Drug repurposing in rare diseases: Myths and reality.

While nearly 8000 rare diseases have been identified, only 5 percent have licensed treatments. As most of these diseases are life threatening, it underscores the urgent need for new drugs. Drug repurposing (also called drug repositioning) consists in identifying new uses for approved or investigational drugs that are outside the scope of the original medical indication. It represents an opportunity for rare diseases and patients with unmet needs. It is an alternative option in drug development and is often presented as being a viable, risk-managed strategy for pharmaceutical companies developing orphan drugs. Drug repurposing is presented as offering various advantages over developing an entirely new drug for a given indication: fewer risks, lower costs and shorter timelines. However, matters are not as simple as this. There are notable successes for drug repurposing. Nevertheless, repurposing does not always succeed. The repurposed drug may fail to demonstrate a benefits-harms balance in clinical trials. Moreover, there are legal and regulatory issues which are specific barriers to drug repurposing and which have to be carefully analyzed before any development of repurposed drugs. The objective of this article is to identify major challenges and opportunities of drug repurposing in rare diseases and to separate fact from fiction.