ACHE and Alzheimer disease: Presently, the drugs approved by the United States Food and Drug Administration (FDA) for the clinical treatment of AD generally fall into two categories, i.e., acetylcholinesterase (AChE) inhibitors, such as tacrine, donepexil, and rivastigmine, and N-methyl-D-aspartate (NMDA) receptor antagonists, such as memantine.