Merck says U.S. agency upholds Singulair patent

NEW YORK Dec 17 (Reuters) - Merck & Co (MRK.N) on Thursday said the U.S. Patent and Trademark Office has agreed that the patent on the company's $4.5 billion-a-year Singulair asthma drug is valid and enforceable.

The agency rendered its decision seven months after a new online community called Article One Partners LLC challenged the patent and asked the Patent Office to re-examine its validity.

Merck said the Patent Office, which ordered a reexamination on May 20, rendered its finding after the drugmaker defended the patent in response to the reexamination request.

"It states that they agree with our arguments and plan to terminate the re-examination of the Singulair patent," said Merck spokesman Ronald Rogers.

The agency is expected to make its finding official within two to three months, by issuing a required certificate of reexamination, Rogers said.

Should the patent have been invalidated, generic drugmakers could have begun selling cheaper versions of Singulair before the patent lapses in 2012. (Reporting by Ransdell Pierson; editing by Carol Bishopric)