Efficacy and Safety of Gefapixant (MK-7264) in Adult Participants With Recent Onset Chronic Cough (MK-7264-043)

Inclusion Criteria: * Chest radiograph or CT thorax (within 1 year of Screening/Visit 1 and after the onset of chronic cough) not demonstrating any abnormality considered to be significantly contributing to the chronic cough or any other clinically significant lung disease, in the opinion of the principal investigator or the subinvestigator * Has chronic cough (defined as duration of \>8 weeks after onset of cough symptoms) for \<12 months prior to the screening visit (\<14 months after onset of cough symptoms) * Has a diagnosis of refractory chronic cough or unexplained chronic cough * Female participants are not pregnant, not breastfeeding, not of childbearing potential, or agree to follow contraceptive guidance Exclusion Criteria: * Is a current smoker * Has given up smoking within 12 months of screening * Is a former smoker with a smoking history greater than 20 pack-years (1 pack of 20 cigarettes per day for 20 years) * Has a history of respiratory tract infection or recent change in pulmonary status within 4 weeks of screening * Has a history of chronic bronchitis, defined as cough that produces \>1 tablespoon of phlegm, that occurs every day for at least 3 months in a row * Has a history of malignancy ≤5 years prior to signing informed consent except for adequately treated basal cell or squamous cell skin cancer or cervical cancer * Is a user of recreational or illicit drugs or a recent history (within the last year) of drug or alcohol abuse * Has a history of anaphylaxis or cutaneous adverse drug reaction to sulfonamide-containing drugs * Has a known allergy to gefapixant or its excipients * Has donated or lost ≥1 unit (\~300 mL) of blood within 8 weeks prior to first dose of gefapixant * Has previously received gefapixant * Is currently participating or has participated in an interventional clinical study within 30 days of participating in this current study