Adults 18 to 80, any sex, with Refractory Chronic Cough. Patients with the condition only — healthy volunteers not accepted.
Results — posted to ClinicalTrials.gov
Per-arm endpoint measurements with 95% confidence intervals where reported. Source: trial results section.
Cough Reflex Sensitivity to Capsaicin in Participants Who Received Gefapixant 100 mg and Placebo (Period 1 & Period 2 Combined)Primary· Average of 1, 3, and 5 hours post-dose
The concentration of capsaicin inducing at least 2 coughs (C2) and at least 5 coughs (C5) was assessed at 1, 3, and 5 hours post-dose in healthy and chronic cough participants. The concentrations of capsaicin for cough challenge were 0.3 micromoles (µM), 1 µM, 3 µM, 10 µM, 30 µM, 100 µM, 300 µM, and 1000 µM. The Measure Type is least-squares mean in natural log scale. The challenge agent was prepared by dilution of capsaicin with saline, and was administered by inhalation. A mixed effects model used natural log-transformed values for the lowest concentrations of inhaled solution required to ev
C2 Response to Capsaicin (Periods 1 & 2)
Group
Value
95% CI
Gefapixant 100 mg/Healthy
3.05
2.6 – 3.5
Placebo/Healthy
3.04
2.6 – 3.5
Gefapixant 100 mg/Chronic Cough
1.72
1.3 – 2.1
Placebo/Chronic Cough
1.41
1.0 – 1.8
C5 Response to Capsaicin (Periods 1 & 2)
Group
Value
95% CI
Gefapixant 100 mg/Healthy
4.46
3.9 – 5.0
Placebo/Healthy
4.68
4.1 – 5.3
Gefapixant 100 mg/Chronic Cough
2.31
1.9 – 2.8
Placebo/Chronic Cough
2.05
1.6 – 2.5
Cough Reflex Sensitivity to Citric Acid in Participants Who Received Gefapixant 100 mg and Placebo (Period 1 & Period 2 Combined)Primary· Average of 1, 3, and 5 hours post-dose
The concentration of citric acid inducing at least 2 coughs (C2) and at least 5 coughs (C5) was assessed at 1, 3, and 5 hours post-dose in healthy and chronic cough participants. The concentrations of citric acid for cough challenge were 1 millimoles (mM), 3 mM, 10 mM, 30 mM, 100 mM, 300 mM, 1 M, and 3 M. The Measure Type is least-squares mean in natural log scale. The challenge agent was prepared by dilution of citric acid with saline, and was administered by inhalation. A mixed effects model used natural log-transformed values for the lowest concentrations of inhaled solution required to evo
C2 Response to Citric Acid (Periods 1 & 2)
Group
Value
95% CI
Gefapixant 100 mg/Healthy
6.16
5.6 – 6.8
Placebo/Healthy
5.61
5.0 – 6.2
Gefapixant 100 mg/Chronic Cough
4.07
3.6 – 4.6
Placebo/Chronic Cough
3.84
3.3 – 4.3
C5 Response to Citric Acid (Periods 1 & 2)
Group
Value
95% CI
Gefapixant 100 mg/Healthy
7.12
6.4 – 7.8
Placebo/Healthy
6.82
6.1 – 7.6
Gefapixant 100 mg/Chronic Cough
4.74
4.2 – 5.2
Placebo/Chronic Cough
4.46
4.0 – 5.0
Cough Reflex Sensitivity to ATP in Participants Who Received Gefapixant 100 mg and Placebo (Period 1 & Period 2 Combined)Primary· Average of 1, 3, and 5 hours post-dose
The concentration of ATP inducing at least 2 coughs (C2) and at least 5 coughs (C5) was assessed at 1, 3, and 5 hours post-dose in healthy and chronic cough participants. The concentrations of ATP for cough challenge were 0.1 mM, 0.3 mM, 1 mM, 3 mM, 10 mM, 30 mM, 100 mM, and 300 mM. The Measure Type is least-squares mean in natural log scale. The challenge agent was prepared by dilution of ATP with saline, and was administered by inhalation. A mixed effects model used natural log-transformed values for the lowest concentrations of inhaled solution required to evoke at least 2 (C2) or at least
