He tells the technician at pick-up that he has started taking a daily high-dose vitamin K supplement he bought to support bone health. What is the technician's BEST response?
- AReassure him that supplements do not affect prescription medicines and complete the sale.
- BRefer him to the pharmacist, because high-dose vitamin K can reduce warfarin's effect and lower the INR. Correct
- CTell him to stop the warfarin while taking the supplement and resume it when the bottle is finished.
- DAdvise him to double his warfarin dose to overcome the supplement's effect.
Why A is wrong: This is tempting because supplements are sold over the counter and seem benign, but vitamin K directly antagonises warfarin, so dismissing the interaction is unsafe and wrong.
Why B is correct: Vitamin K is the substrate warfarin blocks, so a high-dose supplement opposes warfarin, can drop the INR below range, and warrants a pharmacist counselling referral, making this the best action.
Why C is wrong: Stopping an anticoagulant sounds like a way to avoid the interaction, but halting warfarin risks clot formation and is outside the technician's scope, so this is wrong.
Why D is wrong: Increasing the dose seems to logically counter the antagonism, but dose changes require prescriber and pharmacist judgement and self-adjustment risks bleeding, so a technician must not advise this.