Drug repurposing, also called drug rediscovery or drug repositioning, referred to rediscovering a new indication for an existing drug. One of the most famous examples is sildenafil that was intended to treat angina pectoris but to treat erectile dysfunction instead. Other examples include minoxidil, a drug intended to treat ulcer but to treat hypertension and alopecia finally. Thalidomide, which was launched as a cure for sickness of pregnant in 1950s, was approved for the treatment of multiple myeloma in 2006. Thioguanine, originally developed for leukemia, was repurposed as a rescue immunosuppressive drug for the treatment of patients with inflammatory bowel disease (IBD) in 2001.

Advantages of drug rediscovery:

1)        less time-consuming and expensive;

2)        reduced risk of unexpected side effects;

Obstacles of drug repurposing: Rediscovered drugs are regularly prescribed off-label, thus unlicensed.

Drawbacks of drug repurposing: Lack of interest of pharmaceutical company in drugs with expired patent despite some ways of extending market exclusivity period in EU and America of protected drugs.

Suggestions for drug purposing:

1)        A drug regulatory reform and marketing authorization for rediscovered drugs is needed, including governmental regulation, to prevent excessive drug pricing by pharmaceutical companies.

2)        Prolong market exclusive period of 3 years.

3)        a standardized protocol for the rediscovery of generic drugs should be initiated to aid this procedure.

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https://www.sciencedirect.com/science/article/pii/S1359644617301885