How Does Efgartigimod (Vyvgart) Work for CIDP Treatment?

Efgartigimod is a targeted therapy designed to treat Chronic Inflammatory Demyelinating Polyradiculoneuropathy (CIDP) by accelerating the removal of Immunoglobulin G (IgG) antibodies from the bloodstream ^[1]. Marketed in the United States for subcutaneous (under-the-skin) injection as VYVGART HYTRULO (efgartigimod alfa and hyaluronidase-qvfc), this medication works differently from standard first-line therapies ^[2]. Instead of broadly suppressing the immune system or delivering high doses of donor antibodies, efgartigimod blocks a specific cellular recycling process. This causes the body to naturally break down and clear away circulating IgG, including the antibodies that may be contributing to nerve damage ^[1][3].

The Role of IgG Antibodies in CIDP

CIDP is a complex, immune-mediated disorder where the immune system mistakenly attacks the protective myelin coating around peripheral nerves. While specific, disease-causing autoantibodies are only identified in a subset of patients, IgG antibodies are believed to play a significant role in nerve inflammation for many people with CIDP ^[4][5].

Normally, the body has a built-in recycling system to keep IgG antibody levels stable. A receptor called the neonatal Fc receptor (FcRn) acts like a rescue protein: it grabs onto circulating IgG antibodies before they can be broken down by the body’s cells and recycles them back into the bloodstream ^[1][3]. This process is why IgG antibodies persist in the body for a long time.

How Efgartigimod Intervenes (Mechanism of Action)

Efgartigimod is an FcRn antagonist, meaning it is designed to specifically block this rescue receptor. It competes directly with your natural IgG antibodies for the FcRn ^[1][3]. When the receptors are occupied by the drug, your natural antibodies cannot bind to them. Instead of being recycled back into the blood, they are sent for cellular breakdown and destroyed ^[1][3].

By preventing this recycling, efgartigimod can reduce the total amount of IgG in your blood by roughly 50% to 75%, depending on the dosing ^[3][6]. Because it lowers all IgG, it does not distinguish between potentially harmful antibodies contributing to nerve damage and the helpful, protective IgG antibodies your body makes to fight infections ^[7][8].

It is important to understand that efgartigimod is not a cure. Lowering IgG levels rapidly does not mean your nerves will heal immediately. Nerve repair is a slow process, and the reduction in IgG is temporary, meaning ongoing treatment is required to maintain the effect ^[3]. Furthermore, clinical response does not depend on proving you have one specific antibody, as the drug lowers the entire pool of IgG ^[7][8].

How It Differs From Standard Treatments

Standard treatments for CIDP approach the immune system differently:

• Corticosteroids (like prednisone): These are broad immunosuppressants that reduce inflammation across multiple immune pathways, which can lead to wide-ranging side effects over time ^[9].
• IVIG (Intravenous Immunoglobulin): This therapy delivers a high dose of pooled, donor-derived IgG. While its exact mechanisms are complex, it provides various immunomodulatory effects rather than specifically targeting antibody recycling ^[10][11].
• Plasma Exchange (Plasmapheresis): This procedure physically filters the blood to remove antibodies and other immune factors.

Unlike these therapies, efgartigimod does not directly target T cells, nor does it lower other types of antibodies (like IgA and IgM) in the same way ^[12][13]. However, because it substantially reduces protective IgG, it carries specific safety considerations that standard treatments may not.

Important Note on Transitioning: If you and your doctor decide to switch to efgartigimod, you should never stop IVIG or corticosteroids abruptly on your own. Stopping effective therapy can trigger a severe relapse, and corticosteroids require a medically supervised taper ^[14][15].

Safety Considerations: Infection and Vaccination

Because efgartigimod lowers protective IgG antibodies, it increases the risk of infections.

• Infection Risk: Patients must be monitored for signs of infection (such as fever, chills, persistent cough, or painful urination). If a serious infection occurs, treatment may need to be delayed until the infection resolves ^[16][17].
• Vaccinations: Immunization status should be reviewed before starting treatment. Because the drug lowers IgG, your immune response to non-live vaccines may be reduced ^[7][18]. Live or live-attenuated vaccines are generally not recommended during treatment ^[7][8].
• Other Risks: The medication can also cause hypersensitivity reactions (including rash or shortness of breath) and injection-site reactions ^[16][17].

What the Clinical Trials Show (The ADHERE Trial)

Efgartigimod was studied in adults with active or worsening CIDP (or those dependent on ongoing therapy) in a major clinical trial known as ADHERE ^[19][2].

• Initial Improvement (Open-Label Phase): In the first stage of the trial, all participants received weekly subcutaneous efgartigimod. Of the 322 participants, 214 (66%) achieved a confirmed, clinically meaningful improvement in their symptoms (such as improved grip strength or mobility scores) ^[2]. This represents the response rate in this specific trial phase, not a guarantee that every person with CIDP will improve.
• Preventing Relapse (Randomized Phase): Only the 214 patients who initially improved were moved to the next stage, where they were randomly assigned to either continue the medication or switch to a placebo. Continuing efgartigimod reduced the relative risk of a CIDP relapse (defined as confirmed clinical deterioration) by 61% compared to placebo ^[2]. Specifically, 28% (31 of 111) of the efgartigimod group relapsed, compared to 54% (59 of 110) of the placebo group ^[2].

The ADHERE trial demonstrated that efgartigimod is effective at preventing relapse in patients who have already shown they respond to the drug ^[2]. However, the trial did not directly compare efgartigimod to IVIG or corticosteroids, so there is no head-to-head evidence showing it is superior to standard care ^[20].