How Efgartigimod Targets gMG
Efgartigimod (Vyvgart) treats generalized myasthenia gravis (gMG) by reducing harmful autoantibodies that attack the neuromuscular junction. In gMG, an autoimmune response produces antibodies, mainly anti-acetylcholine receptor (AChR) or anti-muscle-specific kinase (MuSK) types, which block or destroy receptors needed for muscle contraction signals. This leads to muscle weakness and fatigue.[1]
Efgartigimod is a human IgG1 Fc fragment engineered to bind the neonatal Fc receptor (FcRn) with high affinity. FcRn normally recycles IgG antibodies, extending their half-life in circulation. By binding FcRn inside cells, efgartigimod blocks this recycling, accelerating the degradation of all IgG antibodies—including pathogenic ones—without affecting other immune cells or proteins.[2][3]
Treatment Process and Dosing
Administered as an intravenous infusion (10 mg/kg) weekly for 4 weeks per cycle, it lowers total IgG levels by 60-80% at peak, with selective reduction in anti-AChR antibodies up to 75-90%. Symptom improvement often starts within weeks, measured by MG-ADL scores (daily activities) and QMG scores (quantitative muscle tests). Cycles repeat every 4-12 weeks based on response.[1][4]
Clinical Evidence from Trials
In the ADAPT phase 3 trial, 68% of AChR-positive gMG patients on efgartigimod improved by ≥2 points on MG-ADL versus 30% on placebo (p<0.0001). MuSK-positive patients showed similar benefits in the ADAPT+ trial. Long-term data indicate sustained efficacy over multiple cycles with no loss of response.[4][5]
Who Responds Best and Limitations
Best for AChR-seropositive adults (about 80% of gMG cases); also approved for MuSK-positive. Not for AChR-negative patients without other autoantibodies. IgG levels rebound after each cycle, so ongoing treatment is needed. Common side effects include respiratory infections (10-20%) due to lowered IgG, but serious events are rare.[1][4]
How It Differs from Other gMG Drugs
Unlike acetylcholinesterase inhibitors (e.g., pyridostigmine) that boost signaling but don't address root autoimmunity, or rituximab (B-cell depleter), efgartigimod selectively clears antibodies faster without broad immunosuppression. Compared to complement inhibitors like ravulizumab, it targets the antibody source upstream.[3][6]
Sources
[1]: Vyvgart Prescribing Information (FDA)
[2]: Howard et al., Lancet Neurol 2021 (ADAPT trial)
[3]: DrugPatentWatch.com - Efgartigimod Mechanism
[4]: Muppidi et al., Neurology 2022 (ADAPT+)
[5]: Argenx Investor Presentation (long-term data)
[6]: Gilhus et al., Nat Rev Neurol 2019 (gMG therapies)