(Adds analyst comment on biosimilar risks to Humira, AbbVie)
By Ransdell Pierson
July 8 (Reuters) - Amgen Inc's version of AbbVie Inc's Humira arthritis drug, the world's top-selling medicine, appears similar in potency and safety to the original product, U.S. Food and Drug Administration staff members said on Friday.
The assessment precedes an all-day meeting on Tuesday of an independent panel of medical advisers who will decide whether to recommend approval of ABP 501, Amgen's cheaper version of Humira. In two large Amgen studies, the Thousand Oaks, California-based company said it showed similar effectiveness to Humira.
In documents posted on the FDA's website, staff scientists said those trials suggested ABP 501 and Humira are "highly similar" in their safety, purity and potency in treating rheumatoid arthritis and plaque psoriasis.
The staff's briefing report said Amgen's data also supported use of ABP 501 against other diseases Humira treats.
Amgen stock rose 1.9 percent, while shares of suburban Chicago-based AbbVie advanced 1 percent, amid broad gains for the stock market.
Injectable biotech drugs like Humira are made in living cells and cannot be identical, so copies of them are called biosimilars.
Humira, with annual sales of $14 billion, delivers 60 percent of AbbVie's revenue. Like Amgen's Enbrel and Johnson & Johnson's Remicade, it blocks a protein called tumor necrosis factor.
Investors are nervous because Humira's main patent lapses in December, opening the drug up to potential competition from cheaper biosimilars being developed by companies that also include Coherus Biosciences Inc and Germany's Boehringer Ingelheim. Amgen, as the first to seek U.S. approval, could have the inside track to become the first to market.
AbbVie says numerous other patents will stave off the introduction of biosimilar forms of Humira until at least 2022, ensuring continued strong U.S. sales.
Any company introducing a biosimilar before resolving patent disputes with the maker of the original product risks facing triple damages from an unfavorable court ruling.
Morningstar analyst Damien Conover, however, said the first biosimilar of Humira would win U.S. approval and be available well before 2022, causing sales of the branded drug to fall about 5 percent in 2018 and 18 percent in 2019.
"There will be litigation back and forth, but we think these biosimilars will be launched and probably do more damage to Humira than (Wall Street) is expecting," Conover said.
Although Amgen has suggested it will introduce ABP 501 by 2018, Credit Suisse analyst Vamil Divan said he expected no Humira biosimilars in the United States until 2021 because of AbbVie's "broad patent estate."
Even as Amgen pushes its copy of Humira to market, it is fighting to fend off biosimilar competition for Enbrel. The same FDA advisory panel will decide on Wednesday whether to recommend Novartis AG's cheaper version of the drug, which brings Amgen annual U.S. sales of more than $5 billion.
The FDA in the past year has approved the first two U.S. biosimilars, including Novartis's version of Neupogen, an Amgen drug used to boost white blood cells. It has also approved a biosimilar form of Remicade developed by Celltrion Inc and Pfizer Inc.
(Reporting by Ransdell Pierson; Editing by Lisa Von Ahn)