Ptcb Quiz: Drug Interactions
20 questions · exam conditions
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Drug InteractionsQuestion 1 of 20

A patient's profile shows they are taking warfarin. A new prescription for sulfamethoxazole/trimethoprim is entered. The computer system flags a potential interaction. This interaction increases the risk of which of the following?

Bleeding
Clotting
Hypertension
Kidney damage
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Ptcb Quiz

Ptcb Quiz: Drug Interactions

Practice Drug Interactions in Ptcb with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Drug Interactions, giving you a quick way to practice the rules, question types, and explanations that matter most for Ptcb.

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Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

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Question 1

A patient's profile shows they are taking warfarin. A new prescription for sulfamethoxazole/trimethoprim is entered. The computer system flags a potential interaction. This interaction increases the risk of which of the following?

  1. Bleeding (correct answer)
  2. Clotting
  3. Hypertension
  4. Kidney damage
Explanation: Sulfamethoxazole/trimethoprim can significantly inhibit the metabolism of warfarin, leading to an elevated International Normalized Ratio (INR) and a substantially increased risk of bleeding. The pharmacy technician should always alert the pharmacist to this critical interaction.

Question 2

A patient brings in a new prescription for sildenafil. The technician checks the patient's profile and sees an active prescription for nitroglycerin. This combination is absolutely contraindicated due to the risk of what severe adverse effect?

  1. Severe hypotension (correct answer)
  2. Serotonin syndrome
  3. Hypertensive crisis
  4. Acute kidney injury
Explanation: Both sildenafil (a PDE-5 inhibitor) and nitroglycerin (a nitrate) are potent vasodilators. When used together, they can cause a synergistic effect, leading to a profound and life-threatening drop in blood pressure (severe hypotension).

Question 3

A medication order for lisinopril is being filled for a patient who also buys over-the-counter potassium chloride supplements. The combination of these two products can lead to a dangerously high level of potassium in the blood, a condition known as:

  1. Hyperkalemia (correct answer)
  2. Hypokalemia
  3. Hyponatremia
  4. Hypernatremia
Explanation: ACE inhibitors like lisinopril can increase potassium levels. Taking them with potassium supplements can lead to hyperkalemia (high potassium), which can cause serious cardiac arrhythmias. Hypokalemia is low potassium, while hyponatremia and hypernatremia refer to sodium levels.

Question 4

A patient who takes sertraline daily receives a new prescription for sumatriptan to be taken as needed for migraines. The pharmacy computer system flags an interaction warning. This combination increases the risk of:

  1. Serotonin syndrome (correct answer)
  2. QTc prolongation
  3. Stevens-Johnson syndrome
  4. Hypertensive crisis
Explanation: Both SSRIs (like sertraline) and triptans (like sumatriptan) increase levels of serotonin in the brain. Using them concurrently can lead to an excessive accumulation of serotonin, causing a potentially life-threatening condition called serotonin syndrome, characterized by agitation, confusion, rapid heart rate, and fever.

Question 5

A patient is taking both digoxin and furosemide. Furosemide can deplete potassium levels in the body. How does low potassium (hypokalemia) affect the patient taking digoxin?

  1. It increases the risk of digoxin toxicity. (correct answer)
  2. It decreases the absorption of digoxin.
  3. It causes the digoxin to be eliminated too quickly.
  4. It cancels out the therapeutic effect of digoxin.
Explanation: Digoxin exerts its effect by binding to the Na+/K+ ATPase pump in heart muscle cells, a site where potassium also binds. When potassium levels are low (hypokalemia), there is less competition for these binding sites, allowing more digoxin to bind. This enhances digoxin's effects and greatly increases the risk of toxicity, even at therapeutic drug levels.

Question 6

When reviewing a medication profile for a patient on warfarin, the technician sees a note that the patient also takes ginkgo biloba supplements. This combination is concerning because it can increase the patient's risk of:

  1. Bleeding (correct answer)
  2. Thrombosis
  3. Liver damage
  4. Serotonin syndrome
Explanation: Warfarin is an anticoagulant that prevents blood clots. Ginkgo biloba is an herbal supplement that can inhibit platelet aggregation, which also impairs clotting. Using them together has an additive effect, increasing the risk of spontaneous or excessive bleeding.

