A Study to Assess the Long-term Safety and Efficacy of a Subcutaneous Formulation of Efgartigimod in Adults With Active Idiopathic Inflammatory Myopathy

Study Overview
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Brief Summary
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The purpose of this study is to measure the long-term safety and tolerability of efgartigimod PH20 SC in adult participants with IIM who previously participated in ARGX-113-2007. Secondary objectives include efficacy measures of efgartigimod PH20 SC in participants with IIM.

Official Title
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A Phase 3, Single-Arm, Multicenter, Open-label Extension of Study ARGX-113-2007 to Investigate the Long-term Safety, Tolerability, and Efficacy of Efgartigimod PH20 SC in Participants Aged 18 Years and Older With Active Idiopathic Inflammatory Myopathy

Conditions
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Myositis

Intervention / Treatment
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* Biological: EFG PH20 SC


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Has completed trial ARGX-113-2007 Being capable of providing signed informed consent and complying with protocol requirements Agrees to use contraceptive measures consistent with local regulations and women of childbearing potential must have a negative urine pregnancy test at baseline before receiving the investigational medicinal product Exclusion Criteria: Intention to have major surgery during the study period; or any other medical condition that has arisen since enrollment in study ARGX-113-2007, that in the investigator's opinion, would confound the results of the study or put the participant at undue risk Known hypersensitivity reaction to investigational medicinal product or 1 of its excipients Development of any malignancy, either new or recurrent, other than basal cell carcinoma of the skin, regardless of relatedness Permanent discontinuation of IMP in ARGX-113-2007, or met the permanent discontinuation criteria at the rollover visit Diagnosis with a deselected subtype of myositis based on the analysis of the phase 2 stage data in ARGX-113-2007, unless the investigator determines that the participant is benefiting from IMP as defined by a score of much better or moderately better on the 'Clinical Global Impression of Change' and 'Patient Global Impression of Change' assessments for at least 12 weeks, and that enrolling in the study is in the participant's best interest

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: EFG PH20 SC<br>participants receiving efgartigimod PH20 SC on top of background treatment | Biological: EFG PH20 SC<br>* Subcutaneous injection of efgartigimod coformulated with rHuPH20, a permeation enhancer<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Incidence treatment-emergent adverse events and adverse event of special interest |  | Up to 60 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Composite Glucocorticoid Toxicity Index (C-GTI) comprising the Aggregate Improvement Score (AIS) and the Cumulative Worsening Score (CWS) |  | Up to 52 weeks | 
| Prednisone dose reduction (average monthly dose) |  | Up to 52 weeks | 
| Proportion of participants who discontinue corticosteroids |  | Up to 52 weeks | 
| Total improvement score (TIS) | measured on a [0,100] scale. Higher scores represent improvement; zero indicates no improvement or worsening (from baseline). | Up to 52 weeks | 
| Proportion of TIS responders (minimal, moderate, major) |  | up to 52 weeks | 
| Individual core set measures (CSMs) of the TIS | measured on a [0,100] scale. Higher scores represent improvement; zero indicates no improvement or worsening (from baseline). | up to 52 weeks | 
| Percentage of participants with clinically inactive disease |  | up to 52 weeks | 
| Percentage of participants with remission, defined as a clinically inactive disease for at least 24 weeks |  | up to 52 weeks |