The move could pressure rivals such as Pfizer Inc to lower prices for existing hemophilia treatments, which provide patients with life-saving infusions of a blood clotting agent, according to doctors and industry analysts.

Biogen last month won U.S. and Canadian approval for Alprolix to treat hemophilia B, the more rare form of the condition that affects about 4,000 people in the United States and about 25,000 worldwide.

"We think we have priced (Alprolix) to create parity with existing therapies on an annual cost of therapy basis," Tony Kingsley, Biogen's head of global commercial operations, told Reuters in a telephone interview.

Drug pricing in the U.S. market has come under new scrutiny as state governments and health insurers balk over the $84,000 cost of Sovaldi, a new hepatitis C drug from Gilead Sciences Inc. It is the first of several new drugs expected on the market over the next two years that are seen as a major breakthrough in treatment of the liver-destroying disease.

Treating two-thirds of the estimated 3.2 million U.S. hepatitis C patients with the drug could top $200 billion, according to some analysts.

The Biogen hemophilia drug targets a relatively minuscule patient population. But the U.S. biotechnology company, and its peers including Gilead, have seen their shares drop sharply in recent weeks as investors question how much they will be able to charge for novel medicines in the future.

Unlike in Europe and elsewhere, where price controls help keep healthcare costs down and drugs may be rejected outright if they are viewed as too expensive for the benefit they provide, the U.S. Food and Drug Administration is not allowed to take cost into consideration in approving new medicines, and no such price controls on what drugmakers may charge for their products exist.

Extremely high prices for lifesaving drugs for rare diseases and genetic disorders have come under less payer pressure because they treat so few patients, even though they must be taken for a lifetime. In addition, the premium pricing had long been perceived as necessary to encourage pharmaceutical companies to develop treatments for extremely rare diseases in order to make the payoff worth their while.

The recent pricing pressure has evolved as insurance companies and government health plans, such as Medicare and Medicaid, grapple with the skyrocketing expense of innovative new medicines that could be used by tens of thousands, or millions, of patients. They include therapies combining new cancer drugs that could cost $90,000 or more each for a course of treatment, and the hepatitis C drugs that promise a cure with few side effects.

FACTORS IN PRICING BIOGEN

Kingsley said Biogen had been discussing the pricing for its new hemophilia drug prior to the furor over Sovaldi. But it would appear that the company has taken public perception of the new medicine's cost into consideration. Biogen Chief Executive George Scangos had signaled earlier this year that if he believed Alprolix was likely to be perceived as more of an advance in convenience than efficacy, it would probably be priced on a par with existing treatments.

Biogen, which in the next few months expects a U.S. approval decision for another drug to treat the more common hemophilia A, set a price for Alprolix of $2.85 per international unit. That is more than double the price of about $1.19 per unit for Pfizer's Benefix, one of the most widely used treatments for the disorder. Other approved, older hemophilia B products include Rixubis from Baxter International Inc and Mononine from CSL Behring.

But while current drugs are typically needed about two to three times a week, Alprolix is taken once a week or every 10 days, Biogen said. The total annual cost can vary widely based on a patient's weight, the severity of their clotting deficiency and other factors.

Deutsche Bank estimates that Biogen's hemophilia products can reach annual sales of $1.2 billion by 2017.

"We think it's a meaningful advance in a market that hasn't seen a significant advance in a decade and a half," said Kingsley, adding that Alprolix should be available to patients early next month.

Hemophilia is a hereditary disorder that prevents blood from clotting properly due to lack of a clotting factor protein in the blood. Patients with more severe hemophilia require larger and more frequent doses of blood clotting factors. Worldwide, about one in 5,000 men are born with hemophilia A and one in 25,000 men are born with hemophilia B each year.

Denmark's Novo Nordisk is also developing a long-acting treatment for hemophilia B, and expects to file next year for regulatory approval.

Alprolix is a bioengineered version of the blood coagulation protein known as factor IX, which is needed for normal blood clotting. If not properly treated, hemophilia can lead to bleeding into joints and muscles that can cause stiffness, pain, severe joint damage, disability, and death.

Biogen developed the drug in partnership with Swedish Orphan Biovitrum ABN.

(Reporting by Bill Berkrot; Editing by Michele Gershberg, Bernard Orr)

By Bill Berkrot