Pemvidutide MASH trial: liver fibrosis improvement with near-zero dropouts in IMPACT Phase 2b

TL;DR

Altimmune's pemvidutide - a once-weekly injectable that simultaneously agonises GLP-1 and glucagon receptors - produced significant liver fibrosis improvement and MASH (metabolic dysfunction-associated steatohepatitis) resolution in the IMPACT Phase 2b trial. The drug showed an exceptionally low discontinuation rate, separating it from other liver disease candidates that have struggled with tolerability. Phase 3 planning is underway following these results published in December 2025.

Metabolic dysfunction-associated steatohepatitis (MASH) - formerly called NASH - is a form of fatty liver disease that has progressed from simple fat accumulation to active liver inflammation and fibrosis (scarring). Left untreated, MASH progresses to cirrhosis, liver failure, and hepatocellular carcinoma. An estimated 38 million people in the US have MASH, and until recently there was no approved pharmacotherapy. The GLP-1 class has entered this space, with semaglutide showing strong MASH efficacy and pemvidutide pushing the boundary further with its dual mechanism.

What pemvidutide is and why glucagon matters for liver disease

Pemvidutide is structurally distinct from semaglutide and tirzepatide. Instead of combining GLP-1 with GIP (as tirzepatide does), pemvidutide combines GLP-1 with glucagon receptor agonism. Glucagon is typically known as the counter-regulatory hormone to insulin - it raises blood sugar when glucose falls. But glucagon also has direct effects on liver fat metabolism that are distinct from its glycaemic function.

In the liver, glucagon receptor activation:

• Promotes fatty acid oxidation - burning stored fat rather than accumulating it
• Reduces lipogenesis - decreasing new fat synthesis in the liver
• Increases very-low-density lipoprotein (VLDL) secretion - exporting liver fat to other tissues
• Directly stimulates hepatic glucose production (which is why glucagon raises blood sugar)

The GLP-1 component of pemvidutide counteracts the hyperglycaemic effect of glucagon, meaning the GLP-1/glucagon combination can achieve the liver fat-clearing benefits of glucagon without raising blood sugar. This is the theoretical advantage over GLP-1 alone for MASH: pemvidutide hits the liver's fat metabolism more directly than semaglutide, potentially producing faster and deeper liver fat reduction.

The IMPACT Phase 2b results

The IMPACT trial enrolled adults with biopsy-confirmed MASH and liver fibrosis (stage F1-F3). Primary endpoints were liver fibrosis improvement of at least one stage without worsening of MASH, and MASH resolution without worsening of fibrosis - the two standard FDA-recognised histological endpoints for MASH drug approval.

Results at the trial's primary endpoint timepoint:

• Liver fibrosis improvement (one or more stages, no MASH worsening): statistically significant improvement vs placebo
• MASH resolution (no active steatohepatitis, no MASH worsening): statistically significant improvement vs placebo
• Liver fat reduction measured by MRI-PDFF: substantial reductions from baseline, consistent with the drug's dual mechanism targeting hepatic lipid metabolism
• Weight loss: significant body weight reduction as expected from GLP-1 agonism

The dropout rate was exceptionally low - a standout figure in a disease area where clinical trials frequently struggle with tolerability-related discontinuations. MASH trial populations often include patients with advanced metabolic disease who are particularly vulnerable to GI side effects. Pemvidutide's near-zero dropout rate suggests a tolerability profile that may support real-world adherence better than some competitors.

How pemvidutide compares in the MASH landscape

The MASH treatment landscape has become crowded rapidly. Resmetirom (Rezdiffra), a thyroid hormone receptor beta agonist, received the first-ever FDA approval for MASH in March 2024 - the landmark that opened this field to serious investment. Semaglutide showed a 62.9% MASH resolution rate vs 34.3% placebo in a 72-week Phase 3 trial, establishing GLP-1 as a serious MASH therapeutic. Lanifibranor, survodutide, and other candidates are in Phase 3.

Pemvidutide's GLP-1/glucagon mechanism offers a potentially differentiated profile - particularly in terms of liver fat reduction speed and magnitude. The glucagon component's direct promotion of hepatic fat oxidation may produce faster liver fat clearance than GLP-1 alone, which is important in MASH because liver fat is the fuel driving the inflammatory cascade that causes fibrosis. Removing it faster may translate to better histological outcomes.

The tolerability advantage

In MASH drug development, the graveyard of failed trials is littered with compounds that worked in principle but caused too many side effects in practice. Obeticholic acid (Ocaliva) was approved for primary biliary cholangitis and showed MASH efficacy but caused severe pruritus (itching) in many patients. Several FXR agonists and PPAR agonists have failed to reach approval partly due to tolerability. Pemvidutide's low dropout rate in IMPACT is therefore not just a clinical footnote - it signals a drug that patients can actually stay on long enough to benefit from.

What MASH patients need to know about GLP-1 nutrition

MASH patients already face significant nutritional complexity. Impaired liver function affects vitamin D activation (the liver converts vitamin D from its storage form to the active form), cholesterol metabolism, B12 storage, and fat-soluble vitamin absorption. Adding a GLP-1-based therapy that further suppresses appetite and reduces food intake compounds the nutritional challenge. MASH patients on GLP-1-based therapies - whether semaglutide, tirzepatide, or in future pemvidutide - have a particularly strong rationale for targeted nutritional support.

Key nutrients at risk include vitamin D (critical for liver function and already impaired in MASH), B12, magnesium, and zinc. GLP-1 Shield addresses the documented nutrient gaps of GLP-1 therapy with a formulation designed for the specific deficiency patterns GLP-1 medications create.

Frequently asked questions

What is pemvidutide and how does it differ from Ozempic?

Pemvidutide is a once-weekly injectable GLP-1/glucagon dual agonist developed by Altimmune. Unlike semaglutide (Ozempic, Wegovy), which only activates GLP-1 receptors, pemvidutide simultaneously activates glucagon receptors. In the liver, glucagon activation directly promotes fat oxidation and reduces fat synthesis - making pemvidutide particularly targeted for liver fat reduction in MASH. The GLP-1 component offsets glucagon's blood-sugar-raising effect.

What is MASH and is it the same as NASH?

MASH (metabolic dysfunction-associated steatohepatitis) is the new name for what was previously called NASH (nonalcoholic steatohepatitis). The terminology changed in 2023 to better reflect the metabolic drivers of the disease and remove the misleading "nonalcoholic" framing. MASH is fatty liver disease that has progressed to active liver inflammation and early scarring (fibrosis), distinguishing it from simple fatty liver (steatosis) without inflammation.

Is pemvidutide approved for MASH?

No. As of June 2026, pemvidutide is not approved for MASH. IMPACT Phase 2b results published in December 2025 were positive, and Altimmune is planning Phase 3. Based on standard timelines, potential FDA approval would be 2028-2029 at the earliest. The only FDA-approved pharmacotherapy for MASH as of 2026 is resmetirom (Rezdiffra), approved in March 2024. Semaglutide is likely to receive MASH approval in 2025-2026 based on its Phase 3 results.

Can Ozempic or Wegovy treat MASH?

Semaglutide showed a 62.9% MASH resolution rate vs 34.3% for placebo in a Phase 3 MASH trial. An FDA approval for semaglutide in MASH is likely in 2025-2026. Tirzepatide also showed strong MASH efficacy in the SYNERGY-NASH trial. GLP-1 medications as a class are now considered among the most effective available pharmacological treatments for MASH, with approval for this specific indication pending or expected soon.