By Liz Hoffman, Jonathan D. Rockoff and Dana Mattioli 

Endo International PLC has made a takeover bid for Salix Pharmaceuticals Ltd., seeking to upend Valeant Pharmaceuticals International Inc.'s roughly $10 billion agreement to buy the drug maker.

Endo offered to buy Salix for $175 a share in cash and stock. The offer, made in a letter to Salix's board on Wednesday compares with Valeant's agreement to pay $158 a share for Salix last month. Endo also would have to swallow a $356 million breakup fee, or roughly $5.50 per share, that would be owed to Valeant should Salix walk away from the deal.

The surprise move is the latest sign of the torrid pace of consolidation in the drug industry, which has recently been reshaped through a series of large tie-ups, many driven by tax considerations. Last year, $268 billion in pharmaceutical mergers were announced globally, more than double the volume in 2013, according to Dealogic. And 2015 is off to an even faster start, with $65 billion of transactions year to date, up from $39 billion over the same period in 2014.

Salix, which makes treatments for the millions of people suffering from stomach disorders, last year had been close to a deal to sell itself to Allergan Inc., which itself was being pursued by Valeant.

After Allergan walked away from those talks--and agreed to be bought by Actavis PLC--Salix sought another buyer. Endo was one of the suitors vying for Salix, but its bid of $150 a share in cash and stock fell short of Valeant's, according to people familiar with the matter.

It isn't clear why Endo didn't make a higher bid then.

When the two companies were in talks late last year, Allergan had offered to pay $175 a share for Salix--even after discovering an inventory glitch, according to a regulatory filing and a person familiar with the matter. That makes Valeant's deal for $158 a share look like a bargain, and may help explain why its shares surged on the agreement.

Shares of Endo and Salix were halted for trading Wednesday. Before the halt, Endo fell 1.1% to $88.01, while Salix rose 6.4% to $167.80. Valeant, in Toronto trading, dropped 3.3% to $247.10.

This isn't the first time Endo has taken on a spoiler role. Last year, it broke up Auxilium Pharmaceuticals Inc.'s deal to merge with QLT Inc., swooping in with a $2.6 billion to buy Auxilium.

Endo's latest move pits its Chief Executive, Rajiv de Silva, against his former mentor, Valeant CEO Michael Pearson. Both men were consultants at McKinsey & Co., and Mr. de Silva was one of Mr. Pearson's top lieutenants at Valeant, serving as the company's president and chief operating officer before leaving to take the helm at Endo in 2013.

Under Mr. de Silva, Endo has borrowed from some of Valeant's playbook as it remakes itself, reorganizing into separate operating units, unloading unwanted businesses, hunting for acquisitions and buying proven drugs in lucrative markets like skin treatments, instead of relying on risky investments in early-stage research. But Endo also sees itself as different from Valeant by, for instance, investing heavily in late-stage drug development that could yield organic growth.

Like Valeant had earlier, Endo used an acquisition--its 2014 purchase of Paladin Labs Inc.--to lower its taxes by relocating abroad. Buying Salix, however, would be a big bite for Endo, which has a market value of roughly $15 billion.

Salix has lately bounced from one possible deal to another. Last fall, around the time Allergan was considering buying the company, Salix called off a planned acquisition of a unit of a European drug company amid shareholder pushback and new regulations aimed at deterring such tax-driven deals, known as inversions.

In November, Salix disclosed a backlog of wholesaler inventory that suggested demand for its top drugs might not be as high as previously thought. Its CEO later resigned, and the company lowered its earnings guidance for the year.

The renewed competition for Salix highlights a recent surge in foreign takeovers of U.S. drug providers. Companies like Valeant, which is based in Canada and pays less than 5% of its profit in taxes, and Endo, incorporated in Ireland, have been on the takeover hunt in the U.S. of late. They are often able to outbid U.S. rivals, in part because of tax savings, deal makers say.

Raleigh, N.C.-based Salix sells a drug called Xifaxan that some analysts say could exceed $1 billion in yearly sales if the Food and Drug Administration approves it to treat diarrhea caused by irritable bowel syndrome. The company reported $1.1 billion in total revenue last year.

Write to Liz Hoffman at liz.hoffman@wsj.com, Jonathan D. Rockoff at Jonathan.Rockoff@wsj.com and Dana Mattioli at dana.mattioli@wsj.com

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