Japan's Astellas Pharma said Monday that it has agreed to buy U.S. drugmaker Iveric Bio for about $5.9 billion in its biggest acquisition, giving it access to a range of ophthalmology treatments.

The deal marks the fifth major overseas acquisition by Astellas, Japan's third biggest drugmaker by sales, since 2019, part of a push to shore up its pipeline as its main sellers lose patent protection.

It is the second-largest cross-border acquisition by a Japanese drugmaker in the past five years, according to Refinitiv data, following Takeda Pharmaceutical's $6 billion purchase of Nimbus Therapeutics' psoriasis drug unit announced in December.

And it comes on the heels of Kirin Holdings saying it would buy Australian vitamin-maker Blackmores for $1.2 billion.

New Jersey-based Iveric, formerly branded as Ophthotech, is focused on developing treatments for retinal diseases, which fits with Astellas' focus on blindness and regeneration therapies.

The Iveric deal gives it drug candidates to treat some 160 million people worldwide suffering from eye ailments, particularly in its home market of Japan, which has one of the world's fastest aging populations.

Iveric's key asset is avacincaptad pegol (ACP), currently in trials for treating geographic atrophy, the advanced stage of macular degeneration, a common cause of vision loss in the elderly.

ACP, branded as Zimura, targets the C5 protein suspected of causing the growth of scarring associated with the disease.

The U.S. Food and Drug Administration in February granted priority review of ACP, and if approved, the treatment could be commercialized by the end of this year.

Along with treatments for menopause symptoms and bladder cancer, Astellas is counting on ACP to make up for the loss of sales exclusivity of its mainstay prostate cancer drug Xtandi, chief executive Naoki Okamura said at a briefing.

"We believe that this is going to be the third pillar," said Okamura, who ascended to the top job last month.

Through Berry Merger Sub, a wholly owned subsidiary of Astellas U.S. Holding, the Japanese company agreed to acquire Iveric for $40 per share in cash, Astellas said in a release.

The price is a 22% premium to Iveric's $32.89 closing price on Friday.

Astellas has been aggressively chasing acquisitions, announcing deals in late 2019 to buy U.S. biotech Xyphos Biosciences for up to $665 million and Audentes Therapeutics for about $3 billion.

Its track record on deals has been mixed, as the company had to book big impairments on Audentes.

"This deal, however, is mainly about a soon-to-be approved asset, and seems less likely to generate impairment losses," Jefferies analysts said in a note on the Iveric acquisition.

Astellas will fund the Iveric purchase via short-term loans and commercial paper amounting to about ¥800 billion ($5.8 billion).

Astellas shares gained 2.2% in Tokyo trading, outperforming a 0.9% advance in the benchmark 225-issue Nikkei average.