Repurposing existing medicines can expedite drug development

The development of new medicines is an expensive and time-consuming process, so pharmaceutical companies need deep pockets and huge resources to see potential new treatments through to marketing authorisation. However, an increasing trend in repurposing existing medicines for new indications can expedite the development process, which benefits patients by making new medicines available sooner than if developed from scratch, and pharmaceutical companies benefit from reduced costs.

The average development time to get a new drug to market is around 10-15 years, and costs a huge 1-2 billion dollars.¹ When originating a new drug from first principles – which is usually the case - the process is complex, starting with target validation and moving on to high-throughput screening of candidate molecules and optimisation of the lead candidate.¹ Only then can the preclinical testing begin to establish efficacy potential and toxicity. Just these initial stages can take more than 5 years and eat up as much as a third of the total budget.¹ If the candidate drug is successful after these stages, it will progress to clinical studies – phases I to III – in human subjects. Unfortunately, only 10-15% of all drugs make it through all these development stages to final approval, highlighting the enormous risks pharmaceutical companies take every time they embark on such projects.¹ However, when a medicine makes it right through to marketing authorisation the rewards for the company can be huge, and patients have a new treatment option which will hopefully improve clinical outcomes.

Possibly because of this fine balance between risk and benefit, there has been a growing trend in the repurposing of existing drugs to treat different conditions for which the original medicine was not indicated. There may be several reasons that a particular drug is selected for trials in a new disease; for example, there may be data from the original clinical trials which suggest an unexpected benefit, or post-marketing reports might highlight a clinical effect unconnected to the condition being treated. Whatever the reason, there is clearly enough of a signal to prompt further investigation.

Sildenafil made the news in the late 1990s as a new on-demand treatment for erectile dysfunction (ED) (made famous by its blue tablet).² It works by inhibiting the enzyme phosphodiesterase type 5 (PDE5) which is involved in controlling smooth muscles. Following sildenafil’s approval by the European Commission (EC) in 1998 for ED, it was found that the lungs of patients with pulmonary arterial hypertension (PAH - a disease that narrows blood vessels in the lungs) have over-expression of the PDE5 gene. This link led to research on the potential for sildenafil to benefit patients with PAH, and subsequently sildenafil was approved for PAH by the EC in 2005.²

In the field of allergy, a drug used to treat asthma - zileuton - is being investigated for its possible role in preventing severe reactions (i.e., anaphylaxis) in people with food allergies. Using an animal model of severe peanut allergy, researchers found that a single oral dose of zileuton an hour before peanut exposure prevented animals from showing signs of anaphylaxis.³ Trials are now underway in humans and could, in the future, provide an important tool in the battle against food allergies.

One might not be too surprised at the repurposing of sildenafil or the potential for zileuton in food allergies, since increasing blood flow is common to the treatment of ED and PAH,² and zileuton has already established its effectiveness in treating a different allergic condition.³ But many medicines are being investigated for their ability to treat very different conditions to those for which they were initially approved. The DPP-4 inhibitor, sitagliptin, for example, is an established oral treatment for type 2 diabetes which is being investigated for potential benefit in preventing recurrent miscarriage.^4,5 Just as unexpected is the potential use of a cough medicine - ambroxol - to help slow down cognitive decline in people with Parkinson's disease dementia.⁶ After taking the drug for 1 year (which is thought to act on an enzyme, beta-glucocerebrosidase, that slows neurodegeneration), patients showed no decline in neuropsychiatric symptoms, whereas those on placebo showed worsening symptoms.⁶ On a similar theme, a treatment for insomnia - lemborexant - may hold promise for preventing Alzheimer’s disease-related brain damage. Preclinical research has found that lemborexant prevented the build-up of abnormal tau proteins in the brains of mice, avoiding the inflammatory brain damage typically seen in dementia.⁷ This work now needs to be repeated in human clinical trials, but the potential is exciting.

Repurposing existing medicines has many advantages for pharmaceutical companies. Not only does it reduce development time and regulatory processes, it also lowers costs.⁶ But ultimately, it is the patients who benefit, so any new approach to drug development that allows for earlier availability should be welcomed.

If you work in drug development or another area of the pharmaceutical industry and you would like help communicating your messages to your target audiences, please do get in touch; we would love the opportunity to partner with you and help you achieve your goals.

References

1. Sun D, Gao W, Hu H, et al. Why 90% of clinical drug development fails and how to improve it? Acta Pharm Sin B. 2022;12(7):3049-3062.

2. Ghofrani HA, Osterloh IH, Grimminger F. Sildenafil: from angina to erectile dysfunction to pulmonary hypertension and beyond. Nat Rev Drug Discov. 2006;5(8):689-702.

3. Hoyt LR, Liu E, Olson EC, et al. Cysteinyl leukotrienes stimulate gut absorption of food allergens to promote anaphylaxis in mice. Science. 2025;389(6760):eadp0240.

4. BBC News. Womb lining test offers miscarriage hope to women. Available at: https://www.bbc.co.uk/news/articles/c39zvjmmwndo (Last accessed August 2025).

5. Muter J, Kong CS, Nebot MT, et al. Stalling of the endometrial decidual reaction determines the recurrence risk of miscarriage. Sci Adv. 2025;11(26):eadv1988.

6. Silveira CRA, Coleman KKL, Borron K, et al. Ambroxol as a Treatment for Parkinson Disease Dementia: A Randomized Clinical Trial. JAMA Neurol. 2025;82(8):797–807.

7. Parhizkar S, Bao X, Chen W, et al. Lemborexant ameliorates tau-mediated sleep loss and neurodegeneration in males in a mouse model of tauopathy. Nat Neurosci. 2025;28(7):1460-1472.