Call it scientific serendipity–scientists testing a drug to treat angina pectoris unexpectedly stumbled upon a remedy for erectile dysfunction. In the 1980s, pharma giant Pfizer began testing a compound called sildenafil to relax the coronary arteries and improve blood flow to the heart. But the clinical trials were not promising, and the drug failed to have the desired cardiovascular impact. Then, some patients participating in the trials reported an unexpected side effect–strong and lasting erections. So began the development of the famous little blue pill called Viagra, and a failed drug development effort turned into a spectacular success.

Viagra opened the door for the development of other erectile dysfunction drugs, and unwittingly created the drug repurposing paradigm–a new, agile approach to testing and expanding the therapeutic arsenal for combatting disease. Drug repurposing consists of finding other uses for existing drugs and molecules beyond their primary indication. Old staples of the drugstore such as aspirin and topiramate (for epilepsy) are already being studied for possible use in treating other conditions.

A typical drug or vaccine development effort takes between 10 and 15 years before regulatory approval is obtained, and it can cost up to US$2.65 billion according to New Uses for Old Drugs (Nuevos usos para viejos medicamentos, CSIC 2021), a recent book by Spanish scientists Nuria E. Campillo, María del Carmen Fernández, and María Mercedes Jiménez. They call the drug development process “an obstacle course.” It’s a race that may start with 10,000 different compounds, but after all the tests and trials to find a safe and effective therapeutic target, only one makes it to the finish line. And sometimes no one finishes the race.

The drugs on the market today all made it to the end of long and costly obstacle courses. But drug repurposing is gaining ground as an alternative development process that offers shorter timeframes and lower costs. Up to 75% of the drugs found in pharmacies today may have new therapeutic uses for 20 new clinical applications beyond the currently approved use, say Campillo and her colleagues.

In an interview with EL PAÍS, Dr. Nuria Campillo, a chemist with the Spanish National Research Council (Consejo Superior de Investigaciones Científicas - CSIC), said that since these drugs have already passed safety and toxicity tests, researchers can forego the preclinical phases. “We can save time and money, and also spare the animals used in testing,” said Campillo. Beatriz Gómez, a scientist with the Rare Diseases Networking Biomedical Research Center in Madrid (Centro de Investigación Biomédica en Red de Enfermedades Raras – CIBERER), said that the drug repurposing approach can potentially achieve “a new indication in three years.” Furthermore, the cost of launching a repurposed drug can be as low as US$318 million, a far cry from the billions it costs to develop a new drug from scratch.