argenx has reported positive results from the Phase III ADAPT clinical trial of efgartigimod in adults with generalised myasthenia gravis (gMG).

Efgartigimod is an investigational antibody fragment that can potentially lower disease-causing immunoglobulin G (IgG) antibodies and inhibit the IgG recycling process.

It attaches to the neonatal Fc receptor (FcRn), which is important for preventing the degradation of IgG antibodies. If approved, efgartigimod would be the first authorised FcRn antagonist.

The global, randomised, double-blind, placebo-controlled, multi-centre ADAPT trial assessed the safety and efficacy of the drug in 167 patients across North America, Europe and Japan.

Participants received efgartigimod or placebo over 26 weeks.

The primary endpoint was the number of acetylcholine receptor-antibody positive (AChR-Ab+) patients who experienced a response on the Myasthenia Gravis Activities of Daily Living (MG-ADL) score.

The MG-ADL response was determined as a minimum of a two-point improvement for at least four consecutive weeks.

The primary endpoint was met with significantly more AChR-Ab+ subjects responding on the MG-ADL score after treatment with efgartigimod versus placebo. Nearly 67% of patients treated with efgartigimod achieved a response compared to 29.7% on placebo.

Furthermore, 40% of participants in the efgartigimod arm showed minimal symptom expression determined as MG-ADL scores of zero (symptom free) or one, versus 11.1% in the placebo arm.

Among AChR-Ab+ responders, 84.1% had clinically meaningful improvement on the MG-ADL score in the initial two weeks of treatment.

The company added that the safety profile of efgartigimod was similar to that of placebo.

argenx chief medical officer Wim Parys said: “Efgartigimod is currently under review with the FDA for the treatment of gMG, and if approved, we look forward to bringing this therapy to MG patients who are in great need of new treatment options.”

After completing the ADAPT trial, 90% of subjects moved to an ongoing three-year open-label extension study, named ADAPT-plus, which is assessing the long-term safety and tolerability of the drug.

A total of at least 118 patients have received efgartigimod therapy for 12 months or more across the ADAPT and ADAPT-plus trials.