C2 Response to ATP (Periods 1 & 2)
Group
Value
95% CI
Gefapixant 100 mg/Healthy
4.79
4.0 – 5.6
Placebo/Healthy
3.90
3.1 – 4.7
Gefapixant 100 mg/Chronic Cough
2.90
2.3 – 3.5
Placebo/Chronic Cough
1.36
0.8 – 2.0
C5 Response to ATP (Periods 1 & 2)
Group
Value
95% CI
Gefapixant 100 mg/Healthy
5.61
5.3 – 5.9
Placebo/Healthy
4.73
4.3 – 5.1
Gefapixant 100 mg/Chronic Cough
3.52
2.9 – 4.2
Placebo/Chronic Cough
2.22
1.6 – 2.9
Cough Reflex Sensitivity to Distilled Water in Participants Who Received Gefapixant 100 mg and Placebo (Period 1 & Period 2 Combined)Primary· Average of 1, 3, and 5 hours post-dose
The concentration of distilled water inducing at least 2 coughs (C2) and at least 5 coughs (C5) was assessed at 1, 3, and 5 hours post-dose in healthy and chronic cough participants. The concentrations of distilled water for cough challenge were 20%, 40%, 60%, 80%, and 100%. The Measure Type is least-squares mean in natural log scale. The number of coughs generated in 1 minute of exposure was recorded. The challenge agent was prepared by dilution of distilled water with saline, and was administered by inhalation. A mixed effects model used natural log-transformed values for the lowest concentr
C2 Response to Distilled Water (Periods 1 & 2)
Group
Value
95% CI
Gefapixant 100 mg/Healthy
4.72
4.6 – 4.8
Placebo/Healthy
4.34
4.2 – 4.4
Gefapixant 100 mg/Chronic Cough
4.42
4.3 – 4.5
Placebo/Chronic Cough
4.12
4.0 – 4.2
C5 Response to Distilled Water (Periods 1 & 2)
Group
Value
95% CI
Gefapixant 100 mg/Healthy
4.85
4.6 – 5.1
Placebo/Healthy
4.61
4.4 – 4.8
Gefapixant 100 mg/Chronic Cough
4.51
4.4 – 4.6
Placebo/Chronic Cough
4.24
4.1 – 4.4
Change From Baseline in Cough Severity Visual Analogue Scale (VAS) After Cough Challenge Testing in Participants Who Received Gefapixant 100 mg and Placebo (Chronic Cough Participants Only)Secondary· Baseline and one hour after the final cough challenge on treatment days
Chronic cough participants completed a visual analogue scale (VAS) to record cough severity, prior to dosing on the treatment day in each treatment period, and one hour after the final cough challenge on the treatment days. This was a 100mm VAS of cough severity from 'No Cough' (0) up to 'Worst Cough' (100). Participants were instructed to draw a line on the scale to indicate how severe they felt their cough was during the previous 1 hour on the treatment days. A negative change from Baseline was considered to indicate improvement in cough severity.
Group
Value
95% CI
Gefapixant 100 mg/Chronic Cough
-26.2
-36.2 – -16.2
Placebo/Chronic Cough
-8.2
-18.7 – 2.2
Change From Baseline in Urge to Cough VAS After Cough Challenge Testing in Participants Who Received Gefapixant 100 mg and Placebo (Chronic Cough Participants Only)Secondary· Baseline and one hour after final cough challenge on treatment days
Chronic cough participants completed a VAS to record the severity of their urge to cough, prior to dosing on the treatment day in each treatment period, and one hour after the final cough challenge on the treatment days. Participants marked the 100mm VAS at the extremes as 'No urge-to-cough' (0) and 'Worst urge-to-cough' (100). Participants were instructed to draw a single vertical line on the scale to indicate how severe their urge to cough was during the previous 1 hour on the treatment days. A negative change from Baseline was considered to indicate improvement in urge to cough.
