The phase 3b ADAPT NXT study (NCT04980495) investigated the efficacy, safety, and tolerability of efgartigimod administered either every other week (Q2W) or in fixed-cycle dosing regimens.

Individualized fixed-cycle dosing of efgartigimod, a human immunoglobulin G1 Fc-fragment that blocks the neonatal Fc receptor, was well tolerated and efficacious in the ADAPT/ADAPT+ phase 3 trials in generalized myasthenia gravis (gMG).

Adult participants with anti-acetylcholine receptor antibody positive gMG were randomized 3:1 to Q2W or fixed-cycle (4 once-weekly infusions, 4 weeks between cycles) dosing of 10 mg/kg efgartigimod for a 21-week period in Part A. In Part B, participants in the fixed-cycle arm received one additional cycle of 4 once-weekly infusions of efgartigimod before switching to a Q2W regimen. All participants had an option to switch to every-three-weeks (Q3W) dosing in Part B, depending on clinical assessment.

Sixty-nine participants were treated (fixed cycle, n=17; Q2W, n=52) in Part A. Least squares mean (95% CI) of the change from baseline in Myasthenia Gravis Activities of Daily Living (MG-ADL) total score from Week 1-21 (primary endpoint) was -5.1 (-6.5 to -3.8) in the fixed-cycle arm and -4.6 (-5.4 to -3.8) in the Q2W arm; changes remained similar through Week 21.  Achievement of minimal symptom expression (MG-ADL score 0-1) was observed in 47.1% (n=8/17) and 44.2% (n=23/52) of participants in the fixed-cycle and Q2W arms, respectively. Efgartigimod was well tolerated; COVID-19, upper respiratory tract infection, and headache were the most common treatment-emergent adverse events. Clinical data analysis for Part B will be presented at the congress.  

The results of ADAPT NXT build upon previous studies and provide additional efgartigimod dosing approaches (fixed cycles and Q2W) to maintain clinical efficacy in participants with gMG.