AbbVie (ABBV) - Get Report  shares on Tuesday were gently higher as the North Chicago biopharma giant pushed forward with the sale of tens of billions of bonds to help finance the $63 billion acquisition of rival Allergan (AGN) - Get Report .

AbbVie's stock was trading up 1.5% at $86.95 after Bloomberg reported that the company was planning a $28 billion bond offering.

A bond deal of this size would be the largest of the year and possibly one of the top five of all time, the news service reported.

The sale is in 10 parts. A 30-year security is the longest portion of the sale and carries a yield that is 2.1 percentage points higher than that of U.S. Treasurys, a person familiar with the deal told Bloomberg.

Managing the bond sale are Bank of America (BAC) - Get Report , Morgan Stanley (MS) - Get Report and Barclays (BCS) - Get Report , according to Bloomberg.

Last week, Martin Baccardax reported that Allergan posted stronger-than-expected third-quarter earnings last Tuesday, and boosted its full-year revenue guidance, as the Botox maker said its $63 billion takeover by biopharmaceutical group AbbVie would close early next year.

AbbVie said in June that it will pay $188.24 each in cash and shares for Allergan's outstanding common stock, a 45% premium to the group's closing price on June 24, in a deal that would value the Dublin-based group at around $63 billion. AbbVie said the deal will add around 10% to the group's adjusted earnings in the first year.

AbbVie's Richard Gonzalez will continue as chairman and Chief executive officer, the company said, and its main headquarters will remain in North Chicago, Illinois. Allergan CEO Saunders will join the combined group's board when the deal is closed.

Earlier this month, AbbVie beat analysts' forecasts and nudged its guidance for the final three months of the year higher, even as sales of its top-selling arthritis drug Humira face some selling pressure.

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