Generic name: casimersen [ KAS-i-MER-sen ]
Dosage form: intravenous infusion
Drug class: Miscellaneous uncategorized agents

Medically reviewed by Melisa Puckey, BPharm. Last updated on Apr 3, 2025.

What is Amondys 45?

Amondys 45 (casimersen) is a prescription medication used to treat Duchenne muscular dystrophy (DMD) with a specific genetic mutation in the DMD gene that is treatable with exon 45 skipping. Amondys 45  works by targeting the exon 45 part of the dystrophin gene to help the body make an effective dystrophin protein, which improves muscle stability and may slow disease progression. This mutation will be confirmed through genetic testing before starting treatment.

Amondys 45 is administered as a once weekly intravenous infusion, over 35 to 60 minutes.

Amondys 45 FDA approval was granted on February 25, 2021, dystrophy (DMD) with a specific genetic mutation in the DMD gene that is treatable with exon 45 skipping. Amondys 45 FDA approval was based on positive results from the ESSENSE trial (NCT02500381) showing Amondys 45 patients had a statistically significant increase in muscle dystrophin levels, which is reasonably likely to predict clinical benefit. 

Amondys 45 FDA approval is an accelerated approval, and continued approval may require further clinical studies to confirm its long-term benefits in slowing disease progression.

Amondys 45 manufacturer is Sarepta Therapeutics.

What is Duchenne Muscular Dystrophy (DMD) Amenable to Exon 45 Skipping?

Duchenne muscular dystrophy (DMD) is a genetic disorder that causes progressive muscle weakness and degeneration, primarily in boys. It results from mutations in the DMD gene, which disrupt the production of dystrophin, a protein essential for muscle stability.

How Does Exon 45 Skipping Work?

Some DMD mutations lead to missing exons, preventing functional dystrophin protein production. Exon 45 skipping is a targeted therapy that restores part of the gene’s reading frame, allowing the body to produce a shortened but functional dystrophin protein, potentially slowing muscle degeneration.

Amondys 45 (casimersen) is designed for patients with DMD mutations amenable to exon 45 skipping. A genetic test will confirm eligibility for treatment.

How Does Amondys 45 Work?

Amondys 45 mechanism of action is as an antisense oligonucleotide that targets exon 45 of the dystrophin gene, promoting the production of a partially functional dystrophin protein to help stabilize muscles and slow disease progression.

Amondys 45 side effects

Common side effects

Common Amondys 45 side effects include: 

• Upper respiratory tract infections (65%)
• Cough (33%)
• Fever (33%)
• Headache (32%)
• Joint pain (21%)
• Mouth and throat pain (21%)

These common side effects occurred in 20% or more of Amondys 45 patients in Study 1 (NCT02500381).

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Serious side effects

Get emergency medical help if you have signs of an allergic reaction: hives, itching, rash, blistering, or peeling; fever; difficulty breathing; swelling of your face, lips, tongue, or throat.

Amondys 45 may cause serious side effects. Call your doctor at once if you have:

• pink, brown, or red urine;
• foamy urine; or
• swelling in your face, hands, feet, or stomach.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Warnings 

Before using this medicine, tell your doctor if you have:

•  Kidney disease or a history of kidney problems
•  Any allergies to medications
• A history of infusion-related reactions.

Do not use this medicine if you are allergic to the active ingredient, casimersen, or any of the inactive ingredients.

Pregnancy or breastfeeding

Pregnant or breastfeeding women should discuss potential risks with their healthcare provider, as the effects of Amondys 45 on fetal development are unknown.

What happens if I miss a dose?

Call your doctor for instructions if you miss an appointment for your Amondys 45.

What happens if I overdose?

Since Amondys 45 is given by a healthcare professional in a medical setting, an overdose is unlikely to occur.

What should I avoid while taking this medicine?

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

What other drugs will affect this medicine?

Other drugs may affect Amondys 45, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop. This is not a complete list of interactions.

Amondys 45 Package Insert 

HCPs and patients often use the Amondys 45 Package Insert for more detailed information about this medicine. The Package Insert contains more comprehensive information on Indications and Usage, Dosage and Administration, Clinical Pharmacology, Clinical Studies, Drug Interaction, and more. Discuss any medical questions you have with your doctor or other health care provider. This is not all the information you need to know about this medicine for safe and effective use, and it does not take the place of talking to your doctor about your treatment.

The Package Insert is sometimes called Amondys 45 Prescribing Information (PI) or FDA label.

Amondys 45 J code

Amondys 45 J Code J1426 (10 mg, injection).

J codes are used for medicines that are not taken orally and include injections, inhalations, and chemotherapies. J codes are used for medical billing and are important for accurate and consistent coding for reimbursement purposes.

Your physician will need the Amondys 45 J-code when filling out forms for your treatment.

Storage

Store at 2°C to 8°C (36°F to 46°F). 

Do not freeze. Store in original carton until ready for use to protect from light.

Company

Amondys 45 manufacturer Sarepta Therapeutics, Inc. Cambridge, MA 02142 USA

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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