Safety issues for Pfizer's Dupixent rival may 'give prescribers pause'

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Despite showing “comparable” efficacy to the incumbent, Pfizer's abrocitinib comes with side effects that could hamper its uptake, Jefferies analyst Biren Amin wrote. (Tracy Staton)

Over the past year, Pfizer’s eczema hopeful has posted promising efficacy results from multiple phase 3 studies, building its case to challenge Sanofi and Regeneron’s Dupixent. But there’s a little something that could stand in its way: safety.

The JAK inhibitor, abrocitinib, has shown in multiple studies that it can clear patients’ skin and resolve eczema symptoms such as skin inflammation and itching, even logging a slight edge over Dupixent on an itch-related measure in one of the trials. But, despite showing “comparable” efficacy to the incumbent, it comes with side effects that, in the words of Jefferies analyst Biren Amin, could "give prescribers pause" and hamper its uptake.

In a full data set published in the journal JAMA Dermatology, investigators observed a drop in platelet counts for patients taking abrocitinib, with a median decrease of 26% in patients on the higher dose and 19% in patients taking the lower dose compared to less than 1% in the placebo group.

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RELATED: Pfizer's JAK inhibitor hits the mark in another phase 3 eczema trial

Although platelet levels rebounded toward baseline as the study went on, Amin flagged that the mechanism behind those platelet reductions is unknown and that the trial excluded patients who would be especially susceptible to that kind of side effect, namely those with platelet dysfunction, thrombocytopenia (low platelet count) or coagulopathy, a clotting disorder.

What’s more, nearly 2% of patients in the low-dose group reported serious infections, compared to 1.3% of the placebo group. Two patients in the high-dose group (1.3%) developed herpes zoster, or shingles.

AbbVie’s rheumatoid arthritis med Rinvoq—another JAK1 inhibitor—posted a slightly lower rate (1%) for both serious infections and shingles in a phase 3 study, but it still required a black box warning for serious infections, Amin pointed out in an investor note. AbbVie is also testing Rinvoq in atopic dermatitis.

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“Taken together, given the safety signals around concerns for JAK1i class, initial adoption of abrocitinib might be limited to severe patients or only be used as a short course of induction before switching patients to other therapies to reduce the exposure,” Amin wrote. The fact that abrocitinib is a daily pill versus a twice-monthly injection like Dupixent may not make up for the risk of infection.

For its part, Pfizer is focusing on efficacy: “Results from the second pivotal trial for abrocitinib reinforce the potential symptom relief it can offer those living with moderate to severe atopic dermatitis, including for itch—one of the most bothersome symptoms of AD,” said Michael Corbo, Ph.D., chief development officer of Pfizer’s inflammation and immunology unit.

“We are hopeful that these findings, should abrocitinib be approved, will translate into meaningful improvements for patients who face daily challenges with this disease,” Corbo added.

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