Question 7

A pharmacist should be alerted if a patient with severe chronic kidney disease (CKD) receives a prescription for metformin. The primary risk associated with using metformin in this patient population is:

  1. Lactic acidosis (correct answer)
  2. Severe hypoglycemia
  3. Acute pancreatitis
  4. Worsening of kidney function
Explanation: Metformin is eliminated from the body by the kidneys. In patients with severe renal impairment, the drug is not cleared effectively and can accumulate to toxic levels. This accumulation increases the risk of lactic acidosis, a rare but very serious metabolic complication with a high mortality rate.

Question 8

A patient taking levothyroxine for hypothyroidism is instructed to separate the administration of their thyroid medication from their daily iron supplement by at least four hours. This is because iron can:

  1. Decrease the absorption of levothyroxine. (correct answer)
  2. Increase the metabolism of levothyroxine.
  3. Cause a toxic buildup of levothyroxine.
  4. Inactivate the iron supplement.
Explanation: Iron salts can bind to levothyroxine in the gut, forming a non-absorbable complex. This significantly reduces the amount of levothyroxine that enters the bloodstream, leading to decreased efficacy and potentially uncontrolled hypothyroidism. Similar interactions occur with calcium and aluminum-containing antacids.

Question 9

A patient taking azathioprine receives a new prescription for allopurinol. The computer flags a major interaction. What is the consequence of this drug combination if the azathioprine dose is not significantly reduced?

  1. Increased risk of bone marrow suppression (correct answer)
  2. Complete loss of allopurinol's effect
  3. Severe hypertensive crisis
  4. Rapid development of kidney stones
Explanation: Allopurinol inhibits xanthine oxidase, an enzyme that is essential for the metabolism of azathioprine. Co-administration without a significant dose reduction of azathioprine (often by 66-75%) can lead to toxic levels of the immunosuppressant, resulting in severe and life-threatening bone marrow suppression.

Question 10

A patient prescribed spironolactone for heart failure mentions using a salt substitute that contains potassium chloride. This combination should be flagged for the pharmacist because it increases the risk of:

  1. Hyperkalemia (correct answer)
  2. Hyponatremia
  3. Dehydration
  4. Hypotension
Explanation: Spironolactone is a potassium-sparing diuretic, which works by blocking aldosterone and causing the body to retain potassium. Salt substitutes often replace sodium chloride with potassium chloride. Combining these two sources of potassium can lead to dangerously high blood potassium levels (hyperkalemia), which can cause life-threatening heart rhythm problems.

Question 11

A patient receiving a prescription for phenelzine should be counseled to avoid foods rich in tyramine, such as aged cheeses and cured meats. Consuming these foods while taking this medication can cause what type of adverse reaction?

  1. Hypertensive crisis (correct answer)
  2. Severe sedation
  3. Hypoglycemic shock
  4. Liver failure
Explanation: Phenelzine is a Monoamine Oxidase Inhibitor (MAOI). MAOIs prevent the breakdown of tyramine. An excess of tyramine can cause a massive release of catecholamines, leading to a rapid and dangerous increase in blood pressure known as a hypertensive crisis.

Question 12

A technician sees a prescription for hydrochlorothiazide for a patient with a documented history of gout. Why might this be a potential drug-disease interaction?

  1. Thiazide diuretics can increase uric acid levels. (correct answer)
  2. Thiazide diuretics are a common cause of allergic joint pain.
  3. Patients with gout rapidly metabolize thiazide diuretics.
  4. The combination increases the risk of kidney stones.
Explanation: Thiazide diuretics, such as hydrochlorothiazide, can decrease the kidneys' ability to excrete uric acid. This leads to an increase in uric acid levels in the blood (hyperuricemia). In patients who are already susceptible to gout, this elevated level can trigger a painful acute gout flare.

Question 13

A patient mentions she has started taking St. John's wort, an over-the-counter herbal supplement for mood. Her medication profile includes an oral contraceptive. What is the most significant potential interaction the technician should recognize?

  1. Decreased effectiveness of the oral contraceptive. (correct answer)
  2. Increased risk of blood clots.
  3. Increased risk of serotonin syndrome.
  4. Severe nausea and vomiting.
Explanation: St. John's wort is a potent inducer of the CYP3A4 enzyme system. This enzyme metabolizes the hormones in oral contraceptives. By inducing the enzyme, St. John's wort speeds up the breakdown of the hormones, lowering their blood levels and potentially leading to unintended pregnancy.

Question 14

A patient taking atorvastatin for high cholesterol mentions they drink a large glass of grapefruit juice every morning. Why should the pharmacy technician alert the pharmacist to this information?

