This is the open-label extension study of phase II ARGX-113-1802 to evaluate the long-term safety and efficacy of the subcutaneous formulation of efgartigimod in adults with CIDP.

Patients already stabilized on efgartigimod PH20 SC will also have the opportunity to participate in a sub study to explore less frequent dosing of efgartigimod PH20 SC.

Inclusion Criteria:

1. Ability to understand the requirements of the trial, provide written informed consent (including consent for the use and disclosure of research-related health information), willingness and ability to comply with the trial protocol procedures (including required trial visits) of this trial.

2. Male or female patient with one of the following options:

   • Have completed the Week-48 visit of Stage B of the ARGX-113-1802 trial and are considered to be eligible for treatment with efgartigimod PH20 SC; or
   • Have deteriorated during Stage B of the ARGX-113-1802 trial and are considered to be eligible for treatment with efgartigimod PH20 SC, or
   • Have been offered the participation in the OLE trial due to early termination of the ARGX-113-1802 trial (because sufficient events for the primary endpoint analysis of the that trial have been reached and it is stopped) and are considered to be eligible for treatment with efgartigimod PH20 SC treatment; or
   • Have completed the Week-48 visit of the previous cycle of the OLE trial and are considered to be eligible to continue with efgartigimod PH20 SC treatment.

3. Women of childbearing potential who have a negative urine pregnancy test at baseline before IMP administration.

4. Women of childbearing potential must use an acceptable method of contraception from signing the ICF until the date of the last administration of IMP.

Exclusion Criteria:

1. Week-48/ED visit in the ARGX-113-1802 trial or the Week-48 visit of the previous OLE participation occurred more than 14 days prior to SD1 of the OLE trial or the start of a new treatment cycle in the OLE trial and more than 21 days since the last dose of IMP.
2. Pregnant and lactating women and those intending to become pregnant during the trial.
3. Patients with clinical evidence of other significant serious disease or patients who underwent a recent or have a planned major surgery, or patients who (intend to) use prohibited medications (see protocol) and therapies during the trial, or any other reason which could confound the results of the trial or put the patient at undue risk.