Chronic cough affects 4-10% of the general population is defined as a cough that has lasted for more than 8 weeks. In many cases, the cough subsides over time and when it persists a careful evaluation of symptoms along with targeted investigations can often clarify a cause of the cough. Treatment of asthma, gastro-oesophageal reflux disease, and upper airways cough syndrome often improves the symptoms. However, a minority of patients with chronic cough have no evidence of any underlying condition and can be considered to have unexplained chronic cough.
Refractory unexplained chronic cough can significantly impact quality of life, relationships and work. It may also cause other health problems due to coughing such as hernias, incontinence and back pain. Unfortunately the cause of chronic cough is poorly understood and no licenced treatments for this condition currently exist. One theory is that chronic cough is a result of impulses erroneously being sent via nerves in the respiratory tract to the brain causing cough.
Gefapixant is a new drug designed to block these impulses and a recent trial (https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(19)30471-0/fulltext) has shown that it may be a promising new treatment for patients with chronic unexplained cough. In the trial, 253 patients were included and had to have an unexplained cough for more than 1 year and a normal chest x-ray. Patients were randomly allocated to receive a placebo or gefapixant at varying doses. The trial found that taking the highest dose of gefapixant (50mg twice daily) for 3 months resulted in a 37% reduction in cough compared to placebo. An important side effect occurred in almost half of the patients taking this dose, most commonly distortion of taste. Further trials of gefapixant are ongoing before it can be used in clinical practice.
Unexplained chronic cough currently has no effective treatments. This recent trial suggests that further development of gefapixant and other drugs targeting the nervous system is warranted for the treatment of chronic cough.