Biogen Idec’s first-quarter financials have revealed a 49.6% rise in profits as sales of the multiple sclerosis treatment Tysabri rose again, though at a slightly lower rate than analysts expected.

Net income came in at just under $244 million, while revenues climbed 10.0% to $1.04 billion. These rises were driven by Tysabri (natalizumab) which brought in $165 million, up 44%. Global sales of the drug, which is partnered with Ireland’s Elan Corp, reached $227 million, which is about $15-$20 million lower than most analyst estimates.

At the end of the quarter, around 40,000 people were on commercial and clinical Tysabri therapy worldwide, but Biogen noted that given the current economic environment, the number of patients receiving free Tysabri had increased in line with unemployment, which had a $6-$10 million impact on revenue.

Ian Hunter, an analyst at stockbroker Goodbody noted that there was a decline in infusions per patient over the quarter, which would suggest that some are taking ‘drug holidays’. This was thought to be not only because of safety concerns (five cases of the brain disease progressive multifocal leukoencephalopathy have been reported since July 2008) but also because “patients are stretching the time between treatments for financial reasons”.

Biogen also noted that the US Food and Drug Administration has approved its high titre process for the production of Tysabri, having received a similar approval from the European Medicines Agency in December. "We expect this new process to result in about a four-fold increase in yield," chief operating officer Bob Hamm said.

As for Biogen’s older MS drug Avonex (interferon beta-1a), sales climbed 4% to $555 million, helped by a 9.5% price increase during the quarter. The rheumatoid arthritis and cancer drug Rituxan (rituximab) also did well, and revenues, which come from Biogen's joint venture with Genentech, rose 13% to $279 million.

Chief executive James Mullen noted that the results were in line with expectations, saying that “the expansion of our global footprint in recent years is serving us well, particularly in the current environment”. He added that one-third of sales currently come from outside the USA, “a clear illustration of our success in capturing the greatest amount of value for our products worldwide”.