Evaluate long-term safety, tolerability, and efficacy of subcutaneous (SC) efgartigimod PH20 (coformulated with recombinant human hyaluronidase PH20) in patients with generalized myasthenia gravis (gMG) enrolled in the ADAPT-SC+ open-label extension study.

In ADAPT-SC, efgartigimod PH20 SC was shown to have noninferior total IgG reduction to efgartigimod IV (approved in US, Japan, and EU) resulting in similar clinical improvement in patients with gMG. Patients completing ADAPT-SC, or enrolled in ADAPT+, were eligible to participate in the ongoing open-label extension, ADAPT-SC+.

Efgartigimod PH20 SC 1000 mg was administered in cycles of 4 weekly injections. Subsequent cycles were initiated at least 28 days from the last dose based on clinical evaluation. Clinical efficacy was assessed utilizing the Myasthenia Gravis Activities of Daily Living (MG-ADL) scale.  

As of March 2022, 164 participants received ≥1 dose of efgartigimod PH20 SC. Patients received ~3 cycles over a mean (SD) study duration of 170 (59) days, resulting in 72 patient-years of observation. Adverse events (AEs) were predominantly mild to moderate. The most frequent AEs were injection site erythema (25.6%), headache (15.2%), and COVID-19 (11.6%). All injection site reactions (ISRs) were mild/moderate and did not lead to treatment discontinuation. ISRs typically occurred within 24 hours of administration, resolved spontaneously, and incidence decreased with subsequent cycles. Two deaths were reported (metastatic renal cancer and COVID-19); neither were deemed efgartigimod-related per investigator. Improvement from cycle baseline in MG-ADL total score (mean [SE] improvement at week 4: –4.0 [0.25]) was observed in cycle 1, with consistent and repeatable improvements seen in subsequent cycles. Speed of onset, durability, and repeatability of improvements in MG-ADL were similar to those with efgartigimod IV during ADAPT/ADAPT+.

Results suggest that treatment with multiple cycles of efgartigimod PH20 SC was well tolerated, with no new safety signals identified. Observed safety and efficacy profile was consistent with ADAPT/ADAPT+.