With the US Food and Drug Administration's approval of Alprolix in March, the hemophilia B market is set for a shake-up. Alprolix, developed by Cambridge-Massachusetts–based Biogen Idec, is the first long-lasting clotting factor to treat factor IX deficiency. The new drug is a factor IX molecule fused with the Fc domain of human immunoglobulin G1, which avoids lysosomal degradation and extends the factor's half-life. Patients with severe hemophilia only need to inject Alprolix prophylactically around once every 10 days, compared with existing products from Baxter (Rixubis) and Pfizer (BeneFix) that must be injected every 2 to 4 days. “This is a significant advance,” says Marion Koerper, medical advisor to the National Hemophilia Foundation and hematologist at the University of California, San Francisco. As current drugs take up to 20 minutes to prepare and administer, she explains, Alprolix is likely to sway patients and boost compliance. Biogen Idec has priced its new entry at par, on an annual basis, with the competition. Barclays Capital analysts forecast annual sales of $75 million for Alprolix this year, peaking at $581 million in 2020. But uptake may be gradual because patients and their clinicians are reluctant to move away from known treatments. And Biogen Idec may need to move fast to beat other long-lasting agents coming down the pike. Novo Nordisk's pegylated Factor IX N9-GP and CSL Behring's Factor IX-albumin fusion protein CSL654 are both in phase 3 trials.