Biogen Idec closed the quarter with $1.4 billion in sales, a 10% lift compared to the same period last year. The sales growth came from established products Avonex, an injection for multiple sclerosis, which saw sales jump 13% compared to the prior-year quarter, to $746 million, and MS shot Tysabri, which posted a 9% increase vs. Q1 2012, to $312 million. Rituxan, co-marketed with Roche for use in oncology and rheumatology settings, saw sales ebb 7% vs. the year-ago period, to $265 million for the quarter.

The day’s results were tinged by news of four cases of the brain disease PML, progressive multifocal leukoencephalopathy, over 19 years, seen in patients taking an ex-US version of oral dimethyl fumarate. That’s the active ingredient in Tecfidera, or BG-12, the MS pill which received an FDA nod last month. In the past, the brain infection has also shown up in patients taking Tysabri.

Biogen execs told investors during the day’s earnings call that the PML cases should not diminish hopes for sales of Tecfidera. Among its reasons: these patients were not taking Tecfidera but a different form of dimethyl fumarate, one that has been available for many years in Germany for treating psoriasis. Moreover, the FDA knew about the cases before it approved Tecfidera.

A dent to the new pill’s safety profile could have implications for the launch, early feedback for which has suggested impressive uptake. Forty percent of neurologists polled on MM&M‘s behalf indicated that they had been waiting for the drug’s approval and were ready to begin administering it upon the FDA’s green light.