Group
Value
95% CI
Gefapixant 100 mg/Chronic Cough
-29.8
-38.9 – -20.7
Placebo/Chronic Cough
-11.7
-20.9 – -2.6
Change From Baseline in Cough Frequency After Cough Challenge Testing in Participants Who Received Gefapixant 100 mg and Placebo (Chronic Cough Participants Only)Secondary· Baseline and for 24 hours after cough challenge on treatment days
An ambulatory cough recording device recorded all sounds chronic cough participants made during cough monitoring to measure the change from baseline in objective cough frequency on the treatment days. A negative change from Baseline was considered to indicate improvement in cough frequency
Group
Value
95% CI
Gefapixant 100 mg/Chronic Cough
-7.7
-10.1 – -5.3
Placebo/Chronic Cough
-4.1
-6.5 – -1.7
Percentage of Participants Who Experienced One or More Adverse Events During Study Treatment and Follow upSecondary· Up to Day 18
A secondary endpoint of the trial was the percentage of participants receiving gefapixant 100 mg and placebo who had at least 1 adverse event (AE) over 4 days of treatment (including washout periods) in addition to 14 days (+3 days) until a post-treatment follow-up visit. An AE is defined as any untoward medical occurrence in a participant administered study drug and which does not necessarily have to have a causal relationship with this treatment. Any worsening of a preexisting condition that is temporally associated with the use of the study drug is also an AE. The percentage of participants
Group
Value
95% CI
Gefapixant 100 mg/Healthy
100.0
Placebo/Healthy
50.0
Gefapixant 100 mg/Chronic Cough
95.8
Placebo/Chronic Cough
33.3
Percentage of Participants Who Discontinued From the Study Due to an Adverse EventSecondary· Up to Day 4
A secondary endpoint of the trial was the percentage of participants receiving gefapixant 100 mg and placebo who discontinued from the study due to an AE. The percentage of participants who discontinued from the study due to an AE was assessed for days 1-4.
Group
Value
95% CI
Gefapixant 100 mg/Healthy
0
Placebo/Healthy
0
Gefapixant 100 mg/Chronic Cough
0
Placebo/Chronic Cough
0
Adverse events — posted to ClinicalTrials.gov
Time frame: Up to Day 18.
Reporting threshold: 5%.
Adverse-event reports describe events observed during the trial — not all are caused by the drug.
The primary objective of this study was to assess the effect of a single dose of gefapixant 100 mg on cough reflex sensitivity to various challenge agents (capsaicin, citric acid, adenosine triphosphate \[ATP\], and distilled water) in healthy and chronic cough participants.
Publications & conference data
5 peer-reviewed publications reference this trial (live from Europe PMC):
NCT05600777 — A 24-Week Study of the Efficacy and Safety of BLU-5937 in Adults With Refractory Chronic Cough
· Phase 3
· active not recruiting
NCT05599191 — A 52-Week Study of the Efficacy and Safety of BLU-5937 in Adults With Refractory Chronic Cough
· Phase 3
· active not recruiting
Other Afferent Pharmaceuticals, Inc., a subsidiary of Merck & Co., Inc. (Rahway, New Jersey USA) trials
Trials by the same sponsor.
NCT02790840 — A Multiple-Dose Pharmacokinetics Study of Three Gefapixant (AF-219/MK-7264) Formulations
· Phase 1
· completed
NCT02612623 — An 8-Week Refractory Chronic Cough Study (MK-7264-021)
· Phase 2
· completed
NCT02612610 — A 12-Week Study in Participants With Refractory Chronic Cough (MK-7264-012)
· Phase 2
· completed
NCT02502097 — A Study of Gefapixant (AF-219/MK-7264) in Participants With Idiopathic Pulmonary Fibrosis (IPF) With Persistent Cough (M
· Phase 2
· completed
NCT02477709 — A Study to Assess the Tolerability of a Single Dose of Gefapixant (AF-219/MK-7264) in Subjects With Idiopathic Pulmonary
· Phase 2
· completed
Publications: Europe PMC API search by NCT ID, retrieved 10 June 2026
Drug + disease cross-links: matched in real time against Drug Landscape's normalised drug + company + condition tables
Sponsor: as reported to ClinicalTrials.gov by Afferent Pharmaceuticals, Inc., a subsidiary of Merck & Co., Inc. (Rahway, New Jersey USA)
Last refreshed: 18 June 2019
Drug Landscape aggregates and links these public records for informational use only. Always verify against the primary source before clinical or regulatory decisions. Canonical URL: https://druglandscape.com/trial/NCT02476890.