The Government's health watchdog faces court action over its decision to deny tens of thousands of patients access to dementia drugs, it was announced today.
Companies involved in the marketing of one of the drugs said they had no option but to seek a judicial review of how the National Institute for Health and Clinical Excellence (Nice) reached its conclusions.
Nice rejected an appeal last month over its guidance that states that sufferers with early or late-stage Alzheimer's disease should not have access to Aricept (donepezil), Reminyl (galantamine) or Exelon (rivastigmine).
Another drug, Ebixa (memantine), is only to be used in clinical studies for people with moderately severe to severe Alzheimer's disease.
Today, Eisai, the licence holder of Aricept, and Pfizer, its co-promotion partner, said that Nice had been informed that the companies intended to apply for a judicial review.
The companies said they believed the decision-making process was "unfair" because Nice had repeatedly refused to "disclose a fully working version of the cost effectiveness model used to determine the value of treatment in patients with mild Alzheimer's disease".
Furthermore, the companies said, many of the conclusions in Nice's final guidance "cannot be supported legally, or are irrational".
The companies said they were calling on Nice to withdraw the current guidance and postpone issuing it to the NHS, which is scheduled for later this month.
It said Nice should "disclose a fully transparent working version of the calculations used in the cost-effectiveness model for independent evaluation and comment".
Furthermore, it should develop new guidance "using both a more accurate cost effectiveness model and data".
Dr Paul Hooper, managing director of Eisai, said: "We are deeply concerned about the way that Nice's decision on treatment recommendations for early Alzheimer's disease was reached.
"A judicial review is now the only option remaining to us to ensure that Nice reconsiders how it arrived at such flawed conclusions.
"These flawed conclusions will have a devastating impact on the lives of thousands of people affected by this terrible disease."
Dr Olivier Brandicourt, managing director of Pfizer UK, said: "Nice has failed to listen to the voices of patients, carers and numerous medical experts.
"By denying consultees the opportunity to check the accuracy of their economic analyses, Nice has left no option but to proceed in this way to ensure that patients with Alzheimer's disease are protected from failures in process."
Neil Hunt, chief executive of the Alzheimer's Society, said it was "great news" that Nice was to face a legal challenge.
He added: "This has been a flawed process from start to finish. Nice holds the fate of thousands of people's lives in its hands and it is only right that it is brought to account.
"The Alzheimer's Society has also been seeking separate legal advice as to whether to launch its own judicial review against this decision in the High Court.
"Nice's decision to deny people in the early and late stages of Alzheimer's disease access to drug treatments is cruel and unethical."
The Society is expecting thousands of people to take part in demonstrations today over the decision.
More than 30 protests will take place across England and Wales, including in London, Manchester, Southampton and Newcastle.
The Alzheimer's Society has collected thousands of signatures and representatives will meet MPs to call for greater flexibility for doctors in prescribing treatments.
More than 125 MPs have already signed an Early Day Motion demanding action to make sure doctors continue prescribing treatments in the best interests of their patients, the charity said.
More than 750,000 people in the UK have dementia, with more than half having Alzheimer's disease.
Dementia affects one in 20 people over the age of 65 and one in five over the age of 80.
Nice chief executive Andrew Dillon said: "We will respond to Eisai's letter and act appropriately in any court proceedings which may follow."
He added: "In the meantime, we will publish our recommendations, both on the best ways of caring for people with all forms of dementia and on the use of drugs for treating Alzheimer's disease, on November 22 2006.
"This will be the first time that health and social care advice has been combined in a single guideline and we believe it is in the interests of those affected by this distressing condition to make it available now."