Drug repurposing means use existing medicines in a new way, retargeting them at diseases they were not originally designed to treat. According to the DrugBank database, there are over 4,000 different medicines that have been approved worldwide – a huge potential resource of existing therapies for new disease indications. The DREAM (Drug Repurposing for Effective Alzheimer’s Medicines) study is using health data collected during routine clinical care to identify whether drugs approved for other conditions could be repurposed as potential treatments for Alzheimer’s disease (AD) and dementia. However, drugs such as Viagra and Cialis may not prove useful for treating or preventing these diseases according to their new study, which has just been published in the Brain Communications journal. This study was led by Rishi Desai and Madhav Thambisetty of the US-based NIA Laboratory of Behavioural Neuroscience. Drugs such as Viagra and Cialis are classed as phosphodiesterase-5 (PDE5) inhibitors, which work by relaxing smooth muscle cells in blood vessels. As approved treatments for erectile dysfunction and pulmonary arterial hypertension (PAH), many researchers speculate that they could also help treat diseases such as AD and dementia, which often involve blood vessel dysfunction.
In their recent study, members of the DREAM team compared the incidence of AD and dementia in people with PAH, who were being treated with PDE5 inhibitors sildenafil (known commercially as Viagra) or tadalafil (Cialis). Using Medicare records, DREAM researchers matched 2,888 people with PAH receiving PDE5 inhibitors, with 2,888 people with PAH who were being treated using a different drug. They then analysed whether these individuals were more or less likely to develop AD or dementia over time. Their analyses, which used four different statistical approaches to reduce confounding by comorbidities or other factors, showed that there was no link between taking PDE5 inhibitors and altered risk of AD or dementia. They also performed laboratory tests using cell models of disease, which found no effect of sildenafil or tadalafil on biological processes linked to the development of AD and dementia. Together, these results indicate that drugs such as Viagra and Cialis may not be beneficial to people at risk of AD and dementia.
