The Real-world Treatment Satisfaction by Gefapixiant in Patients with Refractory Chronic Cough in Terms of Cough Improvement and Taste Disturbance. (The RESTORE Study)

Chronic cough has a high global prevalence, but appears to be poorly recognized. Most patients respond to specific treatments against causes of chronic cough. Meanwhile, cough is refractory to such treatments by approximately 20% of patients and they are regarded as "refractory chronic cough (RCC). Gafapixant is a P2X3 receptor antagonist that has demonstrated the reduction of cough in patients with RCC through the inhibition of ATP transmission to afferent nerves. According to the COUGH-1 and COUGH-2, taste disturbance is the most frequent adverse event by gefapixant, with the incidence of 59.3% in COUGH-1 and 68.9% in COUGH-2, respectively. Although 45 mg of gefapixant is well-tolerated even if taste disturbance has occurred, the impact of taste disturbance on cough-specific QoL remains to be unclear in RCC and UCC. Furthermore, both taste disturbance and the improvement of cough by gefapixant would be associated with treatment satisfaction. Therefore, the investigator would like to evaluate factors related to treatment satisfaction by gefapixant in RCC patients. The investigator hypothesize that taste disturbance will be associated with the improvement of cough specific QoL and treatment satisfaction in RCC patients. Furthermore, the investigator would like to evaluate the association of taste disturbance with cough-specific QoL in the real-world clinical practice. In addition, there are no biomarkers available that can predict the efficacy of the improvement of cough by gefapixant. The investigator will also explore biomarkers that can be helpful in predicting well response to gefapixant in RCC and UCC patients.