Daniel Acker/Bloomberg News

Bristol-Myers Squibb agreed late on Saturday to buy Inhibitex, a maker of a hepatitis C treatment, for about $2.5 billion in cash, as major drug companies seek to bolster their pipelines with more profitable specialty products.

Under the deal, Bristol-Myers will pay $26 a share through a two-step merger, beginning with a tender offer. That represents a huge 163 percent premium over Inhibitex’s closing price Friday.

“The acquisition of Inhibitex builds on Bristol-Myers Squibb’s long history of discovering, developing and delivering innovative new medicines in virology and enriches our portfolio of investigational medicines for hepatitis C,” Lamberto Andreotti, chief executive of Bristol-Myers, said in a statement.

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Many big pharmaceutical companies have turned to mergers in recent years to plug holes in their drug pipelines, in large part to replace products that are set to face generic competition. Such companies are turning increasingly to smaller biopharmaceutical players developing specialized — and therefore hard to replicate — treatments.

In Inhibitex, Bristol-Myers will buy a company focused on antiviral products. Its main drug, INX-189, is an oral medicine being developed for hepatitis C that the company hopes will form the basis for simpler treatments of the disease.

Yet the deal is an expensive bet by Bristol-Myers, which says it expects the takeover to hurt its profitability for the next four years. Its earnings are expected to fall by 4 cents a share this year and 5 cents a share next year.

Inhibitex has not proved profitable lately, reporting annual losses from 2008 through 2010. For the quarter ended Sept. 30, the company, based in Alpharetta, Ga., reported a $5.3 million loss atop $1.3 million in revenue.

Bristol-Myers has said it plans to finance its bid by drawing upon its cash hoard. Shareholders owning about 17 percent of Inhibitex’s stock have already agreed to support the merger.

Bristol-Myers was advised by Citigroup and the law firm Kirkland & Ellis. Inhibitex was advised by Credit Suisse and the law firm Dechert.