Biogen Inc. (NASDAQ:BIIB) shares tumbled as much as 8 percent Friday after sales of its multiple-sclerosis drug missed the analysts' consensus estimate for the first quarter. Reuters/Brian Snyder

The share price of Biogen Inc. (NASDAQ:BIIB) tumbled as much as 8 percent, to $395, Friday after sales of the biotechnology company’s multiple-sclerosis drug Tecfidera came in below the analysts’ consensus estimate for the first quarter. With a market capitalization of $95 billion, Biogen is the third-largest biotechnology firm in the world, behind Gilead Sciences Inc. ($154 billion) and Amgen Inc. ($127 billion).

Although Tecfidera revenue rose to $825 million in the first quarter from $506 million in the same period a year ago, its sales came in sharply below the consensus forecast of $931 million, according to Deutsche Bank.

Tecfidera revenue also dropped 10 percent sequentially, between the fourth quarter of last year and the first quarter of this quarter, as sales were partially affected by a comparatively strong U.S. dollar. In addition, there was one fewer shipping week in the U.S. and more discounting in the first quarter versus the fourth quarter, Biogen said.

Meanwhile, the company's total sales of multiple-sclerosis drugs came to $2.1 billion in the first quarter, up from $1.7 billion in the same period a year ago.

Biogen’s overall quarterly profit and sales fall last quarter also fell short of Wall Street estimates. The company reported first-quarter net income of $822.54 million, or earnings per share of $3.49, on revenue of $2.56 billion, compared with profit of $479.96 million, or EPS of $2.02, on sales of $2.13 billion a year earlier.

“In the first quarter, we continued to gain share in the MS market and we believe that our MS product portfolio is well positioned to provide patients the breadth of choices that they need,” Biogen CEO George A. Scangos said in a statement Friday.

Biogen announced last month its experimental drug aducanumab, or BIIB037, became the first Alzheimer’s treatment to significantly slow the cognitive decline in patients with early and mild forms of the disease, according to an early-stage study. The company said it plans to move the drug into a late-stage trial with more than 1,000 patients this year.