SUMMARY

• The company cannot recommend any practices, procedures, or usage that deviate from the approved labeling.
• Please refer to the local labeling for information on the appropriate use of IMAAVY in patients with generalized myasthenia gravis (gMG).
• A combined population PK (pharmacokinetic)/PD (pharmacodynamic) model which assessed total serum immunoglobulin G (IgG) reductions when switching from efgartigimod to IMAAVY is summarized below.¹ 

CLINICAL DATA

Population PK/PD Model Analysis

Neyens et al (2025)¹ predicted total IgG change when switching from efgartigimod to IMAAVY using a combined population PK/PD model.

Study Design/Methods

• IMAAVY inhibits IgG recycling dependent on the fraction of free FcRn receptor (FcRn_free) relative to its baseline value (FcRn0).
• Efgartigimod inhibits IgG recycling based on a sigmoidal model calculated by a maximum x-fold increase (EMax) and efgartigimod serum concentration relative to the concentration of 50% effect size (EC₅₀). 
• Dosing regimen was simulated to the following:   
  • IMAAVY: 30 mg/kg intravenous (IV) loading dose (LD) at week 0 followed by 15 mg/kg every 2 weeks (Q2W)
  • Efgartigimod: repeating cycles of 4 doses of 10 mg/kg IV every week (QW) followed by a 4 week off period
• The PK models for IMAAVY and efgartigimod were simulated in parallel, assuming no interaction on PK.
• The efgartigimod IgG model was adapted from an induction of IgG loss to an inhibition of IgG recycling which allowed the IgG models for both products to merge into one.

Results

Simulations

Switch at week 8 with IMAAVY 30 mg/kg LD

• Efgartigimod cycles (4 weeks on/4 weeks off) of 10 mg/kg QW followed by IMAAVY 30 mg/kg LD + 15 mg/kg Q2W was compared with de novo IMAAVY steady state 30 mg/kg LD + 15 mg/kg Q2W and with efgartigimod (4 weeks on/4 weeks off).
• The de novo initiation of IMAAVY IV 30 mg/kg LD + 15 mg/kg Q2W resulted in a initial IgG reduction of 72% at week 2 and then, alternated between 81% (odd weeks) and 67% (prior to next dose). 
• Efgartigimod cycles (4 weeks on/4 weeks off) resulted in IgG reductions of 65% and 24% at week 4 and week 8, respectively. 
• Switching to IMAAVY after 8 weeks of efgartigimod treatment resulted in >70% IgG reduction within 1 week and a 74% reduction at week 2 (See Figure: Switch Comparison at Week 8 between IMAAVY and Efgartigimod).  

Early Switch: Switch at week 4, without LD

• Four doses of efgartigimod of 10 mg/kg QW followed by IMAAVY 15 mg/kg Q2W was compared with de novo IMAAVY steady state 30 mg/kg LD + 15 mg/kg Q2W and with efgartigimod (4 weeks on/4 weeks off).¹  
• Switching from efgartigimod to IMAAVY 15 mg/kg Q2W resembled an IgG profile similar to IMAAVY steady-state (See Figure: Switch to IMAAVY 4 Weeks After Start of Last Efgartigimod Cycle by Dose). 
• No relevant interactions between IMAAVY and residual efgartigimod concentrations are expected based on the semi-mechanistic model which also predicted that IgG is not reduced below the levels of IMAAVY steady state. 

Delayed Switch: Switch at week 12, including LD

• Efgartigimod cycles (4 weeks on/4 weeks off) of 10 mg/kg QW followed by, IMAAVY 30 mg/kg LD + 15 mg/kg Q2W was compared with de novo IMAAVY steady state 30 mg/kg LD + 15 mg/kg Q2W.¹ 
• If switching to IMAAVY is delayed such as at week 12, when IgG levels return to baseline following the start of an efgartigimod cycle, the IgG profile post-switching matched that predicted after de novo initiation.
  • An IgG reduction of 71% occurred within 1 week after the switch. 

Literature Search

A literature search of MEDLINE^®, EMBASE^®, BIOSIS Previews^®, and DERWENT^® (and/or other resources, including internal/external databases) was conducted on 13 November 2025.