Donepezil-Induced Myoclonus in a Patient With Alzheimer Disease

Objective: To report an uncommon adverse event in an elderly patient related to the cholinesterase inhibitor, donepezil. Case Summary: An 80-year-old Greek woman with Alzheimer disease was admitted to the hospital with a sudden onset of myoclonus in both upper and lower extremities after receiving 30 mg of donepezil daily for 25 days. After 36 hours of donepezil remission, the frequency of the myoclonic jerks was sharply reduced. The patient remains asymptomatic after 6 months of follow-up. Discussion: Our literature search yielded only 2 cases of myoclonus in relation to memantine, which has a different action with donepezil; to our knowledge, this is the first report of generalized myoclonus induced by donepezil overdosing. Based on the Naranjo probability scale it was probable that the patient’s myoclonus was related to donepezil because of clear temporal proximity and lack of alternative explanations. Conclusions: Clinicians should take into consideration therapeutic drug monitoring in the event of a potentially rare serious adverse reaction. Further studies are needed to clarify the possible role of donepezil in the pathophysiology of myoclonus.