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.
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".
surce - Ananova