GSK Abandons Camlipixant as Superior Tolerability Fails to Compensate for Inconsistent Efficacy

GSK Halts Camlipixant Chronic Cough Program After Phase 3 Failures

GSK has decided to discontinue the development of camlipixant for refractory chronic cough following mixed results from its Phase 3 CALM-1 and CALM-2 trials. While CALM-1 met its primary endpoint, showing a significant reduction in 24-hour cough frequency at 12 weeks with a 50-mg dose, CALM-2 failed to demonstrate a significant decrease. Both trials also missed key secondary endpoints, leading GSK to conclude that camlipixant is unlikely to transform patient care for refractory chronic cough. The drug was acquired through a $2 billion buyout of Bellus Health in April 2023.

• GSK's camlipixant demonstrated mixed efficacy in its pivotal Phase 3 program for refractory chronic cough. The CALM-1 trial successfully met its primary endpoint, showing a significant reduction in 24-hour cough frequency at 12 weeks with a 50-mg dose compared to placebo. However, the CALM-2 trial did not achieve a significant decrease in cough frequency, and both trials failed to meet their key secondary endpoints, indicating an inconsistent efficacy profile.
• Following the disappointing late-stage performance, GSK has announced it will no longer invest in the development of camlipixant for refractory chronic cough. The company stated that the drug's efficacy profile suggests it is "unlikely to transform patient care" for this condition, leading to the strategic decision to abandon the refractory chronic cough program despite a prior $2 billion acquisition of Bellus Health for this asset.
• The discontinuation of camlipixant for refractory chronic cough marks a significant shift for GSK, which had acquired Bellus Health in April 2023 for $2 billion specifically for this P2X3 antagonist. This decision follows a competitive landscape where Merck's gefapixant, another P2X3 antagonist, also faced FDA rejections for refractory chronic cough. GSK will, however, continue to explore camlipixant's potential in irritable bowel syndrome, where it is currently in mid-stage development.

GSK's Camlipixant: Unpacking the Phase 3 CALM Trial Results

A recent feasibility pilot, the CoughRetrain Program study, evaluated a theory-informed telehealth behavioral intervention for adults with refractory chronic cough (RCC). The program, delivered over five individual sessions, integrated education, graded suppression practice, motivational interviewing, and goal setting. Among the 11 participants who completed the study, the intervention demonstrated promising efficacy, with a mean increase of 3.6 points on the Leicester Cough Questionnaire (LCQ) and a mean decrease of 18.8 mm on the cough severity visual analogue scale (CS-VAS). Additionally, a 48% reduction in 24-hour objective cough frequency was observed. The intervention was found to be safe and feasible, with only two non-serious adverse events reported and no treatment discontinuations.

On the pharmacological front, recent studies have explored neuromodulators and opioid agonists for chronic cough. The Phase 2b CORAL study investigated nalbuphine for idiopathic pulmonary fibrosis (IPF)-associated cough. Despite its mechanism as a µ-receptor antagonist/partial agonist and κ-receptor agonist, which was hypothesized to offer a better safety profile than morphine, treatment with nalbuphine resulted in common adverse events, and cough rates remained relatively high. In a separate study of pregabalin for chronic neurogenic cough, the agent was described as a well-tolerated neuromodulator. However, while only 4% of patients discontinued due to side effects, 17% did not report improvement. These results highlight the ongoing need for therapies with an improved balance of efficacy and safety.

The Persistent Challenge of Refractory Chronic Cough Treatment

Refractory chronic cough (RCC) is a persistent cough lasting over eight weeks that does not resolve despite optimal management of underlying conditions such as asthma or GERD. This debilitating condition poses a significant clinical challenge due to the historical lack of targeted, approved therapies and the substantial limitations of existing off-label treatment strategies.

• Absence of Approved, Accessible Therapies: A primary limitation is the lack of broadly accessible, licensed pharmacological agents for RCC. Until very recently, no specific therapies had been approved, forcing clinicians to rely on off-label medications that do not target the underlying pathophysiology of cough hypersensitivity.

