Biogen Idec ( BIIB) reported a 27% increase in adjusted first-quarter earnings, but sales of its multiple sclerosis drug Tysabri fell short of Wall Street expectations.

The Cambridge, Mass-based biotech firm reported first-quarter net income of $244 million, or 84 cents a share, compared to net income of $163 million, or 54 cents a share in the year-earlier period.

On an adjusted basis, Biogen earned $1.05 a share, 4 cents better than the consensus estimate per Thomson Reuters.

First-quarter revenue rose 10% to $1.04 billion from $942.2 million one year ago, shy of the consensus forecast of $1.07 billion.

Worldwide sales of the multiple sclerosis drug Tysabri totaled $227 million in the first quarter, short of the consensus estimate of $246 million.

Approximately 2,200 new patients, or about 169 patients per week, began taking Tysabri in the first quarter, a bit lower than investors were expecting.

During the fourth quarter of 2008, Biogen said it was adding about 177 new Tysabri patients per week.

Last month, Biogen executies laid out plans to re-accelerate Tysabri patient growth, including new research into treatments that could potentially reverse the effects of PML. The company has also pointed to internal market research showing a large percentage of neurologists expect to increase use of Tysabri over the next six months while only a small percentage of doctors plan to prescribe less Tysabri.

Biogen shares Tysabri revenue with Irish drug maker Elan ( ELN). Biogen recognized $165 million in revenue from Tysabri in the first quarter.

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