PTCB Quiz Prep

Drug Interaction Practice Questions with Answers

Updated · aligned to the 2026 PTCE outline

Drug-drug, drug-food and drug-disease interactions, and the counseling points that go with them.

10 questionsAnswers includedUntimedEvery answer cited100% free

Key takeaways

  • Three categories get tested: drug-drug, drug-food, and drug-disease.
  • Warfarin interacts with a long list including NSAIDs, antibiotics and vitamin K rich foods.
  • Grapefruit juice inhibits CYP3A4, raising levels of several statins and other substrates.
  • A technician flags an interaction alert for the pharmacist rather than resolving it.

Interaction questions on the PTCE are less about pharmacology than about pattern recognition: which combinations trigger an alert, and what the technician does when one fires. The classic pairs recur because they are clinically significant and well documented.

These sit in the Medications domain, which is 35% of the 2026 exam and the largest single block on it.

Want the same material as a timed, randomized run instead? Try the timed Medications practice test, the Medications domain guide, and the drug class guides.

All 10 drug interactions questions and answers

Each answer is followed by an explanation and a link to the primary source it was checked against.

  1. 1. A patient on warfarin brings a bottle of OTC ibuprofen to the register. Why should the technician alert the pharmacist?

    • A.Ibuprofen blocks warfarin absorption, causing clots
    • B.Ibuprofen turns warfarin into an inactive metabolite
    • C.Taking an NSAID with warfarin increases the risk of serious bleeding
    • D.The combination causes severe hypertension

    Answer: C. Taking an NSAID with warfarin increases the risk of serious bleeding

    Warfarin can cause serious, even fatal bleeding, and NSAIDs such as ibuprofen or naproxen add to that bleeding risk, so the combination needs pharmacist review. The interaction increases bleeding rather than clotting, which makes the absorption-and-clots option exactly backwards.

    Source: medlineplus.gov

  2. 2. A patient's profile shows sublingual nitroglycerin for angina. A new prescription for sildenafil arrives. What should happen?

    • A.Fill both; the drugs work on different body systems
    • B.Fill both but counsel the patient to separate the doses by 2 hours
    • C.Dispense a lower sildenafil dose without contacting anyone
    • D.Flag the prescription; sildenafil is contraindicated with nitrates because of the risk of severe hypotension

    Answer: D. Flag the prescription; sildenafil is contraindicated with nitrates because of the risk of severe hypotension

    Sildenafil is contraindicated with organic nitrates in any form, taken regularly or intermittently, because together they can cause a dangerous drop in blood pressure. Separating the doses by a couple of hours does not remove the contraindication, so that option understates the danger.

    Source: dailymed.nlm.nih.gov

  3. 3. Drinking large amounts of grapefruit juice while taking simvastatin can cause which problem?

    • A.Too much of the statin stays in the body, raising the risk of liver and muscle damage
    • B.The statin is destroyed before it can be absorbed
    • C.The juice makes the statin bind to dietary fat
    • D.Blood cholesterol rises immediately

    Answer: A. Too much of the statin stays in the body, raising the risk of liver and muscle damage

    Grapefruit juice blocks intestinal CYP3A4, the enzyme that normally metabolizes statins like simvastatin and atorvastatin, so more drug enters the blood and stays in the body longer, increasing the risk of liver and muscle damage. The interaction raises drug levels rather than destroying the drug, so the reduced-absorption option gets the direction wrong.

    Source: fda.gov

  4. 4. A patient taking ciprofloxacin also uses a calcium-containing antacid (Tums) after meals. How should the two be scheduled?

    • A.Take them together to reduce stomach upset
    • B.Take ciprofloxacin at least 2 hours before or 6 hours after the antacid
    • C.Take ciprofloxacin 30 minutes after the antacid
    • D.Stop the antacid permanently; the two can never be used in the same month

    Answer: B. Take ciprofloxacin at least 2 hours before or 6 hours after the antacid

    Calcium, aluminum, and magnesium antacids, as well as calcium, iron, or zinc supplements and sucralfate, bind ciprofloxacin in the gut and block its absorption, so ciprofloxacin should be taken at least 2 hours before or 6 hours after them. Taking the drugs together defeats the antibiotic, and a 30-minute gap is far too short to avoid chelation.

    Source: medlineplus.gov

  5. 5. A patient starting phenelzine, an MAOI, should be counseled to avoid which foods to prevent a serious reaction?

    • A.Fresh salads and raw vegetables
    • B.Dairy products such as fresh milk and yogurt
    • C.Aged or smoked cheeses and meats and other tyramine-rich fermented foods
    • D.Citrus fruits and fruit juices

    Answer: C. Aged or smoked cheeses and meats and other tyramine-rich fermented foods

    Foods that are aged, smoked, fermented, improperly stored, or spoiled are high in tyramine, and eating them during phenelzine treatment can trigger a serious reaction. Fresh dairy such as milk is the tempting wrong answer, but the danger comes from aging and fermentation, not dairy itself.

