UPDATE 1-Forest's drug for Alzheimer's gets patent extension

* Gets full five years of patent term extension

* Patent to now expire on April 11, 2015

March 10 (Reuters) - Drugmaker Forest Laboratories Inc (FRX.N) said the patent term for its Alzheimer's treatment, Namenda, has been extended by the U.S. Patent and Trademark Office and the patent will now expire on April 11, 2015.

In the latest third quarter, Namenda sales were $240.9 million, or 24 percent of total revenue for Forest.

The patent was expected to expire on September 13, 2013, but the agency determined that the patent was entitled to the full five years of patent term extension, Forest said in a statement.

Forest has an exclusive license to the patent from German pharmaceutical company Merz Pharma and the two companies have filed patent litigation against generic manufacturers seeking approval to market their versions of Namenda.

Shares of Forest closed at $18.79 Monday on New York Stock Exchange. (Reporting by Jennifer Robin Raj in Bangalore; Editing by Anil D'Silva)