From Therapy to Toxicity: Anticholinergic Syndrome After Standard-Dose Atropine

Atropine, is an antimuscarinic agent used for symptomatic bradycardia and an antidote for muscarinic toxidrome. The standard treatment protocol involves administering doses of 0.5-1 mg every 3–5 minutes until the desired heart rate is achieved, with a maximum dose of 3 mg. The common side effects include dry mouth, blurred vision, photophobia, and tachycardia. While individual tolerance varies, disturbance of speech, ataxia, disorientation, hallucinations, and delirium are generally not observed at doses exceeding 5 mg. We report a case of a patient treated with standard-dose atropine, and who developed tanticholinergic syndrome without overdose. A 57-year-old female presented to the emergency department with chest tightness, nausea, and vomiting. Initial electrocardiography demonstrated junctional bradycardia. She received standard-dose intravenous atropine. Shortly after atropine administration, her rhythm converted to junctional tachycardia. Approximately two hours later, she developed acute confusion, disorientation, mydriasis, dry mucosa, and orobuccal movements. Based on the symptoms, a diagnosis of anticholinergic syndrome likely induced by atropine was considered. Neuroimaging and laboratory investigations excluded metabolic, infectious, and intracranial causes. The patient was managed conservatively with intravenous fluids and close monitoring. Her symptoms resolved completely within 12 hours. Emergency physicians should recognize that anticholinergic syndrome may develop even after standard-dose atropine administration. Early identification and supportive management are essential, and clinicians should remain aware of possible idiosyncratic reactions.