In a non-human primate chronic cough model, Addex’s orally available GABAB positive allosteric modulator cut citric acid–induced cough frequency with efficacy comparable to baclofen. In prior guinea pig studies, the candidate reduced cough frequency, increased cough latency, showed no tolerance after sub-chronic dosing, and appeared more efficacious than nalbuphine, baclofen, codeine, and a P2X3 inhibitor. Tolerability and therapeutic margin were reported as better than nalbuphine, baclofen, and codeine, and broadly similar to a P2X3 inhibitor based on effects on respiratory rate.
The announcement marks a step-up from small-animal signal to a primate model for Addex’s independent chronic cough program, separate from its partnered GABAB PAM in substance use disorders. While still preclinical, the data give the company a mechanistically validated starting point for an IND path: leverage baclofen-like antitussive activity via allosteric potentiation without the dose-limiting CNS adverse effects and short half-life that constrain orthosteric GABAB agonists. The program targets once-daily, oral chronic use—an operationally straightforward profile in a field where class-specific tolerability has shaped development as much as efficacy.
Strategically, Addex is moving into a respiratory symptom market that remains unsettled. P2X3 antagonists have demonstrated activity but carry taste-related adverse events and a mixed U.S. regulatory history, leaving room for alternatives that can deliver meaningful cough-count reductions with cleaner tolerability. A GABAB PAM offers a familiar clinical hypothesis—replicate baclofen’s effect through modulation rather than direct agonism—while staying close to the company’s allosteric expertise. The bet is that PAM pharmacology widens the therapeutic window and avoids tolerance, converting an off-label, side-effect–burdened mechanism into a commercially viable label.
For sponsors, CROs, and sites, a GABAB-pathway entrant would likely follow the contemporary chronic cough playbook: objective 24-hour cough counts via validated ambulatory monitors as a primary endpoint, with treatment durations sufficient to assess durability and habituation. Operationally, that pushes toward centralized acoustic analytics, robust device logistics, and strict data integrity controls to manage placebo and diurnal variability. Safety monitoring will need to be built around CNS effects—sedation, dizziness, falls risk, driving considerations—rather than the dysgeusia profile seen with P2X3 agents, shifting AE adjudication and patient counseling. Comparator strategy will matter; regulators may accept placebo-controlled designs, but off-label baclofen use in some geographies could influence background therapy rules and rescue criteria. Recruitment will span pulmonology and ENT clinics, with potential to use cough-challenge substudies for pharmacodynamic anchoring.
Next, watch for IND-enabling milestones, first-in-human SAD/MAD timing, and whether Addex employs translational cough-challenge readouts to link exposure to effect ahead of patient trials. Dose selection and titration design will be critical to demonstrate a tolerability edge over baclofen without blunting efficacy. Financially, a small-cap sponsor will likely need a partner or targeted capital to run device-heavy, multicenter Phase 2 programs with extended follow-up. Key risks include translational uncertainty from primate and guinea pig models to human cough physiology, the potential emergence of class-typical CNS adverse events despite the PAM approach, and competitive timing against late-stage P2X3 programs and any shifting U.S. regulatory posture post-Europe/Japan precedents. If early human data reproduce the primate signal with a cleaner safety profile, the field could see a credible non-P2X3 path forward, but the burden of proof will rest on objective cough-count deltas, durability over 12-plus weeks, and a demonstrably wider therapeutic window.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
