Efgartigimod (Vyvgart)

Efgartigimod is a first-in-class engineered antibody fragment — not a small molecule, and not a full monoclonal antibody — that treats generalized myasthenia gravis by clearing out a patient's own antibodies wholesale, a completely different mechanism from this site's other myasthenia gravis page, zilucoplan. FDA-approved in December 2021 on the strength of a real placebo-controlled Phase 3 trial, it has since expanded into a second disease entirely — a peripheral-nerve disorder called CIDP — and, as of May 2026, into gMG patients whose blood tests don't show the original trial's target antibody at all.

A different way to treat myasthenia gravis: clearing antibodies, not blocking complement

Efgartigimod (Vyvgart, argenx) is neither a small molecule nor a full monoclonal antibody — it's an engineered fragment of a human IgG1 antibody's Fc (crystallizable fragment) region, modified to bind the neonatal Fc receptor (FcRn) far more tightly than natural antibodies do. FcRn's ordinary job is to rescue circulating IgG antibodies from degradation and recycle them back into the bloodstream, which is why IgG normally persists for roughly three weeks rather than being cleared quickly like most proteins. By occupying FcRn, efgartigimod outcompetes a patient's own IgG — including the antibodies that attack the neuromuscular junction in generalized myasthenia gravis (gMG) — for that recycling, so more of it gets degraded instead of returned to circulation. That's a mechanistically different approach from zilucoplan, this site's other gMG page, which blocks complement protein C5 downstream of the antibody attack rather than clearing the antibodies themselves.

The ADAPT trial

The pivotal Phase 3 ADAPT trial (Howard JF Jr, Bril V, Vu T, et al., for the ADAPT Investigator Study Group, "Safety, efficacy, and tolerability of efgartigimod in patients with generalised myasthenia gravis (ADAPT): a multicentre, randomised, placebo-controlled, phase 3 trial," Lancet Neurol 2021;20(7):526-536, PMID 34146511, DOI 10.1016/S1474-4422(21)00159-9) enrolled 167 adults with gMG at 56 centers in 15 countries between September 2018 and November 2019, randomizing them to cyclical once-weekly IV efgartigimod (84 patients) or placebo (83 patients). Among patients positive for anti-acetylcholine-receptor (AChR) antibodies — the trial's primary population — 68% (44 of 65) responded on the MG-ADL activities-of-daily-living scale during the first treatment cycle, versus 30% (19 of 64) on placebo (odds ratio 4.95, 95% CI 2.21-11.53, p<0.0001), with many responders improving within the first two weeks of dosing.

From IV to subcutaneous, then a second disease: CIDP

The FDA approved Vyvgart on 17 December 2021 for adult, AChR-antibody-positive gMG — the first FcRn blocker approved for any disease. On 20 June 2023, the FDA approved a subcutaneous coformulation (efgartigimod alfa with recombinant hyaluronidase, branded Vyvgart Hytrulo) that patients or caregivers can self-inject in roughly 30-90 seconds, instead of an infusion-center visit for each weekly dose. A year later, on 21 June 2024, the FDA approved Vyvgart Hytrulo for a second, unrelated autoimmune disease: chronic inflammatory demyelinating polyneuropathy (CIDP), a disorder of the peripheral nerves rather than the neuromuscular junction. That approval rested on the ADHERE trial (Allen JA, Lin J, Basta I, et al., Lancet Neurol 2024;23(10):1013-1024, PMID 39304241, DOI: 10.1016/S1474-4422(24)00309-0) — an open-label lead-in enrolling 322 patients, of whom 221 responders were then rerandomized into a placebo-controlled withdrawal phase (111 continuing efgartigimod, 110 switched to placebo) — which found a 61% reduction in the risk of relapse for patients who continued on efgartigimod versus those switched to placebo (28% relapsed on efgartigimod vs 54% on placebo; hazard ratio 0.39, 95% CI 0.25-0.61), making efgartigimod the first FcRn blocker approved for CIDP.

The May 2026 expansion: every antibody type, not just one

ADAPT and Vyvgart's original gMG approval covered only patients who test positive for anti-AChR antibodies — the antibody subtype the pivotal trial enrolled. On 8 May 2026, the FDA expanded both Vyvgart and Vyvgart Hytrulo to cover adult gMG regardless of antibody serotype: anti-AChR-positive, anti-MuSK-positive, anti-LRP4-positive, and "triple seronegative" patients with no detectable antibody of any of those three kinds — making efgartigimod the first gMG treatment approved without a serotype restriction. That expansion rested on a dedicated trial, ADAPT SERON, run specifically in patients without detectable AChR antibodies, which met its primary endpoint of a clinically meaningful improvement in MG-ADL score against placebo at four weeks.

Current status

argenx markets Vyvgart and Vyvgart Hytrulo globally for gMG and CIDP; the company also has ongoing Phase 3 programs testing efgartigimod in myositis, primary immune thrombocytopenia and Sjögren's disease, none of which is an approved indication as of this review. The most common adverse reactions in trials were respiratory tract infections and urinary tract infections, both somewhat more frequent than with placebo, along with infusion-related reactions specific to the IV formulation; efgartigimod does not carry an FDA boxed warning. As a specialty immunology biologic prescribed and monitored by a treating neurologist, there is no wellness, bodybuilding or grey-market interest in efgartigimod that we could find.