Drug repurposing is the strategy of using existing drugs for new uses. It can involve a drug at any stage in its development or commercialisation cycle, and offers substantially enhanced productivity for pharmaceutical R&D. In particular, it offers much reduced discovery times, reduced risk of developmental failure, and reduced cost and time of development. Historically, many examples of repurposing arose from serendipitous clinical findings; but drug repurposing may also arise from literature based methods; a deliberate screening exercise or computational techniques.
It has been estimated that up to 90% of compounds currently in therapeutic use or clinical development may have important, unexplored alternative uses. Repurposing an existing drug can offer substantial efficiency to pharmaceutical R&D, avoiding time-consuming preclinical development, and entry into clinical trials for a fraction of the cost and time incurred with a new chemical entity.