The Use of Drug Repurposing in Rare Disease Research

At Allucent, we have been focusing on trends in rare disease research. We reviewed an article from Nature (click here to read it) and took a closer look at rare disease research as a whole (read it here). From there, we reviewed small molecules (click here), antibody therapy (access it here), protein replacement therapies (available here), oligonucleotide therapies (click here for the article), and gene therapies (read it here).

This article continues that exploration with drug repurposing.

What is Drug Repurposing?

Drug repurposing goes by many different names. It has been called drug repositioning, drug rescue, or therapeutic switching. By whatever name you call it, drug repurposing is effectively taking a drug that has been approved for indication and using it to treat another condition. The idea is that when a drug impacts a particular protein or bodily function, targeting that same mechanism may benefit other diseases or conditions. Pursuing this avenue tends to be less risky – researchers already know that the drug is safe, cheaper – while it still needs to be tested for the new indication, repurposing a drug is less expensive than developing one from scratch, and it is faster. 

There are a few different approaches to drug repurposing. In addition to clinical serendipities, drug repurposing opportunities also come in the form of off-label prescriptions. Some 27% of recognized therapeutic uses have off-label prescriptions associated with them and, according to Pharmacy Times, as many as 20% of all the prescriptions filled in the United States for indications that do not have FDA approval specifically. For instance, Prazosin is approved as a hypertension drug, but it is also used to treat post-traumatic stress disorder (PTSD) associated nightmares. 

Clinical Success in Drug Repurposing and Rare Disease Research

Drug repurposing has a long history of success, especially within the rare diseases industry. A good example is the use of Sildenafil in treating the rare disease pulmonary arterial hypertension. The drug is a small molecule phosphodiesterase 5 inhibitor. It was originally approved for angina. In 1998, it received approval for erectile dysfunction thanks to its positive impact on vascular biology. Then, in 2005, the FDA approved it for pulmonary arterial hypertension. Effectively, there is a similar root issue to these very different conditions so they can be treated with the same drug. 

Repurposing drugs has had such success in rare diseases that there are now several efforts devoted to the concept. The European Union’s E-Rare and the International Rare Diseases Research Consortium (IRDiRC) both focus on identifying opportunities for drug repurposing. The IRDiRC alone is targeting 1,000 new rare disease uses by 2027. There are also several organizations and programs that work to facilitate drug repurposing in general, including The Bridging Interventional Development Gaps (BRiDGs) program at the National Institutes of Health (NIH)’s NCATS (National Center for Advancing Translational Sciences).

Strengths and Limitations of the Platform

Drug repurposing has a lot of potential. Academic institutions and patient advocacy groups are navigating public and private efforts to identify potential candidates – but that doesn’t mean that all of the hurdles to this drug class are automatically removed. For one, efficacy and safety in people with the condition being tested is paramount. Further, there is the issue of comorbidity. Having accompanying diseases or issues can influence efficacy and safety. Finally, even if a drug repurposing opportunity is identified, intellectual property can become a barrier. Some drug producers may not wish to allow access to the compounds they have developed or the high costs of doing so may preclude some people.

Answering the Challenge of Rare Disease Research

Rare disease research involves finding solutions for conditions that may not receive much attention. Repurposing allows researchers to leverage some of the knowledge others have gained from testing treatments of other conditions. The gamble may pay off but researchers need to have greater access to the library of compounds that could demonstrate efficacy in some rare diseases or else the promise of drug repurposing remains largely theoretical.

Please note, this post is the seventh in a series of eight articles centered on trends in rare disease research:

  1. Rare Disease Research
  2. Small Molecules
  3. Antibodies
  4. Protein Replacements
  5. Oligonucleotides
  6. Gene Therapy
  7. Drug Repurposing
  8. The Future of Rare Disease Research

For more information on Allucent’s rare disease experience, visit our website.


  • Pharmacy Times, 10 Surprising Off-Label Uses for Prescription Medications (2016). 
  • Tambuyzer, E., Vandendriessche, B., Austin, C.P. et al. Publisher Correction: Therapies for rare diseases: therapeutic modalities, progress and challenges ahead. Nat Rev Drug Discov (2020).
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