By Ben Hirschler

LONDON, Nov 27 (Reuters) - Giving Alzheimer's drugs to people with early memory problems does not seem to delay the onset of the disease, researchers said on Tuesday.

Three main drugs -- Aricept, or donepezil; Exelon, or rivastigmine; and Reminyl, or galantamine -- are currently approved for use in mild-to-moderate Alzheimer's disease.

They are also often prescribed on a so-called "off-label" basis to people with pre-dementia.

But doctors are divided over their effectiveness, leading to differing rates of use and bitter arguments over patient access to treatment, notably in Britain where a dispute over their cost-effectiveness has led to legal clashes.

Some experts and patient groups have called for such anti-cholinesterase drugs to be given to people with mild cognitive impairment (MCI) -- a condition where people have memory problems that are more severe than those normally seen in others of their age.

People with MCI are thought to be at high risk of developing Alzheimer's or dementia.

Italian researchers, however, found that in none of six clinical trials they examined did using the drugs significantly reduce the rate of progression from MCI to dementia.

Accurate assessment of the effect of anti-cholinesterase medicines was muddied by the lack of a precise definition for MCI, Roberto Raschetti and colleagues at the National Centre for Epidemiology, Surveillance and Health Promotion in Rome reported in the online journal PLoS Medicine.

Their findings may prompt a rethink among doctors who are currently using anti-cholinesterase drugs off-label in MCI. Off-label use refers to the common practice of prescribing drugs for uses for which they are not officially approved.

In Italy, an estimated 27 percent of patients diagnosed with MCI are given Alzheimer's drugs off-label and Raschetti said it was likely the situation was similar in other countries.

He argued more clinical trials were needed, using a single agreed definition of MCI, before there could be any justification for doctors to use the drugs in pre-dementia cases, especially as the drugs can have harmful side effects.

Aricept is marketed by Japan's Eisai Co Ltd <4523.T> and Pfizer Inc <PFE.N>, while Novartis AG <NOVN.VX> sells Exelon. Reminyl is sold by Shire Plc <SHP.L> and also by Johnson & Johnson <JNJ.N> under the brand name Razadyne.

A row over who should get these drugs ended up in court in London earlier this year after Britain's National Institute for Health and Clinical Excellence said they should not be given to newly diagnosed patients with mild Alzheimer's disease.

Drugmakers claimed the agency's cost-effectiveness calculations were flawed but the court backed the restrictions in a ruling handed down in August. (Editing by Sue Thomas)

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