Pfizer (PFE.US) is planning to raise at least $5 billion through a U.S. dollar corporate bond offering, with part of the proceeds earmarked to finance its recent acquisition of obesity drug developer Metsera Inc. (MTSR), according to sources familiar with the matter. The New York-based pharmaceutical giant intends to issue the bonds in up to seven tranches.

Insiders revealed that the longest-dated 40-year bonds are initially priced at a spread of approximately 1.25 percentage points above U.S. Treasury yields. The bond issuance was launched on Tuesday alongside eight other investment-grade corporate debt offerings. This follows a $26.3 billion financing day in the market, driven by Amazon's (AMZN.US) $15 billion investment-grade bond sale the previous day.

Pfizer secured the acquisition of Metsera after a competitive bidding process, with the total deal value reaching up to $10 billion. The transaction includes a contingent value right component, offering an additional $20.65 per share in cash payments. The bond proceeds will also be used for general corporate purposes and refinancing existing debt.