Discovering new treatments for Alzheimer's disease by repurposing approved medications.

Alzheimer's disease (AD) is the most common cause of dementia and a major cause of morbidity and mortality. The greatest risk factor for AD is age and as many countries are experiencing an aging population, the expected rise in AD threatens to have serious medical and socioeconomic impact in the coming decades. The only approved medications for AD are symptomatic and there are no currently available disease modifying treatments. Hence, a disease modifying treatment is desperately needed for AD not only for proper care and management of affected patients, but also to reduce society's socioeconomic burden. Developing novel compounds for any indication is a time, effort, and money consuming endeavor and most treatments never make it to market. Other research and development strategies are needed, especially for the treatment of AD. We provide a review of the current literature in assessing possibilities of repurposing medications currently used for non-AD indications. Many different compounds from many different pharmacological classes have already been studied in an AD context. We provide a "pragmatic drug repurposing score" for each of these compounds based on type of studies conducted, number of possible mechanisms of action, efficacy in AD and other neurodegenerative disease studies, tolerability profile, and their ability to cross the blood brain barrier. The current data suggest several compounds worthy of further study as treatments for AD. Compounds with the highest scores include lithium, minocycline, exenatide, valproic acid, methylene blue, and nicotine.