Biogen Idec ( BIIB - Get Report) reported an 18% drop in adjusted second-quarter earnings, impacted by a one-time payment related to a recent drug-licensing deal, but sales of its multiple sclerosis drug Tysabri topped Wall Street expectations.

The Cambridge, Mass-based biotech firm reported second-quarter net income of $143 million, or 49 cents a share, compared with net income of $207 million, or 70 cents a share, in the year-earlier period.

On an adjusted basis, Biogen earned 75 cents a share, below the 83 cents a share consensus estimate of analysts surveyed by Thomson Reuters. However, Biogen's recent $110 million payment to Acorda Therapeutics ( ACOR - Get Report) for ex-U.S. marketing rights to a multiple sclerosis drug isn't reflected in some analyst estimates.

Second-quarter revenue rose 10% to $1.1 billion from $1 billion a year ago, slightly ahead of the consensus forecast of $1.07 billion.

Worldwide sales of the multiple sclerosis drug Tysabri totaled $254 million in the second quarter, topping the consensus estimate of $242 million.

The company said 43,300 patients were being treated with Tysabri at the end of June, which translates into about 254 new patients added per week in the second quarter. That's a big jump from 169 patients per week added in the first quarter. Biogen executives said previously that more than 200 patients per week were starting Tysabri in March and April.

Late last month, Biogen executives reported that a 10th multiple sclerosis patient being treated with Tysabri was diagnosed with the serious brain infection progressive multifocal leukoencephalopathy, or PML.

Biogen shares Tysabri revenue with Irish drug maker Elan ( ELN). Biogen recognized $188 million in revenue from Tysabri in the quarter.

Second-quarter sales of the multiple sclerosis drug Avonex rose 12% to $591 million, while Biogen recorded $261 million in revenue for its portion of sales of the cancer drug Rituxan, co-marketed by Roche.

Biogen updated its 2009 financial guidance, saying adjusted earnings would be greater than $3.85 a share, which is above the current consensus of $3.82 a share

Biogen shares closed Wednesday at $46.67.

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