Amondys 45 (casimersen)
An approved treatment for Duchenne Muscular Dystrophy.
The same compound appears under different names depending on the context. Here is how to identify Casimersen wherever you encounter it, plus the key facts at a glance.
- Generic name
- Casimersen
- Brand name
- Amondys 45
- Development code
- SRP-4045
- Drug class
- Antisense oligonucleotide (exon skipping)
- Manufacturer
- Sarepta Therapeutics
- How it's taken
- Given as a weekly intravenous infusion over 35-60 minutes at a dose of 30 mg/kg.
An exon 45 skipping therapy for DMD patients whose dystrophin gene mutation is amenable to skipping exon 45, representing about 8% of the DMD population.
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Where Casimersen fits
Exon 45 skipping therapy for DMD, expanding the range of mutations treatable with exon-skipping technology. Applicable to roughly 8% of DMD patients.
How Casimersen works
Casimersen tells cells to skip over exon 45 in the dystrophin gene, allowing production of a shorter but partially functional dystrophin protein. This targets a different subset of DMD patients than the exon 51 or exon 53 skipping drugs.
Mechanism: Antisense oligonucleotide that enables exon 45 skipping to produce shortened but functional dystrophin
Side effects and safety
Common side effects include upper respiratory tract infection, cough, fever, headache, joint pain, and throat pain. Serious allergic reactions, including swelling of the face or throat and anaphylaxis, have occurred. Kidney damage was seen in animal studies and with some similar medicines, so kidney tests are done before starting and regularly during treatment.
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Casimersen
Given as a weekly intravenous infusion over 35-60 minutes at a dose of 30 mg/kg.
Availability and cost
Only available as the brand-name product.
Antisense oligonucleotide for exon 45 skipping, applicable to a subset of DMD patients. Ultra-orphan mutation-specific therapy.
Help paying for Amondys 45
Pick your insurance to see which help fits. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE; charity funds are the usual route there.
- Insurance and case manager help
A dedicated SareptAssist Case Manager helps with insurance approvals and coordinating AMONDYS 45 delivery.
The official page does not say who qualifies. Ask the program. · source - Copay help
Co-pay Assistance Program may help commercially insured patients with co-pays, co-insurance and deductibles. Not for government insurance like Medicare.
For: private insurance · source - Free medicine program
Case Managers can share information on a Sarepta Patient Assistance Program. Eligibility is not described on the official pages.
The official page does not say who qualifies. Ask the program. · source
Good to know: Call 1-888-SAREPTA (Mon-Fri 8:30am-6:30pm ET). Copay terms are on Sarepta's corporate SareptAssist page, which covers 'a Sarepta product'. Who qualifies for the Patient Assistance Program is not stated on official pages; ask the Case Manager.
- From a charity · NORD RareCareDuchenne Muscular Dystrophy Medical Assistance fundOpen
Pays for: Medical and medication costs.
The foundation says: “Accepting new applications and re-enrollments for current year” - From a charity · NORD RareCareDuchenne Muscular Dystrophy Premium Copay Assistance fundOpen
Pays for: Insurance premiums and copays.
The foundation says: “Accepting new applications and re-enrollments for current year” - From a charity · The Assistance FundDuchenne Muscular Dystrophy fundOpen
Pays for: Copays, coinsurance, deductibles and other health-related expenses.
The foundation says: “OPEN — Accepting New Patients. TAF is currently accepting new patient enrollments for this program.” - From a charity · Muscular Dystrophy AssociationMDA Durable Medical Equipment (DME) Grant Program fundApply directly
Pays for: Medical equipment (wheelchairs, lifts, canes and other DME), up to $1,000 per year.
The foundation says: “Status not shown on page”
Access and eligibility
Amondys 45 is only for patients with a confirmed DMD gene mutation amenable to exon 45 skipping, which applies to a subset of DMD patients.
Source: Amondys45.com (Sarepta Therapeutics)
Access program details are provided for informational purposes and may vary based on insurance coverage, geographic location, and individual circumstances. Confirm current eligibility directly with the manufacturer or your specialty pharmacy.
Clinical trial results
Approved February 2021 under accelerated approval. An interim analysis of the ESSENCE study showed statistically significant increases in dystrophin production versus baseline and placebo. The completed ESSENCE trial (225 boys aged 6 to 13, reported November 2025) did not reach statistical significance on its main goal, 4-stair climb speed at 96 weeks. The FDA is reviewing a request for traditional approval, with a decision due by February 28, 2027.
Development history
Casimersen was the fourth exon-skipping therapy approved for DMD and the third from Sarepta. Together with eteplirsen and golodirsen, Sarepta's portfolio covers approximately 29% of the DMD population.
Explore Duchenne Muscular Dystrophy trials
Other Duchenne Muscular Dystrophy treatments
Common questions about Casimersen
▸What is Casimersen (Amondys 45)?
An exon 45 skipping therapy for DMD patients whose dystrophin gene mutation is amenable to skipping exon 45, representing about 8% of the DMD population.
▸How does Casimersen work?
Casimersen tells cells to skip over exon 45 in the dystrophin gene, allowing production of a shorter but partially functional dystrophin protein. This targets a different subset of DMD patients than the exon 51 or exon 53 skipping drugs.
▸What are the side effects of Casimersen?
Common side effects include upper respiratory tract infection, cough, fever, headache, joint pain, and throat pain. Serious allergic reactions, including swelling of the face or throat and anaphylaxis, have occurred. Kidney damage was seen in animal studies and with some similar medicines, so kidney tests are done before starting and regularly during treatment.
▸How is Casimersen taken?
Given as a weekly intravenous infusion over 35-60 minutes at a dose of 30 mg/kg.
▸Is Casimersen FDA approved?
Yes, Casimersen (Amondys 45) is FDA approved (2021) for the treatment of Duchenne Muscular Dystrophy.
▸What percentage of DMD patients can benefit from casimersen?
Approximately 8% of DMD patients have mutations amenable to exon 45 skipping. Together with eteplirsen (exon 51, ~13%) and golodirsen/viltolarsen (exon 53, ~8%), the three exon targets cover roughly 29% of the DMD population. Genetic testing is required to determine which exon-skipping therapy, if any, is appropriate for a given patient.
▸How does the ESSENCE study support casimersen?
ESSENCE tested casimersen and golodirsen against placebo. An early look at muscle biopsies showed a statistically significant increase in dystrophin with casimersen compared with baseline and placebo, and this formed the basis for the FDA's accelerated approval in February 2021. Topline results from the completed study, reported in November 2025, did not show a statistically significant benefit on the main goal, the speed of climbing 4 stairs after 96 weeks, although the numbers trended in favor of treatment. Sarepta has asked the FDA to convert Amondys 45 to traditional approval using ESSENCE and real-world data, and the FDA's decision is due by February 28, 2027.
▸Can casimersen be used with gene therapy?
The interaction between exon-skipping therapy and gene therapy (Elevidys) has not been formally studied. In theory, exon-skipping targets the patient's native dystrophin gene while gene therapy provides an entirely new micro-dystrophin gene, so they could potentially be complementary. However, the decision to combine or sequence these treatments should be made by a neuromuscular specialist familiar with both approaches.
▸Is casimersen given for life?
Yes. Like all exon-skipping therapies, casimersen requires ongoing weekly IV infusions. The drug works at the RNA level and does not permanently alter DNA, so its effect is temporary and continuous treatment is needed to maintain dystrophin production.