NAPLEX QBANK Drug Interactions and Adverse Effects 1 — Questions and Answers
Question 1: A patient stabilized on an SSRI is prescribed tramadol for acute pain. Which serious adverse reaction is most likely to result from this combination?
- Neuroleptic malignant syndrome
- Serotonin syndrome (Correct answer)
- Anticholinergic toxicity
- Extrapyramidal effects
Correct answer: Serotonin syndrome
Both SSRIs and tramadol increase serotonergic activity, and their concurrent use can precipitate serotonin syndrome characterized by hyperthermia, autonomic instability, and neuromuscular abnormalities.
Question 2: A patient stabilized on warfarin begins amiodarone therapy for atrial fibrillation. What dose adjustment to warfarin is typically required?
- Increase warfarin dose by 50%
- Decrease warfarin dose by 30–50% (Correct answer)
- No dose adjustment is needed
- Discontinue warfarin immediately
Correct answer: Decrease warfarin dose by 30–50%
Amiodarone inhibits CYP2C9, the primary enzyme responsible for metabolizing warfarin's active S-enantiomer, resulting in elevated INR and requiring a 30–50% reduction in warfarin dose.
Question 3: Which antibiotic class most significantly inhibits CYP3A4 and increases the risk of statin-induced rhabdomyolysis?
- Fluoroquinolones
- Macrolides (Correct answer)
- Tetracyclines
- Sulfonamides
Correct answer: Macrolides
Macrolides such as clarithromycin and erythromycin inhibit CYP3A4, reducing statin metabolism, elevating plasma statin concentrations, and markedly increasing the risk of myopathy and rhabdomyolysis.
Question 4: What is the primary mechanism by which NSAIDs increase the toxicity of low-dose methotrexate?
- Inducing methotrexate hepatic metabolism
- Competing with methotrexate for renal tubular secretion (Correct answer)
- Displacing methotrexate from plasma protein binding sites
- Increasing GI absorption of methotrexate
Correct answer: Competing with methotrexate for renal tubular secretion
NSAIDs compete with methotrexate for renal tubular secretion via OAT transporters, reducing its elimination and causing dangerous accumulation and toxicity.
Question 5: Which drug combination is most likely responsible for a patient developing a prolonged QTc interval on ECG?
- Metoprolol and lisinopril
- Azithromycin and haloperidol (Correct answer)
- Metformin and glipizide
- Amlodipine and atorvastatin
Correct answer: Azithromycin and haloperidol
Both azithromycin and haloperidol independently prolong the QT interval by blocking cardiac hERG potassium channels; their combination synergistically increases the risk of torsades de pointes.
Question 6: A patient maintained on lithium for bipolar disorder begins taking ibuprofen regularly for arthritis pain. What effect on lithium levels is expected?
- Lithium levels will decrease
- Lithium levels will remain unchanged
- Lithium levels will increase (Correct answer)
- Lithium half-life will shorten significantly
Correct answer: Lithium levels will increase
NSAIDs inhibit prostaglandin-mediated renal vasodilation, reducing renal blood flow and lithium clearance, which raises serum lithium levels and increases the risk of toxicity.
Question 7: Which adverse effect is characteristic of ACE inhibitors but is NOT shared by angiotensin receptor blockers (ARBs)?
- Hyperkalemia
- Dry, persistent cough (Correct answer)
- First-dose hypotension
- Renal impairment
Correct answer: Dry, persistent cough
ACE inhibitors prevent bradykinin degradation, causing its accumulation in the airways and resulting in a dry, persistent cough; ARBs do not affect bradykinin metabolism.
NAPLEX QBANK Drug Interactions and Adverse Effects 1
A patient stabilized on an SSRI is prescribed tramadol for acute pain.
Which serious adverse reaction is most likely to result from this combination?