Argenx's subcutaneous efgartigimod matches IV sibling in phase 3, clearing path to FDA filing this year

Argenx’s subcutaneous formulation of the active ingredient in Vyvgart has hit the primary endpoint in a phase 3 trial, clearing the biotech to file for approval of a product it expects to become the most popular version of the autoimmune drug. 

The FDA approved Vyvgart for use in the treatment of generalized myasthenia gravis late last year. Sales of the intravenous formulation are expected to grow slowly this year, with analysts predicting revenues of around $100 million, but argenx has grown into a biotech with a $15 billion market capitalization on the assumption that fatter years are ahead. The subcutaneous formulation, which is a separate product from Vyvgart with a separate BLA, is key to that assumption.

Argenx took a big step toward adding a subcutaneous option on Tuesday with the delivery of top-line data from a trial that compared its investigational formulation to the approved intravenous product. At Day 29, the mean total IgG reduction from baseline was 66.4% in the subcutaneous cohort compared to 62.2% in the intravenous arm, suggesting the new formulation is at least as effective at changing levels of a biomarker that correlated to clinical benefit in earlier studies of Vyvgart.

The primary endpoint success, which was expected by analysts at Jefferies, was accompanied by hits on secondary endpoints. Almost 70% of recipients of the subcutaneous formulation were responders on the Myasthenia Gravis Activities of Daily Living. Argenx has previously said the endpoints aren’t powered and were included to support the commercial team, but it framed the outcome as a success.

In a brief summary of the safety data, argenx said the profile was consistent with the Vyvgart phase 3, adding that mild and moderate injection site reactions that resolved over time were the most common adverse events. 

Armed with the data, argenx plans to file for FDA approval of the subcutaneous formulation by the end of the year. The formulation is more convenient than the existing intravenous treatment, with delivery taking around one minute and home administration a potential option. 

Argenx developed the subcutaneous formulation by co-formulating its active ingredient with Halozyme’s rhuPH20 enzyme.