Characterization of chronic cough patients participating in a phase 2b clinical trial of gefapixant, a P2X3 receptor antagonist

Background: We evaluated clinical characteristics of patients with severe refractory/unexplained chronic cough (RCC/UCC). Methods: RCC/UCC subjects (cough duration ≥1 year, severity VAS >40mm) were randomized to placebo or gefapixant (7.5 mg, 20 mg, or 50 mg) in a 12-week, double-blind, parallel group study (NCT02612610) in RCC (chronic cough unresolved upon treatment of underlying conditions) and UCC (underlying condition could not be identified) subjects (Gibson PG. Chest 2016. 149: 27-44). Prior medications, medical history, and characteristics were recorded at baseline. Results: 253 subjects were randomized (76% female, mean age 60 years, 30% former smokers) with mean (SD) duration of cough of 14.2 (11.1) years. Most subjects were diagnosed with RCC; secondary diagnoses included gastrooesophageal reflux disease (GERD) (56.3%), asthma (29.8%), allergic rhinitis (29.4%), and upper airway cough syndrome (12.3%). The most common prior therapies included steroids (21.4%), antihistamines (15.4%), stomach-acid reducers (15.1%), bronchodilators (14.4%), and cough suppressors (opioids [8.3%] or benzonatate [9.1%]). The most common medical history items at baseline that have been previously been described as complications related to cough (Irwin RS Chest 2006. 129 (1): 55S-58S) included headache (15.1%), hiatus hernia (12.7%), stress urinary incontinence (4.8%), bronchitis (4.4%), and urinary incontinence (2.8%). Conclusions: Large proportions of chronic cough patients in this trial were diagnosed with GERD, asthma, or allergic rhinitis. Despite receiving treatment for these conditions, chronic cough for these subjects had persisted for over a decade.