A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 68-year-old man presents with urinary retention for the past week. He says his symptoms onset gradually almost immediately after being prescribed a new medication for his depression. He states that he has increased his fluid intake to try to help the issue, but this has been ineffective. He also mentions that he has been having problems with constipation and dry mouth. His past medical history is significant for major depressive disorder, diagnosed 6 months ago. The patient denies any history of smoking, alcohol consumption, or recreational drug use. He is afebrile, and his vital signs are within normal limits. A physical examination is unremarkable. A urinalysis is normal. Which of the following medications was this patient most likely prescribed for his depression?
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A
PhenelzineIncorrect. Phenelzine (MAOI) causes hypertensive crisis with tyramine-containing foods, orthostatic hypotension, and serotonin syndrome with SSRIs - not anticholinergic urinary retention.
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B
MirtazapineIncorrect. Mirtazapine causes sedation and weight gain (H1 antagonism) and rare agranulocytosis - not the anticholinergic triad of dry mouth/constipation/urinary retention.
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C
AmitriptylineCorrect. Amitriptyline (tertiary amine TCA) has potent muscarinic antagonism causing the anticholinergic triad of urinary retention, constipation, and dry mouth.
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D
VenlafaxineIncorrect. Venlafaxine (SNRI) commonly causes hypertension, nausea, and discontinuation syndrome but is not strongly anticholinergic.
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E
FluoxetineIncorrect. Fluoxetine is an SSRI; its common adverse effects are sexual dysfunction, GI upset, and serotonin syndrome - not the anticholinergic triad of urinary retention, constipation, and dry mouth.
↑ Tap an answer to reveal the reasoning
Answer: C. This 68-year-old man started a new antidepressant 6 months ago for major depressive disorder and now has urinary retention, constipation, and dry mouth - the classic anticholinergic side-effect triad. The medication causing this constellation is amitriptyline, a tertiary amine tricyclic antidepressant (TCA) with potent muscarinic receptor antagonism.
TCAs (especially the tertiary amines amitriptyline, imipramine, doxepin) block multiple receptors: (1) muscarinic M1-3 (anticholinergic side effects - dry mouth, blurred vision, constipation, urinary retention, tachycardia, delirium in the elderly), (2) histamine H1 (sedation, weight gain), (3) alpha-1 adrenergic (orthostatic hypotension), and (4) cardiac sodium channels in overdose (wide QRS, ventricular arrhythmias - the most lethal feature of TCA toxicity). Their primary therapeutic mechanism is inhibition of serotonin and norepinephrine reuptake. Elderly patients are particularly vulnerable to anticholinergic burden - urinary retention in an older man (with likely BPH) is a classic complication, and TCAs are on the Beers Criteria 'potentially inappropriate in the elderly' list for this reason.
Distractors: phenelzine is an MAO inhibitor; side effects include hypertensive crisis with tyramine, orthostatic hypotension, and serotonin syndrome with serotonergic drugs - not anticholinergic. Mirtazapine causes sedation, weight gain (H1 antagonism), and rare agranulocytosis - not anticholinergic. Venlafaxine is an SNRI that can cause hypertension and discontinuation syndrome but is not strongly anticholinergic.
**Why each option:**
**A.** Wrong. Phenelzine (MAOI) causes hypertensive crisis with tyramine-containing foods, orthostatic hypotension, and serotonin syndrome with SSRIs - not anticholinergic urinary retention.
**B.** Wrong. Mirtazapine causes sedation and weight gain (H1 antagonism) and rare agranulocytosis - not the anticholinergic triad of dry mouth/constipation/urinary retention.
**C.** Correct. Amitriptyline (tertiary amine TCA) has potent muscarinic antagonism causing the anticholinergic triad of urinary retention, constipation, and dry mouth.
**D.** Wrong. Venlafaxine (SNRI) commonly causes hypertension, nausea, and discontinuation syndrome but is not strongly anticholinergic.