Defining Drug Repurposing

There are a number of different definitions of drug repurposing. All of them contain two key elements:

  • taking existing scientific or medical knowledge and technology that is “approved” for human use in one disease or condition; and
  • applying this knowledge and technology to another disease or condition.

The National Center for Advancing Translational Sciences uses the following definition:

“Repurposing generally refers to studying drugs that are already approved to treat one disease or condition to see if they are safe and effective for treating other diseases”.

The process to identify drugs that might have multiple uses can vary. It seems obvious that if two drugs are similar, they might be used to treat the same disease, and if two diseases are similar, they could be treated with the same drug or family of drugs. But drugs can have benefits across for very different conditions.  For example, sildenafil (Viagra) was first designed for angina, and was then found to work in erectile dysfunction and pulmonary arterial hypertension. Sildenafil is now being tested in cancer.

iStock_000008847188_XXXLargeRepurposed drugs may have a good effectiveness record with their primary condition. For example, aspirin was an effective pain reliever before it was used to deter heart attacks. But successful repurposed drugs can come from drugs that have failed in their initial diseases. For example, Thalidomide was designed as a treatment for morning sickness, but it was withdrawn from the market because it caused birth defects.  Later, it was reintroduced as a repurposed drug to effectively treat both leprosy and the cancer multiple myeloma.

Repurposed drug treatments

  • Can cost $250K

0 years
to get drug to market

Clinical trials 1-3 years

Off-label use possible

3 in 10 successful

  • Useful for all diseases

Novel drug treatments

  • Can cost over $1 billion

0 years
to get drug to market

Clinical trials last approximately 6 years

Requires FDA approval

1 in 10,000 success rate

  • Optimal for profitable diseases

How It Works

Drug repurposing is often a collaborative effort requiring multiple stakeholders. After thinking up or observing a possible repurposed use for a drug, researchers must obtain funding from government institutionsphilanthropic organizations, and other sources to pay for  validation studies.  Chemists and engineers may need to modify the drug to help it work better with the new disease, which could involve an entirely different body system.  Once the repurposed drug is properly formulated, proof of concept clinical trials can be carried out on both healthy volunteers and patient to confirm that the drug is both safe and effective. If it meets both of these requirements, results are published so it can either be used immediately by clinicians off label, or it can further tested in a larger clinical trial towards getting regulatory approval.  Both ways can achieve the ultimate goal of repurposing: getting more cures to the patients who most need them.

Innovations From Practice

The potential for a drug repurposing can come from researchers in a lab but it often comes from those on the front-lines. Physicians working with their patients often experiment with different drugs to find the most effective treatments especially when no FDA-approved treatments exist. This Off-label use accounts for approximately 20% of drug prescriptions written by physicians in the US. If a drug is seen to effectively treat symptoms of a condition outside the scope of its traditional purpose, doctors and other healthcare workers will communicate this information to one another and to those who may benefit from it.

The Benefits of Drug Repurposing

It’s Less Risky

It is estimated that roughly 1 in 10,000 new chemical entities that enter the pharmaceutical research & design process actually makes it to market (1). Due to rigorous government standards and the high probability that a drug will have unintended effects in humans, getting a new drug approved is no easy task. Since a repurposed drug has already passed a significant number of toxicity and other tests, its risks are better known and the chance of failure due to adverse side effects is reduced. In fact, the success rate for repurposed drugs was almost 30% in 2012 (2).

It’s Faster

Bringing a brand-new pharmaceutical compound to market takes over a decade from start to finish (3), but patients with terminal cancers, orphan diseases, and other incurable conditions often do not have a decade to spare. Fortunately, studies have shown that approval of an existing drug for a new use can be achieved in only 4 years after a drug is designated to be repurposed (4). By reducing the time commitment for development of a repurposed therapy, repurposing can drive treatments to patient much sooner.  And if the endpoint is off-lable use instead of regulatory approval, drug repurposing can get to patients in 3 years or less.

It’s Cheaper

It is estimated that synthesizing, testing, and bringing a novel drug to market can cost up to $2.6 billion (5). Repurposed drugs bypass much of the early cost needed to bring a drug to market, such as the narrowing down of thousands of  preliminary compounds and years’ worth of preclinical tests on laboratory animals. With a lower price tag, more patients will have access to and be able to afford their repurposed medications. And considering the fact that in 2012 over 50 million Americans did not fill a prescription due to cost, this is very good news for patients in need (6).

It Creates Opportunities to Treat All Diseases

All pharmaceutical companies seek to help patients and secure a profit from drug development. This means that some types of diseases receive might receive less attention from industry, such as:

  • rare diseases that affect small numbers of people;
  • acute diseases, such as infections, where the patients don’t take the drugs for very long; and
  • neglected diseases that may affect large number of people who have no means to pay for treatments.

Repurposing drugs can dramatically lower the costs of drug development so that treatments can be found for these kinds of conditions where new drug discovery costs could not create a reasonable return on investment.

There is a significant need for drug repurposing from the patient viewpoint – over 25 million people suffer from unsolved rare diseases, and over 1 billion people are affected by neglected diseases that debilitate, disfigure or kill (7).

Repurposing can also focus on drugs that have lost their blockbuster status and where a company no longer has exclusive patent rights or controls drug pricing. Once a drug has come off patent and becomes a generic there is little incentive for a pharmaceutical company to explore its potential use for other conditions. Creating new incentives to repurpose generic drugs can deliver affordable treatments to rare disease, acute disease and neglected disease patient populations.

1. PhRMA Innovation Hub. “Drug Discovery and Development: Understanding the R&D Process.” Brochure. Accessed online May 2015. [Link here]
2. Institute of Medicine of the National Academies. “Genomics-Enabled Drug Repurposing and Repositioning: A Workshop.” Roundtable on Translating Genomic-Based Research for Health. Washington, D.C., 24 June 2013. [Link here]
3. Executive Office of the President of the United States, President’s Council of Advisors on Science and Technology. Report to the President on Propelling Innovation in Drug Discovery, Development and Evaluation. September 2012. [Link here]
4. Braun M.M., Farag-El-Massah S., Xu K., and Cote T.R. (2010). Emergence of orphan drugs in the United States: a quantitative assessment of the first 25 years. Nature Reviews Drug Discovery 9: 519-522. [Link here]
5. Mullin, R (2014). “Tufts Study Finds Big Rise in Cost of Drug Development.” Chemical & Engineering News. Web. 20 November 2014. [Link here]
6. Princeton Survey Research Associates International. “2012 Commonwealth Fund Biennial Health Insurance Survey.” 26 April-19 August 2012. [Link here]
7. Drugs for Neglected Diseases Initiative (n.d.). [Link here]