The primary objective of this study will be to evaluate the efficacy of gefapixant (MK-7264) in reducing cough frequency as measured over a 24-hour period. It is hypothesized that at least one dose of gefapixant is superior to placebo in reducing coughs per hour (over 24 hours) at Week 24.



Eligible Ages
Over 18 Years
Eligible Genders
Accepts Healthy Volunteers

Inclusion Criteria

  • Chest radiograph or computed tomography scan of the thorax (within 5 years 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 sub-investigator
  • Has had chronic cough for at least 1 year with a diagnosis of refractory chronic cough or unexplained chronic cough
  • Is a female who is not pregnant, not breastfeeding, not of childbearing potential, or agrees to follow contraceptive guidance
  • Provides written informed consent and is willing and able to comply with the study protocol (including use of the digital cough recording device and completion of study questionnaires)

Exclusion Criteria

  • Is a current smoker or has given up smoking within 12 months of Screening, or is a former smoker with greater than 20 pack-years
  • Has a history of respiratory tract infection or recent clinically significant change in pulmonary status
  • Has a history of chronic bronchitis
  • Is currently taking an angiotensin converting enzyme inhibitor (ACEI), or has used an ACEI within 3 months of Screening
  • Has an estimated glomerular filtration rate (eGFR) <30 mL/min/1.73 m^2 at Screening OR an eGFR ≥30 mL/min/1.73 m^2 and <50 mL/min/1.73 m^2 at Screening with unstable renal function
  • Has a history of malignancy <=5 years
  • Is a user of recreational or illicit drugs or has had a recent history of drug or alcohol abuse or dependence
  • Has a history of anaphylaxis or cutaneous adverse drug reaction (with or without systemic symptoms) to sulfonamide antibiotics or other sulfonamide-containing drugs
  • Has a known allergy/sensitivity or contraindication to gefapixant
  • Has donated or lost >=1 unit of blood within 8 weeks prior to the first dose of gefapixant
  • Has previously received gefapixant or is currently participating in or has participated in an interventional clinical study

Study Design

Phase 3
Study Type
Intervention Model
Parallel Assignment
Intervention Model Description
Participants with refractory or unexplained chronic cough will be randomized to 1 of 3 treatment groups: gefapixant 45 mg twice daily (BID), gefapixant 15 mg BID, or placebo.
Primary Purpose
Double (Participant, Investigator)

Arm Groups

ArmDescriptionAssigned Intervention
Gefapixant 45 mg BID
Participants will receive a gefapixant 45 mg tablet BID during the main study period (24 weeks) and also during the extension period (28 weeks).
  • Drug: Gefapixant 45 mg BID
    Gefapixant 45 mg tablet to be administered orally BID
    Other names:
    • MK-7264
Gefapixant 15 mg BID
Participants will receive a gefapixant 15 mg tablet BID during the main study period (24 weeks) and also during the extension period (28 weeks).
  • Drug: Gefapixant 15 mg BID
    Gefapixant 15 mg tablet to be administered orally BID
    Other names:
    • MK-7264
Placebo Comparator
Participants will receive a matching placebo tablet BID during the 24-week main study period and during the 28-week extension period.
  • Drug: Placebo
    Placebo tablet administered orally BID

More Details

Active, not recruiting
Merck Sharp & Dohme Corp.

Study Contact

Detailed Description

This study will have a main 24-week treatment period and a 28-week extension period of treatment. Participants at selected sites and countries who complete the main and extension study periods may consent to participate in an observational, 3-month, Off-treatment Durability Study Period.


Study information shown on this site is derived from ClinicalTrials.gov (a public registry operated by the National Institutes of Health). The listing of studies provided is not certain to be all studies for which you might be eligible. Furthermore, study eligibility requirements can be difficult to understand and may change over time, so it is wise to speak with your medical care provider and individual research study teams when making decisions related to participation.