With its megamerger with Allergan in the books, AbbVie is focusing its growth on a stable of homegrown meds, including recent rheumatoid arthritis launch Rinvoq. Signs were looking good already—and an FDA rejection for Gilead Sciences' likely blockbuster rival could give AbbVie's med an even bigger leg up.

The FDA dropped a complete response letter on Gilead's JAK med filgotinib earlier this week, and it's likely to push that med's debut into 2022 at the earliest. That means Rinvoq has plenty of runway pad its lead in RA, Piper analysts said in a note to clients Wednesday. 

The agency requested more data from two ongoing clinical trials, MANTA and MANTA-RAy, that are assessing the effect of the 200-mg dose of JAK1 inhibitor filgotinib on sperm concentrations in rheumatoid arthritis patients. Both studies are fully enrolled, Gilead said, and expect top-line results in the first half of 2021.

The delay could give Rinvoq time to not only hone its edge in RA but potentially add to its haul in other indications, too, including atopic dermatitis, or eczema.

"With Rinvoq already off to a robust start in RA, we think this development has to make (AbbVie's) commercial efforts that much easier," Piper analysts wrote. 

RELATED: FDA rejects Gilead's would-be blockbuster filgotinib over toxicity concerns

Of course, filgotinib's flop represents more than one win for AbbVie: Besides the fact that analysts expected Gilead's drug to snare $3 billion per year in RA alone, AbbVie had bailed on a $1.4 billion filgotinib deal with Galapagos in 2015 to focus instead on Rinvoq. 

After AbbVie walked away, Gilead swooped in with its own $2 billion deal with Galapagos to develop filgotinib. Gilead upped the ante last year with a $5.1 billion expansion of its Galapagos partnership to access a broad swath of the biotech's pipeline.

Rinvoq sales have just been gearing up—$149 million in the second quarter—but AbbVie believes its most recently rheumatology launch is on its way to blockbusterland. Paired with another superstar launch, psoriasis med Skyrizi, the duo could skyrocket to a combined $20 billion in annual sales if AbbVie's dreams come true.

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As of June, Rinvoq had secured 15% of "in-play" market share in RA patients, CEO Rick Gonzalez told analysts on a July earning call, and the med could soon overtake megablockbuster Humira in terms of prescriptions for first-time users.

While Rinvoq posted $149 million in second-quarter sales, that figure topped the Street consensus of $110 million and put the drug on track to hit $600 million by year's end. 

And those sales are just in RA. AbbVie is pushing the drug through late-stage clinical trials in both eczema and ankylosing spondylitis, hoping it can snare as many indications as possible to pick up slack from Humira, which faces U.S. biosimilars beginning in 2023.

RELATED: AbbVie's Rinvoq scores pivotal trial win in eczema. But do dermatologists trust JAK inhibitors?

Eczema, in particular, could be lucrative for Rinvoq, but if the JAK inhibitor's three pivotal trials pay off with regulators, AbbVie would be forced to contend with Sanofi and Regeneron's blockbuster Dupixent. 

Part of that challenge would be the JAK inhibitors' classwide black box warning for serious infection, cancer and blood clots. Gilead actually touted filgotinib's safety profile as a major leg up over the rest of the JAK class before the FDA asked for more info on sperm count concerns.

"Despite the compelling efficacy results (potentially superior to Dupixent) and a consistent safety profile, we expect Rinvoq to capture only limited share in the first-line setting given its class labeling," SVB Leerink analyst Geoffrey Porges wrote to clients in July. "For most younger patients, Dupixent is still likely to be the first choice given its combined robust efficacy and remarkable safety."

Despite those challenges, Porges said Rinvoq could still secure a place as standard of care for second-line eczema patients who previously failed on a biologic like Dupixent. That position could mean about a $2 billion boost to Rinvoq's peak sales—a total of $5 billion per year by Porges' lights though significantly less than other estimates.