Researchers at Imperial College London have identified a widely used drug that could become a possible new cough treatment.

Coughing is the most common reason for visits to the GP and is often the most unrelenting symptom of many respiratory diseases. Chronic persistent coughing can substantially reduce patients’ quality of life and lead to social isolation and depression. Current treatment options are limited, with some medications sold in pharmacies no more effective than placebos.

The medicine investigated in this new study, theophylline, has long been used as a therapy for asthma and other respiratory diseases such as bronchitis, because of its effect of relaxing the airways. Although prior clinical studies suggested it may work as a cough medicine, it has not been previously recognised for this property and the precise mechanism of action was not known.

The researchers tested theophylline by using capsaicin, the active component of chilli peppers, to induce coughing in guinea pigs and trigger activity in isolated sensory nerve cells. They found that theophylline inhibits the cough reflex in guinea pigs and suppresses the activation of sensory nerve cells.

The research also uncovered a possible biological mechanism through which the medication works. This will allow future research to focus on finding other drugs which target the same mechanism but without the side effect profile of theophylline, which can in some circumstances include stomach pains, vomiting and headaches.

The findings are published in the Journal of Allergy and Clinical Immunology.

Professor Maria Belvisi, head of the respiratory pharmacology group in the National Heart and Lung Institute at Imperial College London, said: “This research highlights a new application for a drug which has been previously overlooked. Since theophylline is an approved drug and readily available, it could become an effective cough treatment for patients with intractable cough throughout the developed and developing world.

“These findings could highlight a previously unrecognised beneficial property of theophylline, and identifying its mechanism of action may lead to the development of a new cough medicine with fewer side effects.” 

The next step in the research is to confirm the findings in a clinical trial.

The research was funded by the Wellcome Trust and the Medical Research Council.

Reference: E. Dubuis et al. 'Theophylline inhibits the cough reflex through a novel mechanism of action.' The Journal of Allergy and Clinical Immunology, 2014. doi:10.1016/j.jaci.2013.11.017