NEW YORK (TheStreet) -- Shares of Alexion Pharmaceuticals (ALXN) fell 9.9% to $151.87 in afternoon trading Wednesday after the company agreed to acquire Synageva Biopharma (GEVA) for $8.4 billion to widen its offering of rare disease treatments.
The cash-and-stock deal values Synageva at $230 a share based on Alexion's average closing price over the past nine days. This marks a 140% premium to Synageva's closing price of $95.87 on Tuesday.
Alexion agreed to pay $115 in cash and 0.6581 Alexion shares for every Synageva share.
The acquisition is an effort by Alexion to diversify from Soliris, the company's only marketed product. The company designed Soliris to treat two rare disorders: atypical hemolytic uremic syndrome and Paroxysmal nocturnal hemoglobinuria.
More than 10.1 million shares had changed hands as of 1:31 p.m., compared to the daily average volume of 1,241,030.
For more on this story, read Adam Feuerstein's in-depth coverage here.