UPDATE 1-Eisai says Aricept's U.S. sales to more than halve

* Aims to offset Aricept’s U.S. patent expiry with new drugs

* Says to lift ROE to about 15 pct by 2011/12 (Adds details)

TOKYO, March 4 (Reuters) - Eisai Co 4523.T, Japan's No.4 drugmaker, said it expects annual U.S. sales of its flagship Alzheimer's drug Aricept to fall 60 percent in three years, hit by the expiration of the drug's patent later this year.

The drugmaker said in a statement it projects annual U.S. sales of Aricept to drop to $800 million in the year to March 2013 from an estimated $2 billion in the year to March 2011.

Even so, the company aims to offset the sales drop by introducing new drugs and capitalising on growth in Japan and China, it said.

“We have mapped out a plan to cope with the patent expiration, under which we will recover its impact by the fiscal year 2012 (to March 2013) and will return to a growth track by the fiscal year 2013,” Eisai President Haruo Naito told a news conference.

Eisai said in December last year it expects to launch four drugs in the United States in the financial year starting on April 1, including cancer drug Eribulin and sepsis medication Eritoran, and sees these four new items helping it offset the Aricept’s U.S. patent expiry.

Aricept, Eisai’s best-selling drug, generated 309 billion yen ($3.5 billion) in revenue, accounting for 39 percent of Eisai’s overall revenue in the year ended March 2009.

Eisai also said it aims to boost its return on equity to about 15 percent by the year to March 2012 from an estimated 9.7 percent in the current business year.

It is also plans to lift its earnings per share to about 228 yen by the same year from an estimated 141.4 yen this financial year, the company said in a statement. (Reporting by Chris Gallagher)