(Adds details from conference call, background; updates share price)
By Tamara Mathias and Caroline Humer
May 28 (Reuters) - BioMarin Pharmaceutical Inc said on Tuesday data from an early study of its gene therapy for hemophilia A appeared to show blood clotting protein levels were stable, three years after patients were given a one-time infusion of the drug.
The company is expected to price the drug, valoctocogene roxaparvovec, at over $1 million for a single dose, but investors are focused on whether the effects of the treatment will last long enough to command such a high price.
The data suggest the value of the drug is equivalent to five-year cost of standard treatment for hemophilia, which the company said averaged about $400,000 for adults, Chief Executive Officer Jean-Jacques Bienaime told analysts on a call.
That suggests a total value of $2 million a year.
Bienaime also said he believed payers, a group that includes insurers, employers, and the government, would not pay for more than five years.
Last week, Swiss drugmaker Novartis AG priced its one-time gene therapy for spinal muscular atrophy at $2.1 million, the highest price ever for a drug. The price was based on five-year cost for its rival treatment, Biogen's Spinraza, Bienaime noted.
Hemophilia A is a genetic bleeding disorder, affecting muscles, joints or other tissues, caused by missing or defective factor VIII, a clotting protein.
The company said median Factor VIII activity levels measured in patients at the end of three years were 19.9 international unit per deciliter.
"By three years post a one-time infusion of valoctocogene roxaparvovec, we anticipate we are nearing the plateau of expression," Hank Fuchs, president of Global Research and Development at BioMarin, said, adding that bleeding control could be maintained for at least eight years.
Shares of the company were volatile in premarket trading on Tuesday, and fell 1.9% to $87.33.
"We believe plateauing of declining Factor VIII is reassuring (and) the data appears stronger than what we or investors largely assumed," SVB Leerink analyst Joseph Schwartz said.
Separately, BioMarin said data from a group of patients in a late-stage study of the drug showed it met certain criteria, which will help it to apply for approval in the United States and Europe.
Eight patients in the group achieved Factor VIII levels of 40 international units per deciliter or more, at 23 to 26 weeks, meeting pre-specified criteria, the company said.
BioMarin said it plans to meet with U.S. and European regulators to review the data. (Reporting by Caroline Humer in New York and Tamara Mathias in Bengaluru; Editing by James Emmanuel and Shinjini Ganguli)