Atropine-Induced Anticholinergic Syndrome Following Off-Label Sublingual Administration for Refractory Sialorrhea: A Case Report.

A sublingual atropine ophthalmic solution is increasingly used as an off-label therapy for the symptomatic management of refractory sialorrhea because of its rapid onset of action, ease of administration, and generally favourable safety profile when used at recommended doses. Although generally well-tolerated at therapeutic doses, systemic anticholinergic toxicity may occur following medication administration errors or unintentional overdose. We report the case of a 76-year-old man with recurrent head and neck squamous cell carcinoma receiving palliative systemic therapy who presented with acute hyperactive delirium, severe psychomotor agitation, bilateral mydriasis, diffuse cervicothoracic flushing, tachycardia, and severe hypertension. Careful medication reconciliation revealed inadvertent repeated administration of an unquantified number of sublingual atropine drops by a visually impaired caregiver instead of the prescribed regimen. Alternative infectious, metabolic, and medication-related causes were excluded, and the patient was diagnosed with atropine-induced anticholinergic syndrome. Prompt discontinuation of atropine, supportive care, and intravenous neostigmine resulted in complete clinical recovery within 14 hours. This case highlights the importance of recognising the characteristic anticholinergic toxidrome, performing meticulous medication reconciliation, and considering caregiver-related factors when prescribing off-label therapies that require precise dose administration. Careful assessment of the patient's and caregiver's ability to administer medication safely is essential to prevent avoidable adverse drug events.