Sarepta's $2.9 Million Gene Therapy Has a Liver Problem. Can a New Drug Fix It?

The Comeback Plan: Add Another Drug to the Mix

Now Sarepta is trying something new. As of March 16, 2026, the company began screening and enrolling patients for Cohort 8 of its ENDEAVOR study, an open-label Phase 1b trial. The goal: test whether adding a second immunosuppressive drug called sirolimus (also known as rapamycin) can prevent the liver damage that has plagued Elevidys.

Currently, patients already receive corticosteroids (a standard anti-inflammatory) around their infusion. The new regimen layers sirolimus on top, starting 14 days before the Elevidys infusion and continuing for 12 weeks afterward. It's like adding a second bouncer at the door: corticosteroids handle one type of immune overreaction, while sirolimus targets a different pathway.

The study plans to enroll approximately 25 non-ambulatory U.S. patients. Researchers will track two main things: how often acute liver injury occurs under the new protocol, and whether the therapy still produces meaningful levels of micro-dystrophin (the shortened protein Elevidys is designed to deliver) at 12 weeks.

If this works, it could reopen the door for non-ambulatory patients, the very population Sarepta was forced to walk away from last year.

Why This Matters Beyond Sarepta

Liver toxicity isn't unique to Elevidys. It's a known hazard across the entire class of AAV-based gene therapies (treatments that use adeno-associated viruses as delivery vehicles). Novartis' Zolgensma, a gene therapy for spinal muscular atrophy, has faced its own liver safety scrutiny.

So Sarepta isn't just solving its own problem. If the sirolimus protocol works, it could become a blueprint for the entire gene therapy field. Every company developing an AAV-based treatment is watching this trial closely.

The Commercial Tightrope

Many patients have received Elevidys across clinical trials and real-world use. In January 2026, Sarepta reported positive three-year Phase 3 data showing a 70% reduction in the rate of functional decline compared to what would be expected without treatment. No new safety signals emerged from that longer-term dataset.

That's genuinely impressive efficacy. The problem is that efficacy only matters if doctors feel comfortable prescribing the drug, and parents feel comfortable saying yes.

The $2.9 million price tag already makes Elevidys a tough sell to insurers. Add a Boxed Warning for fatal liver failure, and the commercial headwinds get fierce. Losing the non-ambulatory population further narrows the addressable market. Every DMD family weighing Elevidys now has to do a gut-wrenching cost-benefit calculation with "death" sitting on one side of the ledger.

The Competition Isn't Sitting Still

Sarepta still has first-mover advantage, but the field is catching up. Regenxbio's RGX-202 is advancing in Phase 3 with dosing planned for 2026. Solid Biosciences' SGT-003 has key clinical updates expected this year. Meanwhile, companies like Dyne Therapeutics and Avidity Biosciences are taking a completely different approach, using antibody-targeted delivery systems for DMD.

Wave Life Sciences is pushing its exon-skipping therapy WVE-N531 toward an NDA submission in 2026. And Avidity's del-zota already launched a managed access program in November 2025, giving select patients early access before a potential approval.

If Sarepta can't resolve the liver safety issue, these competitors won't just nibble at market share. They'll devour it.

The Bottom Line

Sarepta built something remarkable with Elevidys: a one-time gene therapy for a disease that previously had no curative options. But "one-time" only works if the single dose doesn't cause irreversible harm.

The ENDEAVOR Cohort 8 trial is arguably the most important study in Sarepta's pipeline right now. Not because it tests a new therapy, but because it tests whether the existing one can be made safe enough to fulfill its original promise. Twenty-five patients will help determine if sirolimus is the missing piece of the puzzle, or if Elevidys' liver problem is more fundamental than an immune response gone haywire.

For the DMD community, the stakes couldn't be higher. These families have waited decades for a gene therapy. They finally got one. Now they need it to be safe enough to actually use.

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