Two classes of drugs are currently available for Alzheimer's disease, which have been approved by the U.S. FDA: cholinesterase inhibitors and NMDA antagonists.
The first class of drugs are cholinesterase inhibitors, including Aricept (donepezil), Exelon (rivastigmine) and Razadyne (galantamine), which block the breakdown of the neurotransmitter, acetylcholine. Neurotransmitters are essential for communication in the brain propagating messages from one brain cell to another. Clinical trials have shown that these medications result in improved cognitive function, compared to placebo. These drugs are considered relatively safe with some experiencing reversible side effects such as diarrhea, nausea, and/or vomiting. Arcept and Exelon have been approved for mild, moderate, and severe Alzheimer's disease. Razadyne has been approved for mild and moderate Alzheimer's.
The second class of drugs are NMDA (N-methyl-D-aspartate receptor) receptor antagonists, which includes only Namenda (memantine). NMDA receptors are a type of glutamate receptor. These receptors are important in controlling synaptic plasticity and memory formation. In Alzheimer's disease it is thought that these receptors become over excited (over activated) leading to excitotoxicity (the accumulation of toxic species that may cause brain cell damage or death) in the brain. Therefore, memantine works to block the overactivation of this receptor. However, it does not interfere with normal synaptic (the connections between brain cells) activity. Namenda is approved for moderate and severe Alzheimer'se disease and is often used in combination with other drugs. Namenda has been shown to have a small positive effect on cognition, mood and behavior. In general, Namenda is well-tolerated with common adverse side effects including confusion, dizziness, drowsiness, headache, insomnia, agitation, and/or hallucinations.