Researchers assessing Alzheimer’s disease clinical trials from 2002 to 2012 have noted that a depressingly high number of them - 99.6% - aimed at preventing, curing or improving symptoms of the disease failed or were discontinued.

The study, published in the journal Alzheimer’s Research and Therapy, was conducted by the Cleveland Clinic Lou Ruvo Centre for Brain Health and the Touro University Nevada College of Osteopathic Medicine. The researchers sourced to compile a database of all AD trials over the aforementioned decade - 244 compounds assessed in 413 studies.

Of the 83 Phase III trials (and excluding the 14 compounds presently in late-stage development), only one has been approved, Lundback’s Ebixa (memantine) in 2004, which can help with symptoms. The overall success rate for approval is therefore just 0.4%.

The authors of the study note that the current AD pipeline is “relatively modest, given the enormous challenge posed by this disease”, saying that the disease is more expensive to the US economy than cardiovascular disease or cancer. Currently, 108 trials for AD therapies are being conducted, compared with 1,438 for oncology agents and the success rate of development of oncology compounds is 19%.

“Similar successes are needed to spur AD drug development,” they argue, pointing to the small number of agents in Phase 1 (22 at the moment), which is “particularly concerning”. The researchers add that the pipeline is dependent on “a complex drug-development ecosystem” of academia, funding agencies, regulators, venture capital and philanthropy, among others, as well as pharma and biotech firms.

Commenting on the analysis, Simon Ridley, head of research at Alzheimer’s Research UK, said that “there is a danger that the high failure rates of trials in the past will discourage pharmaceutical companies from investing in dementia research. We need to use this data to understand the reasons behind the discontinuation of these trials and address those issues”.

He added that drugmakers “need to commit to continued investment in drug development and clinical trials in order to achieve a breakthrough”.