Sales of AbbVie's biggest product, the rheumatoid arthritis injection Humira, narrowly missed analysts' estimates in the fourth quarter, sending the shares down 3.9 per cent in early trading.

Humira sales rose 11 per cent to $3.72 billion, its best-ever quarter, but just under the $3.73 billion average of analysts’ estimates. While the drug continues to grow, sales are expected to erode as cheaper alternatives, known as biosimilars, come on the market. The US Food and Drug Administration accepted Amgen’s application for a biosimilar version of Humira in January.

Net income rose to $1.52 billion, or 92 US cents a share, for the quarter, compared with a loss of $810 million, or 51 cents, a year ago.

Profit excluding one-time items was $1.13 a share, compared with analysts’ estimates of $1.12.

Biosimilars may arrive first in Europe, and AbbVie estimates competition from them will begin in late 2018. In the meantime, the company has been seeking to diversify away from Humira, which accounted for 63 per cent of sales in 2014.

Total revenue rose 17 per cent to $6.4 billion, matching analysts’ estimates of $6.37 billion.

AbbVie said its adjusted operating margin in 2015 widened by 6.1 percentage points from the previous year. – Bloomberg