The Alzheimer's Disease Society has challenged researchers' claims that new drug therapies could effectively pay for themselves by keeping patients out of institutional care.

Executive director Harry Cayton said he was concerned that the conclusion of a new study 'overestimated' the impact drugs would have on costs.

The study of the financial burden of Alzheimer's disease was published this week by a team led by Professor Nick Bosanquet of the health policy unit at Imperial College school of medicine.

Novartis Pharmaceuticals UK Ltd, manufacturer of the drug, Exelon, has backed the report's distribution with a grant.

The report says the annual costs of treating Alzheimer's disease could rise from pounds 5.5bn now to pounds 7.7bn by the year 2021. Previous estimates put the cost of caring for people with the condition at just over pounds 1bn.

Although there is no evidence that the prevalence of the disease is increasing, treatment costs will continue to go up as the population gets older, the report adds.

It says Alzheimer's disease patients are four times more likely to receive institutional care, such as in nursing homes or local authority homes, than the overall age-matched population.

It adds that new drug therapies may reduce the symptoms of the disease to the extent that patients may be prevented or delayed from being admitted to institutional care.

A delay of 3.4 weeks would cover the cost of six months of drug therapy worth pounds 500, the report's authors claim. 'Our estimates suggest that the cost of symptomatic drug therapy may be offset completely in many situations if only a few weeks of institutional care can be avoided through its use.'

But Mr Cayton said: 'The conclusion they draw seems to be optimistic in relation to the potential impact of drugs on costs.'

Although quality of life might improve, it was not clear to what extent new drug therapies would be able to help avoid or delay institutional care, Mr Cayton argued.

The report recommends that symptomatic drug therapies should form part of 'integrated care packages'.

It continues: 'New approaches to care delivery may help to lift some of the burden this disease represents, both in terms of institutional care avoided and in terms of improvements in quality of life for sufferers and their carers.'

Alzheimer's Disease in the United Kingdom: burden of disease and future care. From 0181-940 0648. Free.