Casimersen (Amondys 45TM) is well tolerated and significantly increased dystrophin expression at 48 weeks after treatment initiation, according to interim results from the phase 3 ESSENCE clinical trial.

Researchers presented the results, from a prespecified interim analysis of 48-week muscle biopsy data, at the 2022 Muscular Dystrophy Association Clinical & Scientific Conference.

ESSENCE is a long-term multicenter study evaluating the safety and efficacy of casimersen as well as golodirsen (Vyondys 53™)  in patients with Duchenne muscular dystrophy (DMD).

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The first part of the trial lasts 96 weeks and is double-blind and randomized. This is followed by an open-label extension study lasting 48 weeks. The primary outcome measure is the change from baseline in the total 6-minute walk distance at Week 96. Secondary outcome measures include the change from baseline in levels of dystrophin, patients’ ability to independently rise from the floor, and time to loss of ambulation.

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Patients with DMD amenable to exon 45 skipping, aged 7 to 13 years, randomly received either 30 mg/kg of casimersen or a placebo intravenously once a week.

The interim results showed that patients treated with casimersen had significant increases in exon 45 skipping. They also had significantly higher mean dystrophin levels from baseline after 48 weeks and compared with placebo. The increased expression of dystrophin positively correlated with exon skipping.

The researchers concluded that this demonstrated a mechanistic association between exon 45 skipping and de novo dystrophin production. Importantly, the produced dystrophin was correctly localized to the sarcolemma. 

Patients tolerated the treatment well with no signs of renal toxicity, according to a poster presented at the conference. Most adverse events were mild and not related to the treatment.

The trial is still recruiting participants at 67 study locations across the world. It is expected to be completed on April 30, 2024.

Casimersen is an exon-skipping therapy by Sarepta Therapeutics approved by the US Food and Drug Administration to treat DMD patients who are amenable to exon 45 skipping. 


Iannaccone S, Phan H, Straub V, et al. Casimersen in patients with Duchenne muscular dystrophy amenable to exon 45 skipping: Interim results from the phase 3 ESSENCE trial. Poster presented at: 2022 Muscular Dystrophy Association Clinical & Scientific Conference; March 13-16, 2022; Nashville, TN. Poster 49.

Study of SRP-4045 and SRP-4053 in participants with Duchenne muscular dystrophy (DMD) (ESSENCE). US National Library of Medicine. Last updated August 19, 2021. Accessed March 10, 2022.