The FDA based its review on pivotal phase 3 data released in November showing patients treated with Nucala experienced an HES "flare-up" at only half the rate of those treated with placebo—28% versus 56%—over 32 weeks of therapy.
Nucala also showed significant improvements in several secondary endpoints in the study, which comprised 108 patients with severe HES. The risk of a first HES flare was 66% lower for patients treated with Nucala compared with placebo, and fatigue scores were also better in patients taking the GSK drug.
Nucala is already approved to treat severe eosinophilic asthma, and GSK plans to submit for a further approval in chronic rhinosinusitis with nasal polyps within the year.
Going first to the HES market will give Nucala a big step up over archrival Fasenra from AstraZeneca, which is pursuing an approval of its own.
In April 2019, AstraZeneca rolled out data from a 20-patient phase 2 trial showing Fasenra cut blood eosinophil counts by at least half in 90% of HES patients after 12 weeks of treatment. In comparison, only 30% of placebo patients saw the same result.
Fasenra isn't just chasing Nucala in clinical data; it's also a step behind in sales. In the second quarter, GSK's drug posted $310 million in global revenue compared with Fasenra's $227 million—but both drugs are growing at a rapid clip.
But GSK has other competitiors, too: The drugmaker is also hoping to take Nucala into a chronic rhinosinusitis space already occupied by Sanofi and Regeneron's world-beating IL-4/13 inhibitor Dupixent.
In April, phase 3 data showed Nucala added to standard of care cut the size of nasal polyps and the level of nasal obstruction after 52 weeks of treatment compared with standard of care alone in patients with chronic rhinosinusitis who had previously undergone surgery.
Dupixent scored its own nod in that indication back in June 2019, adding to the drug's blockbuster war chest.