Biogen (NASDAQ:BIIB) delivered its fourth-quarter earnings report on Thursday, showing revenue up 4% year-over-year to $3.67 billion. Adjusted income of $1.49 billion was up 6% year over year, but on a per-share basis, the growth was 19% because the biotech repurchased 23.6 million shares worth $5.87 billion over the course of 2019.

Sales of Biogen's top-selling multiple sclerosis drug, Tecfidera, increased 5% year over year in the fourth quarter, while revenues from Tysabri, another multiple sclerosis drug, rose 2%. Sales of its older interferon drugs for multiple sclerosis continued their decline of the last few years, falling 14%.

Rounding out its major drugs, spinal muscular atrophy drug Spinraza was the top-grower of the quarter with sales up 16%. But its growth rate is decelerating -- for the year, Spinraza sales were up 22% -- now that the drug must compete with Novartis' gene therapy Zolgensma. In addition, sales growth outside the U.S. has as slowed as the initial momentum from its launch has waned.

Doctor with her hand on a patient's shoulder

Image source: Getty Images.

For 2020, management expects revenue in a range of $14.0 billion to $14.3 billion, lower than the $14.38 billion Biogen brought in last year. Adjusted earnings per share are expected to fall between $31.50 and $33.50, again slightly lower than the $33.57 per share the drugmaker earned last year.

Biogen is currently in a fight over the patent for Tecfidera, and its guidance assumes no generics for it will be launched in 2020. The guidance also accounts for additional costs associated with the potential launch of its Alzheimer's disease drug aducanumab, assuming it gets approved by the Food and Drug Administration.