PTCE - Medications (35% of the exam) - Section 1.3

Identify common or life-threatening drug interactions and contraindications, including drug-drug, drug-dietary supplement, drug-laboratory, drug-nutrient, and drug-disease interactions.

Identify clinically significant drug-drug, drug-dietary supplement, drug-nutrient, drug-laboratory, and drug-disease interactions and their underlying mechanisms. Distinguish interactions that are absolutely contraindicated from those requiring monitoring or dose adjustment.

Drug-drug interactionContraindicationDrug-dietary supplement interactionDrug-disease interaction

Practice question for this objective

Free sampleMedicationshard

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.

Identify that vitamin K supplements antagonise warfarin and that interactions of this kind require pharmacist referral, not technician dose advice. Warfarin works by inhibiting vitamin K epoxide reductase, lowering clotting factor synthesis. Supplemental vitamin K supplies the very cofactor warfarin suppresses, so it opposes the drug, reduces the INR, and raises clot risk, which is why the pharmacist must assess it.

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.

See more PTCE practice questions, answers explained.

Exam traps in Medications

Answers that look right on this material and are not. Each one is a distractor from a different question in the PTCE bank for this domain.

Advise the patient to take an over-the-counter antihistamine and continue the antibiotic course as prescribed
Why it is wrong: An oral antihistamine may help a mild rash, but the lip swelling and breathing difficulty signal a possible anaphylactic reaction that an antihistamine alone cannot manage, so continuing the drug is dangerous.
Opioid analgesics commonly cause increased urination as their single most characteristic effect on the body.
Why it is wrong: Tempting because opioids do affect many systems, but constipation rather than increased urination is the classic opioid side effect.
Sildenafil taken together with a daily multivitamin containing iron and zinc.
Why it is wrong: Multivitamins with minerals do not produce a clinically significant interaction with sildenafil, so this pairing is a distractor that sounds cautious but is not contraindicated.

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