Uncommon Extrapyramidal Reaction to Ondansetron

Area of Science:

• Oncology
• Neurology
• Pharmacology

Background:

• Chemotherapy for stage IV small cell lung cancer often requires antiemetic premedication.
• Ondansetron and dexamethasone are commonly used for nausea and vomiting prophylaxis.

Observation:

• A patient receiving chemotherapy experienced transient neurological deficits, including altered mental status and right-sided weakness, after ondansetron administration.
• A second episode with anisocoria, facial paresis, and dysarthria occurred, initially suspected as SIADH but rapidly resolved with biperiden.
• These events mimicked cerebrovascular accidents despite negative brain imaging.

Findings:

• The neurological symptoms were strongly associated with ondansetron administration, suggesting an adverse drug reaction.
• Hyponatremia was noted, but rapid symptom reversal with biperiden pointed towards an ondansetron-induced anticholinergic effect or other neurotoxicity.
• Discontinuation of ondansetron and metoclopramide resolved the symptoms and prevented recurrence.

Implications:

• Clinicians must consider ondansetron's potential for neurological adverse effects that can mimic stroke.
• Thorough medication review and differential diagnosis are essential in complex cancer patient presentations.
• Awareness of ondansetron's neurotoxic potential can prevent misdiagnosis and ensure appropriate management.