97 new drugs are currently in development for patients with Alzheimer's disease and other dementias, including 83 for Alzheimer's, 12 for cognition disorders and two for dementias, according to a new US industry report.

However, between 1998 and 2011, 101 such treatments failed to reach patients, and only three medicines were approved to treat symptoms of the disease, representing a 34:1 ratio of setbacks, says the report, which is published by the Pharmaceutical Research and Manufacturers of America (PhRMA).

Of the 101 medicines which have become "inactive" and not received regulatory approval since 1998, 83 have been definitely discontinued, while the others have been "suspended," ie, halted for the foreseeable future, or have "no development reported," meaning no evidence of continued research in the past 18-24 months, says PhRMA. The chance of reactivation of "inactive" projects is very small, it adds.

Since 2003, when the most recent Alzheimer's drug was approved, there have been 66 unsuccessful projects, and recent years have yielded particularly high numbers of halted projects, with an average of 10 per year in 2006-11 compared with five per year during 2000-5, the study shows.

"Setbacks in Alzheimer's research are disappointing to many, including the scientists carrying out the studies, but these unsuccessful attempts are critical stepping-stones to advancing our understanding of this extremely complex disease," commented John J Castellani, chief executive of PhRMA.

"The reality is that so-called failures in the development of new drugs for Alzheimer's are helping redirect research - providing new information that allows science to move forward," he added.

The potential new treatments now in R&D - either in clinical trials or under review by the US Food and Drug Administration (FDA) include: - an intranasal medicine that is able to penetrate the blood-brain barrier for mild cognitive impairment, a precursor to Alzheimer's disease; - a gene therapy for the treatment of Alzheimer's; and - a synthetic vaccine that induces antibody production without creating a systemic immune response.

The industry report also discusses the scope and economic burden of Alzheimer's on the US. 5.4 million people are currently affected by the disease, and it accounts for $200 billion a year in direct medical costs, due in part to the cost of nursing home care. The indirect costs are at least as high, with the number of family, friends and caregivers of Alzheimer's patients reaching 15. 2 million in 2011, providing paid care valued at more than $200 billion, according to the Alzheimer's Association.

Moreover, the number of people in the US with Alzheimer's is projected to grow every year to reach a total of 13.5 million patients by 2050. On this trajectory, the direct cost of the disease in people aged over 65 could balloon to $1 trillion a year by 2050, in today's dollars, with a total of $20 trillion in medical costs in the next 40 years, the Association adds.

However, the PhRMA report also says that a new treatment that delays the onset of disease by five years would reduce the number of people with Alzheimer's by nearly half and reduce their cost of care by $447 billion a year by 2050.

And a treatment that slows the progression of Alzheimer's by five years would reduce the expected number of people in the severe stage of the disease by over 65% and save $197 billion a year by 2050, it adds.