although this antihistamine drug was once thought to be the “dark-horse” of Alzheimer’s medications. At present, there are five drugs used in the treatment of AD: (1) the cholinesterase inhibitors: donepezil, galantamine, rivastigmine and tacrine; and (2) the glutamate receptor antagonist: memantine. All have been approved in the United States for treatment of AD, although tacrine is now rarely used because of hepatotoxicity.