Cholinergic Crisis with Normal Serum Cholinesterase Levels due to Excessive Galantamine Ingestion: A Case Report

Galantamine is a cholinesterase inhibitor employed in Alzheimer's disease management. Cholinesterase inhibitors are associated with potential cholinergic side effects that, when severe, can result in cholinergic crises. Although crises induced by other cholinesterase inhibitors, such as distigmine and rivastigmine, have been reported, cases of galantamine-induced cholinergic crises remain undocumented. This study presents a case of cholinergic crisis triggered by galantamine overdose in an 89-year-old woman weighing 37 kg with Alzheimer's disease history, even though her serum cholinesterase levels were normal. The patient overdosed on 264 mg of galantamine, leading to rapid deterioration, marked by restlessness, tremors, sweating, diarrhea, pharyngeal gurgling, and severe hypoxia. Upon arrival at the emergency department, the patient exhibited pinpoint pupils, compromised airway, and low oxygen saturation, necessitating immediate intubation and transfer to the intensive care unit. After 72 h, the patient successfully recovered and was weaned off mechanical ventilation, maintaining normal serum cholinesterase levels. Animal studies suggest a lethal galantamine threshold of 3 to 6 mg/kg in humans. Unlike other cholinesterase inhibitors that typically reduce serum cholinesterase levels during cholinergic crises, galantamine appears to selectively inhibit acetylcholinesterase, possibly sparing butyrylcholinesterase. This selectivity may explain the normal serum cholinesterase levels.