Table 1.  .

The main difference between Traditional Drug Discovery System and Drug Repurposing [6–13]

TRADITIONAL DRUG DISCOVERY	DRUG REPURPOSING
Include 5 stages:   • Discovery and preclinical   • Safety review   • Clinical research   • FDA review   • FDA post-market safety monitoring	Include 4 stages:     • Compound identification     • Compound acquisition     • Development     • FDA post-market safety monitoring
Generally, more time consuming	Less time consuming
High investment or cost	Lesser investment compared to traditional drug discovery
More risk of failure	Less risk of failure
Clinical efficacy and safety profile should be evaluated	Clinical efficacy and safety profiles already exist

Repurposing drugs have a significant advantage in decreasing the development cost and time to market over standard discovery. Data like pharmacokinetics, toxicology, and safety data from the standard discovery process [14–16].