These "cholinesterase inhibitors" include tacrine (Cognex), donepezil (Aricept), rivastigmine (Exelon) and galantamine (Razadyne, formerly called Reminyl).

CNN: Better understanding of dementia leading to more effective therapies

Cholinesterase inhibitors are not useful in dementia caused by Huntington's disease or traumatic brain injury.

CNN: Better understanding of dementia leading to more effective therapies

Donepezil is one of a class of drugs known as cholinesterase inhibitors while memantine is a glutamate moderator.

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Drugs that stop the action of cholinesterase, the enzyme that breaks down acetylcholine, are useful in the treatment of Alzheimer's disease.

CNN: Better understanding of dementia leading to more effective therapies

It's unclear if the results would apply to other cholinesterase inhibitors such as galantamine (Razadyne) or rivastigmine (Exelon), the editorial noted.

CNN: Hard to tell, but drug helps as Alzheimer's progresses

Takeda, another Japanese firm, also has a cholinesterase inhibitor on trial, as do Bayer, of Germany, and Forest Laboratories, an American firm.

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Effects of the traditional Chinese herbal medicine Yi-Gan San for cholinesterase inhibitor-resistant visual hallucinations and neuropsychiatric symptoms in patients with dementia with Lewy bodies.

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"I think the cholinesterase inhibitors have established themselves as the standard of care, " says Roger Lane , clinical program leader for Novartis' entrant, Exelon.

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It is often used in combination with a cholinesterase inhibitor.

CNN: Better understanding of dementia leading to more effective therapies

Aricept, made by Eisai, of Japan, is another cholinesterase inhibitor.

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Surplus acetylcholine is mopped up by an enzyme called cholinesterase.

ECONOMIST: Disposing of dementia | The

Memantine has fewer side effects than the cholinesterase inhibitors.

CNN: Better understanding of dementia leading to more effective therapies

While cholinesterase inhibitors are useful in many early dementias, studies have not shown that treatment of patients with mild cognitive impairment, which is the condition before dementia, prevents or slows progression to dementia.

CNN: Better understanding of dementia leading to more effective therapies

In general, cholinesterase inhibitors have shown some benefit for patients with vascular dementia, those with mixed Alzheimer's and vascular dementia, patients with the disease known as "dementia with Lewy bodies, " and dementia from Parkinson's disease.

CNN: Better understanding of dementia leading to more effective therapies