UPDATE 1-Biogen posts much smaller-than-expected sales of new Alzheimer's drug

(Adds details from release, background)

Oct 20 (Reuters) - Biogen Inc fell well short of Wall Street estimates for third-quarter sales of its Alzheimer's drug Aduhelm on Wednesday, as the drugmaker struggles to sell the treatment to hospitals and get insurers to cover it.

The company recorded $300,000 in sales of the drug, compared to analysts' average estimates of $10.79 million, according to Refinitiv data.

Biogen has pinned its hopes on Aduhelm, the first new treatment for the memory-robbing disease in nearly 20 years, as it wrestles with increased competition for its main revenue drivers.

However, the $56,000-a-year treatment is facing a slower-than-expected uptake.

Several commercial insurers are waiting for further direction from the U.S. Centers for Medicare & Medicaid Services (CMS) before covering the drug, while some large hospitals have declined to use it.

The CMS will give its initial opinion on whether it will cover Aduhelm's cost in January 2022, with a final decision expected in April.

Meanwhile, the U.S. Food and Drug Administration's approval of the treatment using the accelerated approval pathway has been heavily debated, with U.S. lawmakers last month seeking more information related to the approval.

Revenue in the quarter fell to $2.78 billion, from $3.38 billion a year earlier. (Reporting by Oishee Majumdar and Dania Nadeem in Bengaluru)