CALM Phase 3 Trial Failure and Development Halt

GSK plc (GSK), a global pharmaceutical company based in the UK, has officially discontinued the development of camlipixant, a drug candidate for refractory chronic cough (RCC) acquired through the acquisition of Bellus Health. The decision follows inconsistent results from the pivotal Phase 3 trials, CALM-1 and CALM-2, which failed to demonstrate efficacy. In CALM-1, which evaluated data at week 12, the 50mg twice-daily dose group showed a statistically significant reduction in the frequency of cough over 24 hours compared to placebo, meeting the primary endpoint. However, CALM-2, which evaluated data at week 24, did not achieve statistical significance. The lower dose of 25mg failed in both trials and did not meet the key secondary endpoints, leading GSK management to conclude that the efficacy of camlipixant is limited.

$2 Billion Asset Write-Down and M&A Risk Highlighted

This development halt signifies the complete loss of the blockbuster potential that GSK had anticipated when it acquired Bellus Health in April 2023 for a total of $2.0 billion in an all-cash transaction. At the time, GSK invested heavily to strengthen its leadership in respiratory diseases, but this failure has significantly impacted the efficiency of its research and development (R&D) investments, making a large asset write-down inevitable. This serves as a reminder that even late-stage assets in biotech M&A still carry significant scientific failure risk. However, GSK is expected to reallocate resources to its oncology portfolio, where it has been focusing its efforts, to restructure its mid- to long-term growth strategy.

P2X3 Receptor-Targeting Drugs Face Consecutive Setbacks

Camlipixant is a P2X3 receptor antagonist, a class of drugs that modulate the cough reflex. This failure is another example of the consecutive setbacks faced by drugs with the same mechanism of action. Previously, gefapixant from MSD (Merck & Co., MRK) received two Complete Response Letters (CRLs) from the US FDA due to lack of efficacy, and Bayer's eliapixant was voluntarily discontinued in Phase 2. This failure further demonstrates that the P2X3 receptor has significant development challenges and that this mechanism has clear limitations in treating chronic cough. The industry's skepticism about this mechanism is likely to deepen.

Market Opportunity for Competing Companies

GSK's setback has reshaped the global chronic cough treatment market, creating a monopoly opportunity for certain competitors. The global chronic cough market is estimated at approximately $10.4 billion in 2025 and is expected to continue to grow. With both gefapixant and camlipixant eliminated, Trevi Therapeutics (TRVI), which is developing haduvio, a drug with a novel mechanism of action as a kappa opioid receptor agonist/mu opioid receptor antagonist, has emerged as the biggest beneficiary. Trevi is conducting a Phase 3 trial for haduvio, and concerns about its market potential have eased following the failures of its competitors, leading to a 16% surge in its stock price in a single day.