- GSK investigational efimosfermin (BOS-580), a long-acting FGF21 subcutaneous injection, is being developed for MASH.
- Phase II 48-week data showed fibrosis improvement and MASH resolution in patients with F2/F3 fibrosis versus placebo.
- Phase III ZENITH-1 and ZENITH-2 are ongoing in F2/F3 patients, and Phase III trials in F4 (cirrhotic) MASH are expected to start in 2026.
- Safety in trials was generally well tolerated with mild, transient gastrointestinal adverse events (nausea, vomiting, diarrhoea).
Regulatory designations
Efimosfermin has received FDA Breakthrough Therapy designation and EMA PRIME designation for the treatment of metabolic dysfunction-associated steatohepatitis (MASH).
Clinical data
Phase II data at 48 weeks in patients with F2/F3 fibrosis showed fibrosis improvement and MASH resolution versus placebo; safety was generally well tolerated with mild, transient gastrointestinal adverse events (nausea, vomiting, diarrhoea).
Development status and timeline
Efimosfermin is in Phase III (ZENITH-1 and ZENITH-2) for F2/F3 MASH; Phase III trials in F4 (cirrhotic) MASH are expected to start this year.
Drug profile
Efimosfermin (BOS-580) is a once-monthly subcutaneous injection of a long-acting FGF21 variant designed to reduce liver fat, reduce inflammation and reverse fibrosis; it is investigational and not available for prescription.
Disease context
MASH is a chronic, progressive liver disease affecting up to 5% of the global population and is a leading cause of liver transplant in the US and Europe, with fibrosis the key predictor of serious outcomes.
