Casimersen

Pronunciation: KAS-i-MER-sen
Brand name: Amondys 45
Dosage form: intravenous infusion
Drug class: Miscellaneous uncategorized agents

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

What is Casimersen?

Casimersen (Amondys 45) 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. Casimersen works by targeting the exon 45 part of the dystrophin gene to help the body make an effective dystrophin protein, which improve muscle stability and may slow disease progression. This mutation will be confirmed through genetic testing before starting treatment.

Casimersen is administered as a once weekly intravenous infusion.

Casimersen brand name is Amondys 45 by Sarepta Therapeutics, Inc.

Casimersen FDA approval was granted for the treatment of Duchenne muscular dystrophy (DMD) with a specific genetic mutation in the DMD gene that is treatable with exon 45 skipping. FDA approval was based on its ability to increase dystrophin protein levels, a key component for muscle function. Casimersen's FDA approval is an accelerated approval, and continued approval may require further clinical studies to confirm its long-term benefits in slowing disease progression.

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.

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

How does casimersen 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.

Casimersen side effects

Common side effects

Common casimersen 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 casimersen patients in Study 1 (NCT02500381).

Related/similar drugs

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.

Casimersen may cause other serious side effects. Call your doctor at once if you have:

• Pink, brown, or red urine
• Foamy urine
• 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

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 interactons.

Casimersen Package Insert 

Review the Casimersen Package Insert (Amondys 45) 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 Casimersen Prescribing Information (PI) or FDA label.

Casimersen J code

Casimersen 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 casimersen 5 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

Casimersen manufacturer Sarepta Therapeutics, Inc. Cambridge, MA 02142 USA

Further information

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

Medical Disclaimer