On blockbuster path, Argenx's red-hot Vyvgart comes up short in thrombocytopenia trial

On a roll with Vyvgart—which is on its way to blockbuster sales in just its second year on the market for generalized myasthenia gravis (gMG)—argenx’s heat check in another indication has missed badly.

On Tuesday, the Dutch company revealed that its subcutaneous formulation of the drug, Vyvgart Hytrulo, has flunked primary and secondary endpoints in a phase 3 study in a rare bleeding disorder, primary immune thrombocytopenia (ITP). In the trial, patients on placebo experienced better blood clotting than those on Vyvgart Hytrulo.

It is the first setback for argenx and its broad ambitions for its lone commercial product. By 2025, the company still expects to be active with Vyvgart in 15 different immunoglobin G-mediated autoimmune indications, CEO Tim Van Hauwermeiren said on a conference call. 

“These are times when we really embrace who we are as a company—one that is grounded in both innovation but also humility,” Van Hauwermeiren said. “It is important we learn from each dataset as we navigate this new field of medicine.”

Analysts at ODDO BHF have dropped their target price on argenx from 600 euros to 550 euros. By mid-morning on Tuesday, argenx’s share price was down by 10%.

During the call, company officials were at a loss trying to explain the trial results, especially considering the success of intravenous infusions of Vyvgart in ITP patients in an earlier trial. In that phase 3 study, which read out last year, Vyvgart improved (PDF) the platelet levels of 21.8% of patients.

In the most recent trial, only 13.7% of those on Vyvgart Hytrulo experienced a sustained platelet count response compared to 16.2% of those on placebo.

“We knew it would be a challenge to enroll two large ITP studies in an overlapping fashion,” Van Hauwermeiren said. “So we were not surprised to get a heavily pre-treated population, which is more difficult to drive into response.”

Also vexing to argenx is the difference in placebo response in the first trial, which came to 5%. Argenx’s chief medical officer Luke Truyen noted during the call that “certain regions had a highly variable response on placebo.”  

The results stand in contrast to the immediate success of Vyvgart in gMG. A month ago, the company reported third-quarter sales at $329 million, which was up 151% year over year and 22% sequentially, bringing its total haul for the first nine months of the year to $816 million.

The company also announced during its quarterly call that it will use a priority review voucher to hasten an FDA decision on its submission for approval for Vyvgart to treat chronic inflammatory demyelinating polyneuropathy (CIDP).

Analysts at ODDO have pegged Vyvgart’s peak sales to reach $13.6 billion by 2035.