AstraZeneca’s Fasenra is already pressuring GlaxoSmithKline's Nucala in severe eosinophilic asthma, and new data could help set up a showdown between the two in another indication.

By week 12 of a phase 2 study in hypereosinophilic syndrome (HES), Fasenra cut patients' blood eosinophil counts by at least half, AstraZeneca showed with results published Thursday. Only 30% of patients taking placebo reached that mark. 

In patients with biopsies taken, results showed a “near-complete depletion” of eosinophils, the company said.

“We are encouraged by these trial results for Fasenra in hypereosinophilic syndrome and the data are potentially important given the limited treatment options for this debilitating disease,” Mene Pangalos, AstraZeneca’s EVP of pharma R&D, said in a statement.

AstraZeneca spokeswoman Abigail Bozarth said the estimated U.S. population affected by HES, a rare disease that can lead to fatal organ damage, is around 20,500, but the number could be higher. 

"Given the challenges in diagnosing the disease, it’s likely that number is actually higher," Bozarth said in an email. "The global prevalence of HES is currently unknown, primarily due to the rare nature of this group of diseases and difficulty in diagnosis."

But Fasenra’s positive showing could spell trouble for GSK’s Nucala, which is currently in phase 3 trials for HES treatment.

Both drugs—alongside Sanofi’s Dupixent—are in a heated severe asthma race after Fasenra and Dupixent entered the field in November 2017 and October 2018, respectively.

GSK’s Nucala, which was approved to treat severe eosinophilic asthma in late 2015, initially shrugged off its competition in the field but later admitted to being unprepared for Fasenra’s challenge to the throne.

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“If you go back 12 months ago, I think we were very much behind on several parameters in terms of the perception of Nucala versus Fasenra,” Luke Miels, GSK’s pharma chief, said on the company's third-quarter conference call in November.

One area in which GSK has admitted Fasenra has the upper hand is in dosing. Nucala requires an injection every four weeks, while Fasenra requires treatment every eight weeks—an advantage Miels said couldn’t be “neutralized.”

Across the pond, Fasenra received a nod from the National Institute of Health and Care Excellence (NICE) in January that allowed the drug to reach an expanded pool of patients in England and Wales. Initially, the English drug watchdog only recommended Fasenra in patients for whom Nucala was not appropriate, but the new backing helped Fasenra compete in a wider market.

RELATED: AstraZeneca’s Fasenra puts more pressure on GSK’s Nucala with expanded NICE backing

In 2018, Fasenra secured $218 million in U.S. sales compared with £341 million ($446.27 million) for Nucala.

As the competition in severe asthma stiffens, GSK said it was placing its hopes on an at-home injector that could help swing the tide back in its favor. However, both companies will also compete with Sanofi’s Dupixent, the newest entry into the field.

RELATED: Sanofi's Dupixent set for $2.5B in peak asthma sales after scoring winning label: analyst

After its October FDA approval, analysts estimated Dupixent would boost Sanofi’s sales by $2.5 billion through what one analyst called, “the Goldilocks of labels compared to rivals.” 

Dupixent also stands to benefit as the only eosinophilic asthma treatment that can be administered at home—a point of pride that GSK will challenge with the 2019 scheduled release of its at-home injector.