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Investigating a new treatment for active idiopathic inflammatory myopathy

A Phase 2/3, Randomized, Double-Blinded, Placebo-Controlled, Parallel-Group, 2-Arm, Multicenter, Operationally Seamless Study to Evaluate the Efficacy, Safety, Tolerability, Pharmacodynamics, Pharmacokinetics, and Immunogenicity of Efgartigimod PH20 SC in Participants Aged 18 Years and Older With Active Idiopathic Inflammatory Myopathy

Phase2; Phase3 Interventional argenx · NCT05523167

This study is testing a new treatment for adults with active idiopathic inflammatory myopathy to see if it helps them feel better compared to a placebo.

Quick facts

PhasePhase2; Phase3
Study typeInterventional
Enrollment240 (estimated)
Ages18 Years and up
SexAll
Sponsorargenx Industry-sponsored
Locations201 sites (Phoenix, Arizona and 200 other locations)
Trial IDNCT05523167 on ClinicalTrials.gov

What this trial studies

This study aims to evaluate the efficacy and safety of efgartigimod PH20 SC in adults diagnosed with active idiopathic inflammatory myopathy (IIM), including subtypes such as dermatomyositis and immune-mediated necrotizing myopathy. Participants will receive either the treatment or a placebo, and their response will be measured using the Total Improvement Score (TIS). The study is designed to provide insights into how well this new treatment works compared to no treatment.

Who should consider this trial

Good fit: Ideal candidates include adults with a confirmed diagnosis of active idiopathic inflammatory myopathy, particularly those with dermatomyositis, polymyositis, or immune-mediated necrotizing myopathy.

Not a fit: Patients who do not have a diagnosis of idiopathic inflammatory myopathy or those with inactive disease may not benefit from this study.

Why it matters

Potential benefit: If successful, this treatment could significantly improve outcomes for patients suffering from active idiopathic inflammatory myopathy.

How similar studies have performed: Other studies have explored treatments for idiopathic inflammatory myopathy, but the specific approach of using efgartigimod PH20 SC is novel.

Eligibility criteria

Show full inclusion / exclusion criteria 
Inclusion Criteria:

* Ability to consent in the jurisdiction in which the study is taking place and capable of giving signed informed consent.
* A definite or probable clinical diagnosis of idiopathic inflammatory myopathy (IIM)
* One of the following medical histories: Diagnosis of dermatomyositis (DM) or juvenile dermatomyositis (JDM), Diagnosis of polymyositis (PM) (including antisynthetase syndrome (ASyS)), Diagnosis of immune-mediated necrotizing myopathy (IMNM)
* Diagnosed with active disease as defined by the presence of at least 1 of the following criteria: Abnormal levels of at least 1 of the following enzymes: creatine kinase (CK), aldolase, lactate dehydrogenase, aspartate aminotransaminase (AST), alanine aminotransferase (ALT), based on central laboratory results; Electromyography demonstrating active disease within the past 3 months; Active dermatomyositis (DM) skin rash; Muscle biopsy indicative of active idiopathic inflammatory myopathy (IIM) in the past 3 months; Magnetic resonance imaging within the past 3 months indicative of active inflammation
* Muscle weakness
* Receiving a permitted background treatment for idiopathic inflammatory myopathy.
* Contraceptive use consistent with local regulations, where available, for individuals participating in clinical studies. Women of childbearing potential must have a negative serum pregnancy test during screening and a negative urine pregnancy test at baseline before receiving investigational medicinal product (IMP).

The full list of inclusion criteria can be found in the protocol.

Exclusion Criteria:

* A clinically significant active infection at screening
* A COVID-19 polymerase chain reaction (PCR)-positive test before enrollment
* Any other known autoimmune disease that, in the investigator's opinion, would interfere with an accurate assessment of clinical symptoms of idiopathic inflammatory myopathy (IIM) or put the patient at undue risk
* A history of malignancy unless considered cured by adequate treatment, with no evidence of recurrence for ≥ 3 years before the first administration of the investigational medicinal product (IMP). Adequately treated participants with the following cancers can be included at any time: Basal cell or squamous cell skin cancer ; Carcinoma in situ of the cervix; Carcinoma in situ of the breast; Incidental histological finding of prostate cancer
* Severe muscle damage
* Glucocorticoid-induced myopathy that the investigator considers the primary cause of muscle weakness or permanent weakness linked to a non-idiopathic inflammatory myopathy (IIM) cause
* Juvenile myositis (JDM) diagnosed \> 5 years from screening or juvenile myositis with extensive calcinosis or severe calcinosis.
* Uncontrolled interstitial lung disease or any other uncontrolled idiopathic inflammatory myopathy (IIM) manifestation that, in the opinion of the investigator, would be likely to require treatment with prohibited medication during the study
* Other inflammatory and noninflammatory myopathies: inclusion body myositis, overlap myositis), metabolic myopathies, muscle dystrophies or a family history of muscle dystrophy, drug-induced or endocrine induced myositis, and juvenile myositis (other than juvenile dermatomyositis (JDM))
* Clinically significant disease, recent major surgery or intends to have surgery during the study, or has any other condition in the opinion of the investigator that could confound the results of the trial or put the patient at undue risk
* Known hypersensitivity reaction to investigational medicinal product (IMP) or 1 of its excipients
* Received a live or live-attenuated vaccine less than 4 weeks before screening.
* Positive serum test at screening for active viral infection with any of the following conditions: Hepatitis B virus (HBV); Hepatitis C virus (HCV); HIV
* Participant has previously participated in an efgartigimod clinical trial and received at least 1 dose of investigational medicinal product (IMP).
* Participant is concurrently participating in any other clinical study, including a noninterventional study.
* Participant has a current or history (ie, within 12 months of screening) of alcohol, drug, or medication abuse.
* Participant is pregnant or lactating or intends to become pregnant during the study.
* Participant has severe renal impairment .
* Participant is institutionalized by a court or other governmental order or is in a dependent relationship with the sponsor or investigator.

The full list of exclusion criteria can be found in the protocol.

Where this trial is running

Phoenix, Arizona and 200 other locations

+151 more sites — see ClinicalTrials.gov for the full list.

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions Active Idiopathic Inflammatory MyopathyMyositisDermatomyositisPolymyositisImmune-Mediated Necrotizing MyopathyAntisynthetase Syndrome
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.