    Source: medlineplus.gov

  6. 6. A patient is stopping an MAOI prescribed for depression. Per the fluoxetine labeling, how long must they wait after the last MAOI dose before starting fluoxetine?

    • A.At least 14 days
    • B.At least 5 weeks
    • C.24 hours
    • D.No waiting period is needed

    Answer: A. At least 14 days

    Fluoxetine must not be started within 14 days of stopping an MAOI intended to treat psychiatric disorders because of the risk of serotonin syndrome. The 5-week figure applies in the opposite direction: an MAOI must not be started within 5 weeks of stopping fluoxetine, because fluoxetine's active metabolite persists that long.

    Source: dailymed.nlm.nih.gov

  7. 7. A patient takes levothyroxine each morning and wants to add a calcium carbonate supplement. What administration advice reflects the levothyroxine labeling?

    • A.Take both together with breakfast for convenience
    • B.Take the calcium 30 minutes after the levothyroxine
    • C.Alternate the two drugs on different days
    • D.Separate levothyroxine from the calcium supplement by at least 4 hours

    Answer: D. Separate levothyroxine from the calcium supplement by at least 4 hours

    Calcium carbonate can form an insoluble chelate with levothyroxine, and iron behaves similarly, reducing thyroid hormone absorption and potentially causing hypothyroidism; the label directs administering levothyroxine at least 4 hours apart from these agents. A 30-minute gap is far too short to prevent the binding interaction.

    Source: dailymed.nlm.nih.gov

  8. 8. A patient finishing a course of metronidazole asks when they can safely drink wine again. What is the correct counseling point?

    • A.Alcohol is fine as long as it is taken with food
    • B.Avoid alcohol while taking metronidazole and for at least 3 days after the final dose
    • C.Wait 24 hours after the last dose
    • D.Only beer must be avoided; wine is safe

    Answer: B. Avoid alcohol while taking metronidazole and for at least 3 days after the final dose

    Alcohol and products containing propylene glycol must be avoided during metronidazole therapy and for at least 3 days after the final dose, because the combination can cause nausea, vomiting, stomach cramps, headache, sweating, and flushing. A 24-hour wait is too short since the reaction can still occur days after the last dose.

    Source: medlineplus.gov

  9. 9. A patient takes digoxin along with furosemide, a potassium-depleting diuretic, and has not been taking the prescribed potassium supplement. Why is this combination a concern?

    • A.Furosemide blocks digoxin absorption in the gut
    • B.The combination causes severe hyperkalemia
    • C.Potassium depletion from the diuretic is a major contributing factor to digoxin (digitalis) toxicity
    • D.Digoxin cancels the diuretic effect of furosemide

    Answer: C. Potassium depletion from the diuretic is a major contributing factor to digoxin (digitalis) toxicity

    Digoxin labeling identifies potassium-depleting diuretics as a major contributing factor to digitalis toxicity, since low potassium sensitizes the heart to digoxin's effects. The hyperkalemia option is the reverse of what happens; loop diuretics waste potassium rather than raise it.

    Source: dailymed.nlm.nih.gov

  10. 10. A patient taking spironolactone mentions using a potassium-containing salt substitute at home. What risk does this combination raise?

    • A.Hyperkalemia (dangerously high potassium levels)
    • B.Hypokalemia (dangerously low potassium levels)
    • C.Reduced diuretic effect requiring a higher dose
    • D.Severe sodium retention and edema

    Answer: A. Hyperkalemia (dangerously high potassium levels)

    Spironolactone itself can cause hyperkalemia, and the labeling warns the risk is increased by potassium supplementation, potassium-containing salt substitutes, or other potassium-raising drugs like ACE inhibitors and ARBs. Hypokalemia is the wrong direction; spironolactone is potassium-sparing, unlike loop or thiazide diuretics.

    Source: dailymed.nlm.nih.gov

Drug Interactions: FAQ

What are the three types of drug interaction?

Drug-drug, where two medications affect each other; drug-food, where a food or beverage alters absorption or metabolism; and drug-disease, where a drug worsens an existing condition. The PTCE draws from all three.

Can a pharmacy technician override an interaction alert?

No. Clinical judgment on an interaction belongs to the pharmacist. The technician's role is to make sure the alert reaches the pharmacist and that the patient's profile, including allergies and current medications, is accurate enough for the screening to work.

Why does grapefruit juice matter?

It inhibits the CYP3A4 enzyme in the intestinal wall, which slows the metabolism of drugs that rely on it. Blood levels rise, and for drugs like simvastatin and certain calcium channel blockers that can push a normal dose into a toxic range.

Official sources checked

Every answer above was written against a primary source and verified independently. These are the 10 sources behind this set.

More practice question sets

Sig CodesHigh-Alert MedicationsLASA DrugsError ReportingStorage & ExpirationBilling & InsuranceControlled Substances

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