Amgen Inc. on Tuesday began selling $2 billion in debt in a two-part sale that will be split evenly between 10- and 30-year bonds, which have been given high ratings by the major rating services.

The sale by the Thousand Oaks biotech includes $1 billion in 10-year notes and $1 billion in 30-year bonds, both expecting to yield 3.45 percentage points over U.S. Treasury bonds, according IFR, a Thomson Reuters service.

Moody’s Investors Service, which rates the senior notes at A3, expects proceeds from the offering to be used for refinance old debt and other general corporate purposes such as working capital and share repurchases. Standard & Poor’s, which has given the bonds its A+ rating, expect proceeds to be used mainly to refinance debt. Amgen itself has not made a public announcement about the sale.

The senior debt will contain a so-called poison put that would allow investors to sell the bonds back at 101 cents on the dollar if there is a change of control at the company, a person familiar with the sale told Bloomberg News.

Amgen shares closed up 65 cents, or 1 percent, to $57.71 in Nasdaq trading.