A recommendation by the body responsible for providing guidance on NHS drugs is to be challenged in court for the first time.
Two drugs companies, Eisai and Pfizer, are applying to the High Court for a judicial review into a decision made by the National Institute for Health and Clinical Excellence (Nice) regarding medication for Alzheimer's disease.
Nice recently recommended that certain treatments, including donepezil, rivastigmine and galantamine, should not be made available for sufferers of mild, recently-diagnosed Alzheimer's disease on the NHS.
The drugs could improve the lives of sufferers for as little as £2.50 a day, campaigners say, but patients will now be forced to seek private treatment or receive alternative medication on the NHS.
"We are deeply concerned about the way that Nice's decision on treatment recommendations for early Alzheimer's disease was reached," said Paul Hooper, the managing director of Eisai.
"These flawed conclusions will have a devastating impact on the lives of thousands of people affected by this terrible disease."
Nice has confirmed that it will act appropriately in any court proceedings that may take place.