UPDATE 1-Biogen profit smashes estimates on Spinraza demand

(Adds details, forecast)

July 25 (Reuters) - Biogen Inc's second-quarter profit blew past estimates, driven by higher-than-expected demand for its recently approved spinal muscular atrophy (SMA) drug, Spinraza.

Shares of the drugmaker, which also raised its 2017 earnings and revenue forecast on Tuesday, were up 4.6 percent at $297.69 in premarket trading.

The U.S. Food and Drug Administration last December approved Spinraza for SMA, which is the leading genetic cause of death in infants.

The expensive drug, priced at $125,000 per injection in the first year of use, brought in sales of a whopping $203 million, compared with consensus estimates of $70 million, compiled by Evercore ISI.

Sales of Biogen's oral multiple sclerosis bestseller, Tecfidera, came in at $1.11 billion, just ahead of consensus estimates of $1.02 billion.

Excluding items, the drugmaker earned $5.04 per share, handsomely beating estimates of $4.41 per share, according to Thomson Reuters I/B/E/S estimates.

Total revenue rose to 6.4 percent to $3.08 billion in the second quarter ended June 30, ahead of analysts' estimates of $2.81 billion.

Net income attributable to the company fell to $862.8 million, or $4.07 per share, compared with $1.05 billion, or $4.79 per share, a year earlier, due to higher costs. (Reporting by Natalie Grover in Bengaluru; Editing by Arun Koyyur)