Amgen on Tuesday reported fourth-quarter results that beat earnings expectations on a pro forma basis that excludes acquisition costs.

The Thousand Oaks drug maker reported net income of $1 billion ($1.33 a share) in the quarter ended Dec. 31, compared to $788 million ($1.01) for the same period a year earlier. Revenue rose 13 percent to $5 billion.

Analysts on average expected earnings of $1.68 on revenue of $4.8 billion, according to Thomson Financial Network.

The company cited higher research and development investments, as well as costs associated with absorbing Onyx Pharmaceuticals Inc. as reasons for the lower earnings. Amgen paid $10.4 billion to acquire the South San Francisco cancer-drug developer on Oct. 1.

Excluding the one-time cost of the acquisition, Amgen posted earnings of $1.4 billion ($1.82), which exceeded expectations.

The higher revenue figures were driven by an 11 percent increase in product sales, including $1.4 billion attributed to anemia drug Neupogen.

For the full fiscal year, Amgen reported net income of $5 billion ($6.64) compared to $4.3 billion ($5.52) for the prior fiscal year. Annual revenue rose 8 percent to $18.7 billion.

“Amgen delivered financially and strategically in 2013,” said Chief Executive Robert Bradway, in a statement. “We now have 10 innovative development programs with registration-enabling data expected by 2016, six biosimilars in development and expanded presence in more than 75 countries.”

Shares closed up $2.18, or 1.8 percent, to $120.70 on the Nasdaq.