There are currently five medications that are FDA-approved to help people with Alzheimer's disease. None of these can cure or prevent Alzheimer's disease, but they may help alleviate some symptoms and slow disease progression. There are two main classes of Alzheimer's disease medications---the acetylcholinesterase inhibitors (AChEIs) and the NMDA-receptor antagonist memantine---both named for their actions in the brain.
Acetylcholinesterase Inhibitors (AChEIs)
In Alzheimer's disease brain cells known as neurons are damaged or destroyed. Neurons contain chemicals called neurotransmitters, and one of the main ones affected is acetylcholine (ACh). ACh-containing neurons are found in the areas of the brain involved in learning and memory; and some of the main symptoms of Alzheimer's disease are caused when there is not enough ACh to enable these brain areas to function properly. ACh is broken down by an enzyme called acetylcholinesterase, thus the acetylcholinesterase inhibitors (AChEIs) work by stopping the action of this enzyme, so increasing the amount of ACh available.
The current AChEIs are donepezil, galamantine, rivastigmine and tacrine. Tacrine is rarely used due to adverse side-effects and a complicated dosing regimen. The other AChEIs have slightly different mechanisms of action and slightly different side-effects. Acetylcholine also has actions in other parts of the body. General side effects of AChEIs can include nausea, vomiting, decreased appetite, muscle cramps and bradycardia (slow heart-beat).
Donepezil (Aricept)
Donepezil is the only AChEI recommended for people in the severe stages of Alzheimer's disease. It may improve cognitive measures, such as memory and attention, and 'activities of daily living,' such as being able to dress and feed oneself. One of the side-effects specific to donepezil is hallucinations in some patients.
Galantamine (Razadyne)
As well as being an AChEI, galantamine can also affect the release of a number of other neurotransmitters. These actions can boost attention and address behavioral difficulties. The most major side-effect of galantamine is gastrointestinal problems and weight loss, however these are less acute when it is only taken once a day.
Rivastigmine (Exelon)
Rivastigmine inhibits acetylcholinesterase and another enzyme called butyrylcholinesterase (BuChE). Although this can further boost ACh levels, BuChE inhibition can lead to increased gastrointestinal side effects. Use of a rivastigmine patch may bypass these problems.
Memantine (Namenda)
Memantine has an entirely different mechanism of action than the AChEIs. Some of the neuronal damage in Alzheimer's disease is due to increased actions of another neurotransmitter called glutamate. Memantine works by decreasing the ability of glutamate to produce harmful signals, but does not stop them completely, so glutamate can still function as it should. Memantine may slow the progression of Alzheimer's disease symptoms and also help with problems such as aggression and delusions. Side-effects may include gastrointestinal problems as well as agitation.
As memantine and donepezil work on different neurotransmitters they can be used together, which is useful for some people.
References
- "American Journal of Psychiatry"; American Psychiatric Association Practice Guideline for the Treatment of Patients with Alzheimer's Disease and Other Dementias. Second Edition; APA Work Group on Alzheimer's Disease and Other Dementias; Dec 2007
- "Annals of Internal Medicine"; Current Pharmacologic Treatment of Dementia: A Clinical Practice Guideline from the American College of Physicians and the American Academy of Family Physicians. Amir Qaseem et al; Mar 2008
- "Dementia and Geriatric Cognitive Disorders"; Treatment Options in Alzheimer's Disease: Maximizing Benefit, Managing Expectations; Martin Farlow, Michael Miller, Vojislav Pejovic; April 2008
