(Adds details from Biogen's letter, adds Aduhelm sales)
July 22 (Reuters) - Biogen Inc on Thursday said the approval of its Alzheimer's disease drug was based on extensive data as it seeks to quell concerns about the drug's effectiveness, while reporting $2 million in initial sales for the treatment.
The decision by the U.S. Food and Drug Administration to approve the drug, Aduhelm, despite its panel of outside experts recommending against it has drawn criticism from doctors and hospitals, with some saying they will not prescribe the treatment or have prescribed it very slowly.
The company's shares rose 1.3% to $327.44 in early trading, also boosted by Biogen raising its full-year revenue expectations.
"We welcome a formal review into the interactions between the FDA and Biogen on the path to the approval of aducanumab. A better understanding of the facts is good for everyone involved," Alfred Sandrock, head of research and development, said in an open letter addressed to the Alzheimer's disease community.
The company recorded $2 million in sales of the drug in the quarter, compared to analysts' average estimate of $3.23 million, according to IBES data from Refinitiv.
It expects modest revenue from Aduhelm this year, and expects it to ramp up thereafter.
Biogen now expects total sales of $10.65 billion to $10.85 billion this year, from its prior estimates of $10.45 billion to $10.75 billion.
The company earned $448.5 million, or $2.99 per share, in the second quarter ended June 30, down from $1.54 billion, or $9.59 per share, a year earlier. (Reporting by Manas Mishra in Bengaluru; Editing by Sriraj Kalluvila)