The treatment was granted a Prescription Drug User Fee Act target action date of May 10, 2026.
The FDA accepted for priority review a supplemental biologics license application (sBLA) for intravenous (IV) efgartigimod alfa-fcab (Vyvgart; argenx) for the treatment of adults with acetylcholine receptor antibody (AChR-Ab) seronegative generalized myasthenia gravis (gMG). With this announcement, the treatment was granted a Prescription Drug User Fee Act target action date of May 10, 2026.1
IV efgartigimod is a first-in-class neonatal Fc receptor antagonist used to treat gMG—which causes the muscles to tire and weaken easily throughout the body—in adults who are positive for antibodies directed toward a protein called AChR. In December 2021, IV efgartigimod received its first FDA approval for the treatment of gMG in adults who are AChR antibody positive.1,2
According to the manufacturer’s news release, approximately 80% of those with gMG have detectable antibodies against the AChR in sera. These patients are diagnosed with AChR-Ab seropositive gMG, whereas the 20% that do not have detectable serum antibodies directed against AChR are referred to as AChR-Ab seronegative.1
The sBLA is supported by data from the phase 3 ADAPT SERON clinical trial (NCT06298552)3, a randomized, double-blind, placebo-controlled, multicenter study evaluating the safety and efficacy of IV efgartigimod in adults with AChR-Ab seronegative gMG across all 3 subtypes (muscle-specific tyrosine kinase-positive [MuSK+], low-density lipoprotein receptor-related protein-positive [LRP4+], and triple seronegative gMG) across North America, Europe, China, and the Middle East.
This trial enrolled 119 patients and was split into 2 parts. The first part was a randomized segment in which patients received 4 once-weekly infusions of IV efgartigimod or placebo, followed by a 5-week follow-up and primary analysis (part A). Next was an open-label extension in which participants receive 2 fixed cycles of 4 once-weekly IV efgartigimod infusions (4-week interval between cycles), and from cycle 3 onward, additional cycles could be started 1 week or more following the last administration of the previous cycle, based on clinical status (part B). Prior to randomization, all patients were on a stable dose of at least 1 gMG treatment, including acetylcholinesterase inhibitors, corticosteroids, or nonsteroidal immunosuppressive drugs.3,4
The primary end point of the trial was change in Myasthenia Gravis Activities of Daily Living (MG-ADL) total score from baseline to day 29 (part A). Other end points were measured using the Quantitative Myasthenia Gravis (QMG), Myasthenia Gravis Quality of Life-15 revised (MG-QoL 15r), Myasthenia Gravis Composite (MGC), and EQ-5D-5L VAS scales.3
According to the findings, ADAPT SERON met its primary end point (P = .0068) and demonstrated a statistically significant improvement in MG-ADL total score compared with placebo after 4 weeks. Additionally, in the overall population, the mean change from baseline in patients treated with IV efgartigimod was a clinically meaningful 3.35-point improvement in MG-ADL total score at the week 4 point. Improvements in MG-ADL and QMG scores were observed across subsequent treatment cycles in the overall population and in all patient subgroups, including MuSK+, LRP4+, and triple seronegative gMG.1
Generally, IV efgartigimod was observed to be well-tolerated with a safety profile consistent with the previously established profile in patients with AChR-Ab seropositive gMG and other indications. No new safety concerns were identified, according to argenx.1
Trial Name: A Phase 3 Study to Evaluate the Efficacy and Safety of Efgartigimod IV in Patients With Acetylcholine Receptor Binding Antibody Seronegative Generalized Myasthenia Gravis (ADAPT SERON)
ClinicalTrials.gov ID: NCT06298552
Sponsor: argenx
Completion Date (Estimated): June 2027
The manufacturer does not recommend IV efgartigimod if patients have a serious allergy to efgartigimod alfa or any of the other ingredients in the name brand. Additionally, IV efgartigimod may cause serious allergic reactions and a decrease in blood pressure that can lead to fainting.1
“Patients living with seronegative gMG continue to face limited treatment options, and there remains a significant need to meaningfully improve their lives. The FDA’s acceptance of our sBLA with Priority Review status reflects the potential of [IV efgartigimod] to address this need,” Luc Truyen, MD, PhD, chief medical officer of argenx, said in a news release. “This development brings us closer to expanding the use of [IV efgartigimod] in a broad spectrum of patients with myasthenia gravis. We look forward to continuing our dialogue with the FDA as they review our application.”1
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