Biogen (BIIB - Get Report) said adjusted profit rose in the first quarter on a small increase in total revenue. Sales of the biotech company's multiple sclerosis drugs remain flat but the commercial debut of a new spine disease drug, Spinraza, outperformed expectations.

The Cambridge, Mass.-based biotech firm did not make any changes to its financial guidance for the year.

Biogen shares closed at $286.89 Tuesday, up $10.03, or 3.62%.

The FDA approved Spinraza in late December as the first treatment for spinal muscular atrophy (SMA), a rare, genetic condition affecting children that causes the loss of motor neurons in the spinal cord and lower brain stem, resulting in progressive loss of muscle function.

In the first full quarter of its commercial launch, Biogen said Spinraza sales totaled $47 million, beating handily Street consensus expectations that ranged from $15-17 million, depending on the source.

"We are encouraged by the progress we made launching Spinraza in the U.S., and, following the positive CHMP opinion, we are ramping up pre-launch activities in Europe," said Biogen CEO Michel Vounatsos, in a statement.

On its conference call, Biogen said less than $10 million of Spinraza's sales in the quarter came from wholesaler inventory stocking.

Spinraza's sales in the March quarter account for a little more than a rounding error to Biogen's total first-quarter revenue of $2.8 billion, but the drug represents the company's primary future growth driver given the weakening demand for its core multiple sclerosis drugs.

Sales of Tecfidera, Biogen's biggest multiple sclerosis drug, were $958 million in the quarter, 1% higher than the prior year.

Overall, sales of the company's multiple sclerosis drugs rose 3% year over year, which Vounatsos described as "stable." Biogen expects the launch of Roche's new multiple sclerosis drug Ocrevus to have a negative impact on its drugs.

Total revenue of $2.8 billion in the first quarter was 3% higher than the prior year, 8% higher if sales of hemophilia drugs, spun out into a separate company, are excluded.

On an adjusted basis, Biogen net income totaled $1.12 billion, or $5.20 per share, in the first quarter. That compares to adjusted net income of $1.05 billion, or $4.79 per share, in the first quarter of 2016.

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