Respiratory · Clinical trials
Chronic Cough Clinical Trials
Approved therapies, the pivotal-trial endpoints they were judged on, the magnitude of benefit — and the drugs that failed their endpoints, and why.
Indication overview
About chronic cough — and why its trials are hard
Chronic cough is a cough lasting more than eight weeks. Many cases stem from identifiable causes such as asthma, gastroesophageal reflux, upper-airway cough syndrome, ACE inhibitors or smoking, and improve when the underlying condition is treated. However, a substantial subset persists despite thorough evaluation and guideline-based therapy, termed refractory chronic cough, or remains without identifiable cause, unexplained chronic cough. This population is thought to have cough hypersensitivity driven by sensitized airway sensory neurons, with the P2X3 receptor on vagal afferents implicated as a key mediator. Refractory chronic cough substantially impairs quality of life through exhaustion, urinary incontinence, social embarrassment and sleep disruption, yet in the United States there is no FDA-approved therapy. Off-label neuromodulators such as gabapentin, pregabalin, amitriptyline and morphine, plus speech-pathology cough-suppression therapy, are used with limited evidence. The lead candidate, the P2X3 antagonist gefapixant, was rejected by the FDA despite approvals abroad. Objective 24-hour cough frequency is the pivotal efficacy endpoint in registrational trials.
Where trials have failed
Drugs that missed their endpoint — and what contributed
The most instructive lessons in chronic cough development come from programmes that failed the endpoint that mattered.
| Drug / trial | Endpoint outcome | What contributed |
|---|---|---|
| gefapixant (P2X3 antagonist) — COUGH-1 and COUGH-2 (Phase 3) | FDA issued a Complete Response Letter in 2022 declining approval; an advisory committee voted 12-1 against efficacy in November 2023 and a second CRL followed, so it remains unapproved in the US despite EU/Japan approval (Lyfnua) | Modest absolute reduction in 24-hour cough frequency, a very large placebo response, concerns about the measurement/analysis methodology, and frequent taste-related adverse events (dysgeusia) causing dropouts |
| orvepitant (NK1 antagonist) — VOLCANO-2 and subsequent Phase 2 program | Did not achieve convincing, consistent reductions in cough frequency to support advancement | Insufficient effect size over placebo in the refractory-cough population led to program deprioritization (unverified specifics) |
Choosing the right endpoint
Primary endpoints that matter in chronic cough trials
- 24-hour cough frequency (objective) — Pivotal endpoint measured by ambulatory acoustic cough monitoring
- Awake cough frequency — Alternative objective monitoring window used in some trials
- Leicester Cough Questionnaire (LCQ) — Validated cough-specific quality-of-life patient-reported measure
- Cough Severity VAS / Cough Severity Diary — Patient-reported severity endpoints supporting objective counts
- Placebo response magnitude — A critical analytic consideration given the large placebo effect seen in cough trials
How iNGENū runs chronic cough trials
Physician-led design, built for FDA submission
Endpoint & biomarker strategy
Board-certified specialists design endpoints and patient selection aligned to current FDA guidance for this indication.
FDA-ready data
Built to ICH-GCP and 21 CFR 312.120, with direct FDA submission — data accepted by the FDA, EMA and MHRA.
Faster, lower-cost delivery
~4-week ethics via the TGA CTN scheme, up to 43.5% R&D rebate, and 80–90% below US CRO cost.
Request a fixed-milestone proposal and a tailored endpoint & feasibility summary for this indication.
Frequently asked questions
Chronic Cough clinical trials — FAQs
Is there an FDA-approved drug for refractory chronic cough?
What happened with gefapixant?
Why is chronic cough so hard to treat?
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