Autonomic Pharmacology USMLE Step 1 Practice Question
A 72-year-old man with chronic constipation is prescribed loperamide for symptomatic relief. He takes oxybutynin daily for overactive bladder. Vital signs show BP 138/82, HR 78, RR 16, temperature 37.2°C, SpO2 98%. Abdominal examination reveals decreased bowel sounds. Recent CT abdomen shows no obstruction. He denies abdominal pain. Which of the following represents the primary pharmacologic concern when combining these anticholinergic and opioid medications?
Answer choices
- AIncreased opioid absorption leading to systemic toxicity
- BExcessive diarrhea from decreased parasympathetic tone
- CReduced efficacy of loperamide due to antagonistic effects
- DSevere constipation and ileus from additive anticholinergic and opioid effectsCorrect answer
- EEnhanced serotonin syndrome from opioid-anticholinergic interaction
- FIncreased urinary retention and acute kidney injury from combined anticholinergic effects
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