The FDA recently approved Biogen Idec's (NASDAQ:BIIB) Alprolix for the treatment of hemophilia B. The longer-lasting therapy's convenient dosing requirements may help it quickly dig into Pfizer's (NYSE:PFE) BeneFIX market share.

The Alprolix marketing team better step on the gas. Both Novo Nordisk (NYSE:NVO) and Australia's CSL Limited (NASDAQOTH:CSLLY) have similar therapies in development that could eat into Biogen's market share. Will Biogen sew up the hemophilia B market only to watch it quickly unravel ?

Big improvement
Hemophilia B is characterized by insufficient levels of factor 9, a protein involved in the clotting process. Patients require periodic transfusions to replace the missing protein throughout their lives. Treatment is inconvenient, expensive, and often painful due to irritation at the infusion site.

Alprolix differentiates itself from other factor 9 replacements by requiring less frequent infusions. Its half-life, or period between infusion and a 50% concentration reduction, is much longer than existing therapies, meaning that it is effective for longer. During the B-Long trials that led to the FDA's approval of Alprolix, Biogen's therapy had a half-life of 82 hours, compared to BeneFIX's 34 hours. The results suggest that many patients can cut the number of required infusions in half or better by switching to Biogen's therapy.

Reducing trips to the clinic and soreness around infusion sites ought to help Alprolix take market share from Pfizer's BeneFIX and other clotting factors. Last year, Pfizer recorded $832 million in BeneFIX sales, an increase of 8% from 2012. Another $832 million would boost Biogen's top line by 12%, although it's hard to know how well Alprolix's commercialization will go.

Short-lived supremacy
Biogen considers Alprolix the first significant advance for hemophilia B treatment in 17 years. The next improvement might come along much faster. Novo Nordisk has a long-acting factor 9 replacement candidate in late-stage development, N9-GP. During the Paradigm 2 study, investigators documented its half-life at 110 hours. Novo Nordisk expects to submit applications for N9-GP some time next year.

Australia's CSL Limited also has a next-generation Factor 9 replacement therapy in late-stage development. CSL954 demonstrated a 92 hour half-life, putting it about halfway between Biogen and Novo's offerings .

Comparing half-life figures is a convenient way to quantify one therapy's advantage over another, but you should be careful not to place too much significance on them. It's important to remember these were seperate trials, not head-to-head studies. Also, a longer half-life might not lead to commercial success on its own.

Swedish partners
Just how much Biogen Idec stands to keep from Alprolix sales is still an unknown. When Biogen acquired the therapy, it also inherited a complicated collaboration agreement with Swedish Orphan Biovitrum, or Sobi.

Sobi has the option to pay for final development and commercialization activities in Europe and nearby regions, then pay a double-digit royalty to Biogen on those sales. Sobi would also pay Biogen for a share of past development costs in the region. In return, Sobi would receive double-digit royalties from Biogen on sales outside of Sobi's territory.

Following Alprolix's approval in both Canada and the US, Sobi stated that it is waiting for completion of a required, ongoing pediatric study. If the results are favorable, Sobi has indicated that it plans to file for market authorization in the EU and nearby regions.

Final take
Sobi's intentions regarding its option will be clearer following the estimated completion date of the pediatric trial next February. Whatever happens in the EU, Alprolix sales from North America are likely to give Biogen a nice bump before the end of the year.

Looking further ahead, this next generation therapy might have enough potential to reach blockbuster status by dominating the Hemophilia B market. Biogen is likely to have the rest of this year, possibly longer, before competitors submit applications to regulators in major markets. Until we see more direct comparisons, just how much pressure they will eventually put on Alprolix sales is tough to estimate. Nonetheless, Biogen investors in particular will want to keep a close eye on this market and its potential.

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