UPDATE 2-Biogen says hemophilia-A drug met late-stage trial goal

* Biogen hemophilia A drug effective in trial

* Plans to file with U.S. regulators in first-half of '13

* Will file with European regulators after children's trial

* Results disappoint some; shares fall 4 percent at midday

(Updates with company comment, share price, details)

BOSTON, Oct 31 (Reuters) - Biogen Idec Inc said on Wednesday its experimental treatment for patients with hemophilia A, a disorder that inhibits coagulation of the blood, controlled bleeding with fewer treatments in a late-stage clinical trial.

About 30 percent of patients in one arm of the trial were able to go five days without requiring a new dose of the drug, which was, however, a lower percentage than some analysts had expected. Biogen's shares fell 4 percent in midday trading on Nasdaq.

Still, the data showed that those who took the Biogen's drug prophylactically required one to two injections per week, compared with an average of three to four treatments a week with existing therapies, a benefit Biogen argues patients will find compelling.

``Where people got the idea that we were going to get everyone out to five days is beyond me,'' said Dr. Glenn Pierce, Chief Medical Officer for Biogen's hemophilia program.

Patients who prophylactically took doses of the drug tailored to their own body make-up had an annualized bleed rate of 1.6, Biogen said, while those who took a fixed weekly dose had an annualized bleed rate of 3.6. By comparison, those who took the drug only in response to a bleed had an annual bleed rate of 33.6.

``Frankly,'' Pierce said, ``this is very positive data.''

It suggests that patients who currently treat themselves episodically could dramatically reduce their bleed rates by moving to a fixed weekly dosing. This would not give them the level of coverage conferred by individualized dosing, but could represent an attractive option for some patients.

Currently, about 65 percent of adult patients take hemophilia A d rugs on an as-needed basis in the United States, Pierce said, while most children take it prophylactically. In some European countries more than 80 percent take the drug prophylactically.

Biogen, best known for its multiple sclerosis drugs Avonex and Tysabri, said it plans to submit an application to market the hemophilia A drug with the U.S. Food and Drug Administration in the first half of 2013. It will file with European regulators after it completes a study of the drug in children.

Last month, Biogen and its partner, Swedish Orphan Biovitrum AB (Sobi), reported promising results of a trial of their drug to treat hemophilia B, a less common form of the disease.

Hemophilia A is caused by a lack, or insufficient amount of, the blood coagulation factor VIII. Patients with hemophilia B lack or have reduced levels of coagulation factor IX.

Biogen's drugs are designed to cut the number of infusions needed to control bleeding. Existing Factor VIII products must be taken as many as three to four times a week. Factor IX products must be taken intravenously two or three times a week.

In Biogen's latest study, known as A-LONG, 98 percent of bleeding episodes were controlled with one or two injections of its long-lasting Factor VIII drug.

The market for hemophilia A treatments is worth about $5 billion, according to Biogen, while the market for hemophilia B treatments is about $1 billion. If approved Biogen's hemophilia A treatment would compete with a variety of shorter-acting products, including Baxter International Inc's market-leading drug Advate.

There were no serious safety problems reported with the drug.

Biogen's shares were trading at $137.11 in midday trading. Earlier they fell as low as $136.98.

(Reporting By Toni Clarke; Editing by Alden Bentley, Gerald E. McCormick and Leslie Gevirtz)