A new study has said that the most prescribed drug to treat mild Alzheimer's disease, Aricept (donepezil), has been shown for the first time to help patients with more severe cases too.
The research was funded by the UK Medical Research Council and the Alzheimer's Society, and received donated pills from the pharmaceutical companies Pfizer-Eisa and Lundbeck but drugmakers were not otherwise involved.
Treating patients with advanced Alzheimer's offered "significant functional benefits over the course of 12 months," said the article in the New England Journal of Medicine which included nearly 300 patients.
Doctors often stop prescribing donepezil to patients with more advanced dementia because the drug's benefit is unclear and treatment may appear to have less benefit as the disease progresses.
The randomized clinical trial looked at the effects of donepezil on patients with moderate to severe Alzheimer's who scored between five and 13 on a scale of one to 30, where 30 indicates higher cognitive function.
It found that taking donepezil for 52 weeks resulted in improved scores on mental tests and measures of daily activity compared to those who were assigned to discontinue the drug.
"For the first time, we have robust and compelling evidence that treatment with these drugs can continue to help patients at the later, more severe stages of the disease," said lead author Robert Howard from the Institute of Psychiatry at King's College London.
"We observed that patients who continued taking donepezil were better able to remember, understand, communicate and perform daily tasks for at least a year longer than those who stopped taking the drugs."
Howard added that since donepezil will be available soon in cheaper, generic form, the findings could "greatly increase the numbers of patients in the developed and developing world that we are able to treat."
Some 18 million people around the world suffer from Alzheimer's disease, which is the most common form of dementia.
The World Health Organization has said that of the 35 million people who have Alzheimer's and other forms of dementia worldwide, 58 percent live in low- and middle-income countries. By 2050, that figure is expected to reach 71 percent.
Donepezil is a type of drug known as a cholinesterase inhibitor that helps maintain memory and brain function by preserving a chemical neurotransmitter called acetylcholine, and has been on the market since 1997.
The drug was initially approved on the basis of three to six month clinical trials, but its effects beyond one to two years were uncertain.
"There has been an ongoing debate about the usefulness of continued treatment with currently approved medication as patients' illness progress and they become more impaired cognitively," said neurologist Gayatri Devi, who was not involved in the study.
"This study demonstrates these medications are of benefit in helping to maintain function in patients with Alzheimer's disease over the long-term," added Devi, a physician at Lenox Hill Hospital in New York.
However, an accompanying editorial in the journal by Lon Schneider, a physician at the University of Southern California Keck School of Medicine, warned that questions remain about the drug's true effectiveness.
"Notably, only half the patients who were assigned to continue donepezil in this trial maintained their treatment for the entire one-year study period, suggesting that many patients perceived that continuing the medication was not effective," Schneider wrote.
Often, patients stop taking the drug, citing "a perceived lack of efficacy and adverse effects such as anorexia, weight loss, agitation," as well as slow heartbeat and fainting.
The trial's results may not apply to other cholinesterase inhibitors on the market, and should not imply that the drugs are safe to take indefinitely, Schneider added, calling for more research on the long-term effects.