Part B of the Phase 3b ADAPT NXT study in generalized myasthenia gravis (gMG; NCT04980495) investigated the long-term efficacy, safety, and tolerability of efgartigimod in participants with gMG receiving every-other-week (Q2W) or every-third-week (Q3W) dosing.

Efgartigimod, a human immunoglobulin G1 Fc fragment that blocks the neonatal Fc receptor, was well tolerated and efficacious when administered in fixed-cycles or Q2W dosing during Part A of ADAPT NXT.

Participants were randomized 3:1 to Q2W or fixed-cycles dosing of 10 mg/kg efgartigimod for 21 weeks in Part A. Fixed-cycles dosing involved 4 once-weekly infusions followed by a 4-week intertreatment period. In Part B, all participants received Q2W dosing during a 105-week extension. Participants could switch to Q3W dosing, depending on clinical assessment.

Sixty-five participants (of 69 in Part A [94.2%]) continued treatment in Part B; 57.8% (37/64) transitioned to Q3W dosing, and 59.5% (22/37) remained on Q3W dosing. Average Q3W treatment duration was 382 days. Myasthenia Gravis Activities of Daily Living (MG-ADL) total score improvements were sustained through Week 126. Overall, 81.2% (56/69) of participants experienced an MG-ADL improvement ≥5 points and 56.5% (39/69) achieved minimal symptom expression (MSE; MG-ADL score, 0-1) at any time during the study. In Part B, 51.6% (32/62) achieved MSE. Efgartigimod was well tolerated across dosing regimens; no new safety signals were observed. Data from the final analysis of ADAPT NXT will be presented at the conference.

Efgartigimod demonstrated sustained clinical benefits in patients with gMG during long-term treatment while remaining well tolerated across different dosing schedules.