• Limited Efficacy of Current Off-Label Treatments: Neuromodulators like gabapentin, a common off-label approach, demonstrate imperfect efficacy and high rates of treatment failure. In a real-world study, while over half of patients responded to a given neuromodulator, one-third still required alternative treatments due to poor initial response, and relapse remains common upon dose reduction or withdrawal.

• Poor Tolerability and Significant Side Effects: The use of current off-label treatments is often constrained by a poor safety and tolerability profile. Side effects such as sedation are frequently reported with neuromodulators, which can limit their use and lead to patient non-adherence.

• Ineffectiveness of Standard Antitussives: By definition, RCC does not respond well to standard interventions. This includes over-the-counter cough medications and therapies directed at associated conditions, which are often prescribed before an RCC diagnosis is made.

• Poor Response in Specific Patient Subgroups: Certain patient populations demonstrate a particularly poor response to available treatments, highlighting the challenge of patient heterogeneity. For example, carriers of biallelic RFC1 repeat expansions are often diagnosed with RCC, have a longer cough duration, and show a poor response to antitussive therapies.

• Nascent Stage of Non-Pharmacological Options: The clinical application of non-pharmacological therapies is still in its early stages. While approaches like speech and language therapy are being explored, they are not yet widely established, necessitating further research to validate their role in RCC management.

P2X3 Antagonists: A Shifting Landscape in Chronic Cough

Camlipixant, a selective P2X3 receptor antagonist, is being developed for refractory chronic cough (RCC) and is currently in Phase III trials. Several other agents share this mechanism of action, though most are dual P2X2/3 antagonists or selective P2X3 antagonists with varying trial designs. Together, these molecules have been evaluated in comprehensive meta-analyses encompassing thousands of patients across multiple randomized controlled trials.

Aggregate Evidence Base:

• A systematic review and network meta-analysis pooled data from 16 RCTs (N=4,904) across all five P2X3 receptor antagonists (gefapixant, sivopixant, eliapixant, camlipixant, filapixant).

• A separate systematic review identified 9 RCTs (21 active arms; N=1,934) evaluating purinergic receptor antagonists specifically in refractory chronic cough.

• A key distinguishing trial design feature across the class: selective P2X3 antagonists (camlipixant, sivopixant, eliapixant, filapixant) were developed to mitigate the taste disturbance (dysgeusia) associated with dual P2X2/3 blockade seen with gefapixant, reflecting a deliberate pharmacological differentiation strategy embedded in trial endpoints and safety monitoring across these programs.

Refractory Chronic Cough: A High Bar for P2X3 Antagonist Development

The discontinuation of camlipixant by GSK represents a pivotal moment for the refractory chronic cough landscape and the P2X3 receptor antagonist class. For patients suffering from this debilitating condition, who currently have limited effective treatment options, this news is undoubtedly disappointing. The P2X3 mechanism has long been heralded as a promising avenue, targeting the neuronal hypersensitivity that drives chronic cough. Indeed, earlier studies with P2X3 antagonists like gefapixant demonstrated significant reductions in cough frequency and improvements in cough-specific quality of life, although often accompanied by taste disturbances.

Camlipixant itself showed promise in Phase 2b, with a notable reduction in cough frequency and a seemingly more favorable taste alteration profile compared to some other P2X3 antagonists. However, the mixed results from its Phase 3 program—where one trial met its primary endpoint but the other did not, and both missed key secondary endpoints—underscore the profound challenge of consistently demonstrating a clinically meaningful benefit in this patient population. This outcome suggests that even a statistically significant reduction in cough frequency may not be sufficient if it doesn't translate into a robust and consistent improvement in patients' daily lives, especially when considering potential side effects.

For GSK, this decision carries significant financial implications, following a substantial acquisition. Strategically, it reinforces the need for rigorous and consistent data across multiple endpoints in late-stage development, particularly for novel mechanisms. For the broader P2X3 antagonist class, while the mechanism remains validated by other agents like gefapixant, camlipixant's failure raises the bar for future candidates. Developers must now not only demonstrate efficacy but also a highly consistent and superior benefit-risk profile, potentially through more refined patient selection or novel formulations that mitigate taste-related adverse events, to truly transform care for refractory chronic cough.