Takeda Pharmaceutical Co. won approval from shareholders on Wednesday for its plan to purchase Irish drugmaker Shire Plc. for 46 billion pounds ($58 billion), the biggest-ever overseas acquisition by a Japanese company.

Takeda overcame opposition from some of its founding family members and other stakeholders who cited hefty debt to finance the deal, and will become the world's ninth-largest drugmaker with combined sales of about 2.8 trillion yen ($24.8 billion).

Nearly 90 percent of its shareholders approved the plan at an extraordinary meeting held in Osaka, Takeda said. Having already won regulatory approval in relevant countries including Japan, China and the United States, the company aims to complete the purchase by Jan. 8.

Takeda CEO Christophe Weber said in a statement he hopes to "create a more competitive, agile, highly profitable, and therefore more resilient company, poised to deliver highly innovative medicines and transformative care to patients around the world."

Japan's largest drugmaker is looking to add Shire's know-how in rare diseases including hemophilia to Takeda's core businesses of oncology, neuroscience and gastroenterology. Takeda also aims to increase its presence in the United States where Shire books more than 60 percent of its sales.

But the deal is also expected to increase Takeda's net interest-bearing debt to more than 5 trillion yen, about 10 times the amount before the acquisition, prompting some shareholders to describe it as too costly to pursue.

The opposing shareholders also said they are concerned about the reduction in earnings per share that will result from the new share issuance to finance the deal.

A group of shareholders had sought to vote down the takeover plan since their initial attempt to do so was rejected at a general shareholders' meeting in June.

At the shareholder meeting, an opponent of the takeover asked, "Isn't the acquisition a gamble?" But Weber said the deal would enable Takeda to strengthen its spending on research and development and gain competitiveness in the pharmaceutical industry.

The opponents include Kunio Takeda and Kazuhisa Takeda, founding family members and a former chairman, and former director of the drugmaker, respectively.

Kazuhisa Takeda said at a press conference at the Foreign Correspondents' Club of Japan in Tokyo earlier this week that the deal is too risky.

"It may be true that Takeda has not been successful in recent years to strengthen its new drugs...but I think Shire is not the answer," he said.

Shares of Takeda closed Wednesday up 1.1 percent from the previous day at 4,240 yen in Tokyo. They have lost more than 20 percent since Takeda announced in late March it was considering buying Shire.

Investors remain unable to accurately gauge the financial impact on Takeda from the deal, a market analyst said, adding, "The stock price will not recover unless (Takeda) shows a vision for growth."