Pharmacy Drug Interactions 2 — Questions and Answers
Question 1: A patient on warfarin starts taking aspirin. What is the primary concern?
- Decreased anticoagulation effect
- Increased risk of bleeding (Correct answer)
- Reduced pain relief
- Elevated blood pressure
Correct answer: Increased risk of bleeding
Aspirin inhibits platelet aggregation and may displace warfarin from protein binding sites, significantly increasing bleeding risk when combined.
Question 2: Which drug, when combined with an SSRI, can cause serotonin syndrome?
- Metformin
- Tramadol (Correct answer)
- Lisinopril
- Metoprolol
Correct answer: Tramadol
Tramadol inhibits serotonin reuptake; combining it with SSRIs can lead to excessive serotonin accumulation, causing serotonin syndrome.
Question 3: Grapefruit juice is known to inhibit which enzyme, causing elevated plasma levels of many drugs?
- CYP1A2
- CYP2D6
- CYP3A4 (Correct answer)
- CYP2C9
Correct answer: CYP3A4
Grapefruit juice inhibits intestinal CYP3A4, reducing first-pass metabolism of many drugs (e.g., statins, calcium channel blockers), increasing their plasma concentrations.
Question 4: Concurrent use of an ACE inhibitor and a potassium-sparing diuretic increases the risk of:
- Hypokalemia
- Hyperkalemia (Correct answer)
- Hyponatremia
- Hypernatremia
Correct answer: Hyperkalemia
Both ACE inhibitors (reduce aldosterone) and potassium-sparing diuretics (block aldosterone or sodium channels) retain potassium, leading to dangerous hyperkalemia.
Question 5: Ciprofloxacin should not be taken within 2 hours of antacids containing aluminum or magnesium because:
- The combination causes severe GI bleeding
- Cations chelate ciprofloxacin, reducing absorption (Correct answer)
- Ciprofloxacin becomes toxic in alkaline pH
- The interaction causes QT prolongation
Correct answer: Cations chelate ciprofloxacin, reducing absorption
Divalent and trivalent cations (Al³⁺, Mg²⁺, Ca²⁺, Fe²⁺, Zn²⁺) chelate fluoroquinolones, forming insoluble complexes that dramatically reduce oral absorption.
Question 6: What type of drug interaction occurs when two drugs with similar CNS depressant effects are combined?
- Antagonism
- Additive/synergistic effect (Correct answer)
- Induction
- Chelation
Correct answer: Additive/synergistic effect
Combining CNS depressants (e.g., opioids + benzodiazepines) produces additive or synergistic sedation, respiratory depression, and increased risk of overdose.
Pharmacy Drug Interactions 2
A patient on warfarin starts taking aspirin.
What is the primary concern?