CurrentmhnPolicy CP.PHAR.470

Clinical Policy: Casimersen (Amondys 45)

Defines medical necessity criteria, prior authorization and coverage requirements for Amondys 45 (casimersen) for patients with Duchenne muscular dystrophy amenable to exon 45 skipping; applies to commercial, HIM and Medicaid lines of business.

Policy Summary

Payermhn

PolicyClinical Policy: Casimersen (Amondys 45)

Policy CodePolicy CP.PHAR.470

Change TypeAnnual review updatesmaterial changes included

Effective DateFeb 25, 2021

Next Review DateN/A

Key ActionSubmit prior authorization with documentation confirming genetic testing for exon 45 skipping and recent ambulation, cardiac and pulmonary assessments; do not exceed 30 mg/kg/week.

SourceLink

POLICY UPDATE CHANGES

Added a step therapy bypass for Illinois HIM per IL HB 5395 (step therapy requirement does not apply for Illinois HIM requests as of 1/1/2026).

Updated Appendix C with new contraindication per prescribing information.

Added criterion that member has not previously received gene replacement therapy for DMD (e.g., Elevidys).

Added Agamree (vamorolone) to list of corticosteroids in Appendix B.

30 mg/kg/weekmaximum weekly dose

6 monthsapproval duration

≥ 300 m6MWT threshold

≥ 40%LVEF threshold

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Coverage Criteria for Casimersen (Amondys 45)

Initial Therapy

Covered when ALL of the following are met.

Initial Approval for DMD: 1. Diagnosis of Duchenne muscular dystrophy with a mutation amenable to exon 45 skipping confirmed by genetic testing; 2. Age ≤ 13 years at therapy initiation; 3. Prescribed by or in consultation with a neurologist; 4. Within the last 30 days, all of the following assessments: (a) ambulatory with 6-minute walk test (6MWT) ≥ 300 m; (b) left ventricular ejection fraction (LVEF) ≥ 40%; (c) predicted forced vital capacity (FVC) ≥ 50%; 5. Inadequate response despite adherent oral corticosteroid use (e.g., prednisone, deflazacort [Emflaza], Agamree) for ≥ 6 months unless contraindicated or not tolerated; 6. Amondys 45 prescribed concurrently with an oral corticosteroid unless contraindicated; 7. Not prescribed concurrently with other exon-skipping therapies (e.g., Exondys 51, Vyondys 53, Viltepso); 8. No prior gene replacement therapy for DMD (e.g., Elevidys); 9. Dose does not exceed 30 mg/kg per week.see nodes

Approval duration: 6 months

Continuation Therapy

Covered when ALL of the following are met.

Continued Therapy for DMD: 1. Currently receiving Amondys 45 for a DMD mutation amenable to exon 45 skipping or previously met initial approval criteria; 2. Member is responding as shown by one of the following: (a) within the last 6 months all of: 6MWT ≥ 300 m; LVEF ≥ 40%; predicted FVC ≥ 50% OR (b) member received the medication via another insurer and medical records demonstrate improved or stable LVEF and FVC within the last 6 months; 3. Neurologist assessment within the last 6 months; 4. Amondys 45 prescribed concurrently with an oral corticosteroid unless contraindicated; 5. Not prescribed concurrently with other exon-skipping therapies (e.g., Exondys 51, Vyondys 53, Viltepso); 6. No prior gene replacement therapy for DMD (e.g., Elevidys); 7. For dose increases, new dose does not exceed 30 mg/kg per week.see nodes

Approval duration: 6 months

Not Authorized Indications

Not authorized unless documented under off‑label use policies.

Non‑FDA Indications: Coverage is not authorized for non‑FDA approved indications unless there is sufficient documentation of efficacy and safety per the off‑label use policies (CP.CPA.09 for commercial, HIM.PA.154 for Health Insurance Marketplace, CP.PMN.53 for Medicaid) or evidence of coverage documents.

Requests for off‑label use should follow referenced off‑label policies.

Non‑FDA approved indications for Amondys 45 are not covered under this policy unless specific support is provided. Coverage for uses outside the FDA‑approved indication requires documentation of efficacy and safety consistent with the applicable off‑label use policies (see CP.CPA.09 for commercial, HIM.PA.154 for Health Insurance Marketplace, and CP.PMN.53 for Medicaid) or other evidence of coverage. In the absence of such documentation, requests for non‑FDA indications are not authorized.

Amondys 45 (casimersen) is indicated by the FDA for treatment of Duchenne muscular dystrophy in patients with a confirmed DMD mutation amenable to exon 45 skipping. Use of Amondys 45 for any other indication is considered not authorized under this policy unless the request is supported as an off‑label use per the referenced off‑label policies or other evidence of coverage; continued FDA approval for the indicated use was granted under accelerated approval based on increased dystrophin and clinical benefit remains to be verified.

Coding and Clinical Thresholds

HCPCS CodesHCPCS

J1426

Injection, casimersen, 10 mg

inv-07: 6-Minute Walk Test — ambulatory threshold

Threshold6-minute walk test (6MWT) distance ≥ 300 m (ambulatory) assessed within last 30 days for initial approval; assessed within last 6 months for continued therapy

Context in criteriaMember must be ambulatory (ability to walk with or without assistive devices; not wheelchair dependent) when meeting the 6MWT threshold

Use for continued therapyFor renewal, 6MWT ≥ 300 m must be documented within the last 6 months as evidence of response

inv-08: Left ventricular ejection fraction (LVEF) — cardiac function threshold

ThresholdLeft ventricular ejection fraction (LVEF) ≥ 40% (stable cardiac function required)

Assessment timing

Provider Actions, Prior Authorization and Step Therapy

Prior Authorization

Prior Authorization Required

Prior authorization is required for Amondys 45. Requests must include dosing information and do not exceed the maximum recommended dose of 30 mg/kg per week.

HCPCS J1426 (casimersen) — include dose and frequency
Approval duration: 6 months

Step Therapy

Corticosteroid Step Therapy

Step therapy requires inadequate response to an oral corticosteroid for ≥ 6 months unless corticosteroids are contraindicated or cause clinically significant adverse effects. For Illinois HIM requests, the corticosteroid step therapy requirement does not apply per IL HB 5395 (effective 1/1/2026).

Step therapy applies before initiating Amondys 45 unless contraindicated
IL HB 5395 bypass for Illinois HIM effective 01/01/2026

Background

Casimersen (Amondys 45) is an antisense oligonucleotide approved to treat Duchenne muscular dystrophy in patients with a confirmed DMD mutation amenable to exon 45 skipping. The FDA granted this indication under accelerated approval based on observed increases in dystrophin production in skeletal muscle; continued approval may be contingent on verification of clinical benefit in confirmatory trials. Providers must submit supporting clinical documentation when requesting coverage under the policy.

Definitions

inv-15: casimersen — Casimersen (Amondys 45) definition

Generic nameCasimersen

Brand nameAmondys 45

Drug classAntisense oligonucleotide

HCPCS billing code (per policy)J1426 — Injection, casimersen, 10 mg

inv-16: 6MWT — 6-minute walk test definition

Test name6-minute walk test (6MWT)

PurposeAssessment of ambulatory function (distance walked in 6 minutes) for DMD patients