  1. Grapefruit juice increases the risk of muscle pain and damage. (correct answer)
  2. Grapefruit juice decreases the effectiveness of the atorvastatin.
  3. Grapefruit juice can cause a dangerous increase in blood pressure.
  4. Grapefruit juice can lead to high blood sugar levels.
Explanation: Grapefruit juice is a strong inhibitor of the CYP3A4 enzyme, which is responsible for metabolizing atorvastatin. This interaction leads to higher concentrations of the statin in the blood, increasing the risk of adverse effects, including myopathy (muscle pain) and potentially life-threatening rhabdomyolysis (muscle breakdown).

Question 15

A patient is prescribed doxycycline and is advised to take it one hour before or two hours after taking their daily calcium carbonate antacid. What is the reason for this specific timing instruction?

  1. Calcium binds to doxycycline, decreasing its absorption. (correct answer)
  2. The antacid increases stomach pH, destroying the doxycycline.
  3. Doxycycline increases the side effects of the antacid.
  4. The combination can lead to toxic levels of calcium.
Explanation: Polyvalent cations like calcium, magnesium, aluminum, and iron can bind to tetracycline antibiotics (like doxycycline) in the gastrointestinal tract. This process, called chelation, forms an insoluble complex that is not well absorbed, reducing the antibiotic's effectiveness.

Question 16

A patient stabilized on warfarin is started on amiodarone for an arrhythmia. Why must the patient's warfarin therapy be closely monitored and likely adjusted?

  1. Amiodarone inhibits the metabolism of warfarin, increasing its effect. (correct answer)
  2. Amiodarone induces the metabolism of warfarin, decreasing its effect.
  3. Both drugs compete for protein binding, making warfarin less effective.
  4. Amiodarone directly counteracts the anticoagulant effect of warfarin.
Explanation: Amiodarone is a potent inhibitor of several cytochrome P450 enzymes, including CYP2C9, which is the primary enzyme that metabolizes the S-isomer of warfarin. This inhibition slows down the clearance of warfarin, leading to higher blood levels and an increased INR, which elevates the risk of bleeding. The warfarin dose typically needs to be reduced.

Question 17

A prescription for ciprofloxacin is being dispensed. The patient should be advised to avoid taking the antibiotic at the same time as which of the following?

  1. Milk or yogurt (correct answer)
  2. Grapefruit juice
  3. High-fat meals
  4. Caffeinated beverages
Explanation: Fluoroquinolone antibiotics like ciprofloxacin can bind with polyvalent cations, such as the calcium found in dairy products (milk, yogurt, cheese) and calcium-fortified juices. This chelation process forms an insoluble compound, significantly reducing the absorption of the antibiotic and potentially leading to treatment failure.

Question 18

A patient with a known history of asthma is prescribed propranolol for migraine prevention. This is a potential drug-disease interaction because non-selective beta-blockers like propranolol can cause:

  1. Bronchoconstriction (correct answer)
  2. Tachycardia
  3. Hypertension
  4. Hyperglycemia
Explanation: Non-selective beta-blockers block both beta-1 (in the heart) and beta-2 (in the lungs) receptors. Blocking beta-2 receptors can cause the airways to narrow (bronchoconstriction), which can trigger a severe, potentially fatal asthma attack in susceptible individuals.

Question 19

A patient with a history of uncontrolled hypertension asks to purchase an over-the-counter cold medication containing pseudoephedrine. Why is this a concern?

  1. Pseudoephedrine can increase blood pressure. (correct answer)
  2. Pseudoephedrine can cause drowsiness, masking hypertension symptoms.
  3. Pseudoephedrine interacts with most blood pressure medications.
  4. Pseudoephedrine is ineffective in patients with hypertension.
Explanation: Pseudoephedrine is a sympathomimetic agent that acts as a vasoconstrictor, meaning it narrows blood vessels. This action can lead to a significant increase in both systolic and diastolic blood pressure, which is particularly dangerous for individuals with pre-existing or uncontrolled hypertension.

Question 20

A pharmacy technician notes a high-dose, long-term prescription for ibuprofen for a patient with a diagnosis of chronic kidney disease (CKD). Why should this be brought to the pharmacist's attention?

  1. NSAIDs can worsen kidney function. (correct answer)
  2. NSAIDs are less effective in patients with CKD.
  3. Patients with CKD are more likely to have an allergic reaction to NSAIDs.
  4. NSAIDs are known to cause severe hyperkalemia.
Explanation: Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen work by inhibiting prostaglandins. Prostaglandins are vital for maintaining adequate blood flow to the kidneys. In patients with compromised renal function, NSAIDs can constrict blood vessels in the kidneys, leading to a further decline in kidney function or acute kidney injury.