Argenx Scores Priority Review for Generalized Myasthenia Gravis Therapeutic

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The FDA granted argenx Priority Review status for the company’s Biologics License Application for SC efgartigimod for generalized myasthenia gravis (gMG). 

The drug is co-formulated with recombinant human hyaluronidase PH20 (rHuPH20), Halozyme’s Enhanze drug delivery system. Enhanze helps deliver biologics subcutaneously that are usually administered via intravenous infusion.

MG is a rare neuromuscular disease that is debilitating, chronic, and progressive. It is an autoimmune disease that can happen at any age but is most common in women before the age of 40 and after the age of 60 in men. It usually starts with weakness in the muscles that control the eyes and eyelids but often progresses to a severe, generalized form (gMG) that includes weakness of the head, neck, trunk, limb, and respiratory muscles. 

An argenx spokesperson told BioSpace, “Every person living with gMG experiences the disease in their own unique way, including how they manage their symptoms. Our hope in offering both the intravenous and subcutaneous formulation of efgartigimod is to provide patients more flexibility in how they individualize their treatment experience whether by route of administration or dosing schedule.”

The FDA’s target action date for the BLA is March 20, 2023.

Current Treatment Options for gMG Patients

Although there is no cure for gMG, most people improve with treatment, often entering remission. Treatments include cholinesterase inhibitors, such as Mestinon (pyridostigmine), corticosteroids such as prednisone and a range of immunosuppressants. This includes Salix Pharmaceuticals’ Azasan (azathioprine), Teva Pharmaceutical’s Neosar (cyclophosphamide), DAVA Pharmaceuticals’ Rheumatrex (methotrexate) and Astellas Pharma’s Prograf (tacrolimus).

Additional therapies include monoclonal antibodies such as Genentech and Biogen’s Rituxan (rituximab) and AstraZeneca/Alexion’s Soliris (eculizumab). Intravenous immunoglobulin therapy is also considered if symptoms become worse.

The MG market is a little small. According to Fortune Business Insights, the MG market is expected to reach about $2.03 billion by 2028.

The Phase III ADAPT-SC Trial Details

The BLA was built on data from the Phase III ADAPT-SC trial to determine the noninferiority of the pharmacodynamic (PD) effect of the subcutaneous formulation of SC efgartigimod compared with IV Vyvgart in adults with gMG. 

Vyvgart (efgartigimod alfa-fcab) is approved to treat gMG via IV infusion. It was approved for gMG by the FDA in March 2021.

Most patients in the study were positive for acetylcholine receptor (AChR) antibodies, but also included patients whose AChR antibodies were not detected.

The trial hit the primary endpoint of total IgG reduction from baseline at day 29. This was noninferior to Vyvgart. Patients receiving SC efgartigimod achieved a mean total IgG reduction of 66.4% from baseline by Day 29 compared to 62.2% with Vyvgart.

The drug’s safety profile was consistent with the previous Phase III ADAPT study. It was generally well-tolerated, with the most common side effects being site injection reactions, which is common with SC-dosed biologics.

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