Clinical data supporting the efficacy of Pfizer and Eisai’s Aricept in severe forms of Alzheimer’s disease have been published by The Lancet, supporting ongoing efforts by the companies to extend the approved indications of the drug.

Aricept is already cleared to treat mild-to-moderate forms of Alzheimer’s, but Pfizer and Eisai have had trouble persuading regulatory authorities of the product’s value in more severely-affected patients.

The study, which appears as an early online publication on The Lancet’s website, found that donepezil produced a significant improvement in cognition and memory, as well as a slower decline in activities of daily living such as bathing and grooming, compared to placebo.

The lead author of the study, Dr Bengt Winblad, said the results were significant because they suggest that donepezil can reverse and slow deterioration in patients with Alzheimer’s who are in nursing homes, without increasing the length of time they have the disease.

Eisai and Pfizer had an application to market Aricept for severe Alzheimer’s turned down by the US Food and Drug Administration (FDA) last October, after the agency said the file had formatting deficiencies.

The companies have since re-filed the dossier, and hope approval would help maintain Aricept’s sales momentum - Pfizer reported sales of the drug of $346 million last year, a rise of 12% - and also allow it to also make inroads in territory current held by Forest Laboratories' Namenda (memantine), currently the only drug approved to treat severe Alzheimer’s.

Meanwhile, the results will give ammunition to campaigners in the UK, who are battling to make sure the National Health Service continues to fund treatment of mild-to-moderate Alzheimer’s patients with Aricept and other cholinesterase inhibitors. Their cost-effectiveness is currently under review by the UK’s National Institute for Health and Clinical Excellence (NICE).