Which cholinesterase inhibitor is NOT among the commonly used medications to treat dementia?

Memantine (Namenda) is not classified as a cholinesterase inhibitor, which is why it is the correct answer. Instead, memantine is an N-methyl-D-aspartate (NMDA) receptor antagonist that is used to treat moderate to severe Alzheimer's disease. It works by regulating glutamate activity, a neurotransmitter involved in learning and memory, and is believed to help prevent excitotoxicity, which can contribute to neuronal death in dementia.

In contrast, the other medications listed—donepezil, rivastigmine, and galantamine—are all cholinesterase inhibitors. These drugs are commonly prescribed to enhance cholinergic function by inhibiting the breakdown of acetylcholine, a neurotransmitter that is often deficient in patients with Alzheimer’s disease and other dementias. By increasing the levels of acetylcholine in the brain, these medications may help improve cognitive function and slow the progression of symptoms in patients with dementia.