SHM Converge Scientific Abstract ePoster Gallery-Prolonged Antimuscarinic Toxicity Due to Comorbid Fluoxetine Overdose

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This case describes a 57-year-old man with depression and prior suicide attempts who was found unresponsive at home with empty bottles of doxepin, amitriptyline, and other unidentified pills. In the MICU, he initially developed hallucinations, agitation, hyperthermia, hyperreflexia, clonus, and autonomic instability, which improved with cyproheptadine and midazolam, leading to an initial working diagnosis of serotonin syndrome.<br /><br />However, on transfer to the floor, he remained febrile, tachycardic, agitated, and hallucinating, but no longer had rigidity or clonus. He had dilated, nonreactive pupils, dry mucous membranes, and suprapubic pain suggestive of urinary retention. These findings supported anticholinergic toxicity rather than ongoing serotonin syndrome. The differential also included alcohol withdrawal, encephalitis, acute metabolic encephalopathy, and infection, but these were less likely given the time course, clinical response, and negative workup.<br /><br />The key conclusion was that the patient had prolonged antimuscarinic toxicity from tricyclic antidepressant overdose, likely worsened by co-ingestion of fluoxetine. Fluoxetine inhibits CYP2D6, the major enzyme responsible for TCA metabolism, which can prolong or intensify anticholinergic effects. The presentation illustrated how fluoxetine can delay clearance of TCAs and complicate toxidrome recognition.<br /><br />The patient improved rapidly after rivastigmine, which served both as a diagnostic aid and reversal agent for severe anticholinergic toxicity. The report emphasizes that hospitalists should recognize classic signs of anticholinergic syndrome and consider comorbid fluoxetine ingestion when toxicity is prolonged or atypical. Management remains supportive, with cardiac monitoring, benzodiazepines, and careful reassessment for mixed overdose syndromes.

Asset Subtitle

Jose Bermea

Meta Tag

Author List Han Gao, John M. Cunningham, Jose Bermea

Category Clinical Vignettes

Concept Anticholinergic Toxicity

Concept Tricyclic Antidepressant Overdose

Concept Serotonin Syndrome

Concept Sympathomimetic Toxicity

Concept Neuroleptic Malignant Syndrome

Distinguished Non-Finalist

Presenter Organization Division of Hospital Medicine. University of Texas Health Science Center at San Antonio, Joe R. And Teresa Lozano Long School of Medicine

Presenting Author Jose Bermea

Track Adult

Keywords

anticholinergic toxicity

tricyclic antidepressant overdose

doxepin

amitriptyline

fluoxetine

serotonin syndrome

CYP2D6 inhibition

rivastigmine

urinary retention

hallucinations

Anticholinergic Toxicity

Tricyclic Antidepressant Overdose

Serotonin Syndrome

Sympathomimetic Toxicity

Neuroleptic Malignant Syndrome