Despite the increasing prevalence of Alzheimer's disease, the number of potential new drugs being developed is ‘relatively small' and the rate of success of clinical trials in this area is ‘limited', scientists have warned.

Alzheimer's disease affects an estimated 44 million people worldwide and some 35,000 people in Ireland. As the world's population ages, prevalence of the disease is increasing. There is currently no cure and just five drugs are approved for treatment.

According to US scientists, there is ‘an urgent need to find new therapies for Alzheimer's disease'. They set out to assess the development of drugs for the disease. They analysed data from a website that records ongoing clinical trials, focusing on the period 2002 to 2012, and also looked at what is currently in the pipeline.

They found that between 2002 and 2012, 413 Alzheimer drug trials were performed - 124 phase one trials, 206 phase two and 83 phase three trials.

However, the scientists found a ‘very high attrition rate', with an overall success rate of just 0.4%. In other words, 99.6% of the trials failed.

They also found that the number of clinical trials has been declining since the 2008/2009 period.

"Most drugs entering the Alzheimer drug-development pipeline have failed and only one agent has been approved since 2004. Currently, 108 trials of Alzheimer therapies represent 94 unique agents. This is a relatively small number of test compounds. The small number of agents in phase one (22) is particularly concerning, as it suggests that relatively few drugs are entering the Alzheimer drug-development process," the scientists from Nevada said.

They concluded that overall, ‘relatively few' clinical trials centre on the treatment of Alzheimer's disease ‘considering the magnitude of the problem'.

"The success rate for advancing from one phase to another is low, and the number of compounds progressing to regulatory review is among the lowest found in any therapeutic area. An urgent need exists to increase the number of agents entering the pipeline and progressing successfully toward new therapy for patients with Alzheimer's disease," the scientists added.

Details of these findings are published in the journal, Alzheimer's Research & Therapy.

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