Deterioration in donepezil-induced PR prolongation after a coadministration of memantine in a patient with Alzheimer's disease.

The side effects and interaction of memantine and donepezil hydrochloride when used concomitantly are currently unknown. We encountered a case of a 77-year-old female with Alzheimer's disease in which the concomitant use of memantine exacerbated the prolonged electrocardiogram PR interval which appeared while donepezil hydrochloride was being orally administered. In terms of the cardiac circulation system side effects caused by donepezil hydrochloride and memantine, bradycardia has been reported. However, clinicians should be also aware of PR prolongation associated with the concomitant use of donepezil and memantine.