Dec. 7 (Bloomberg) -- Ranbaxy Laboratories Ltd. won tentative U.S. approval to sell a generic version of Aricept, Eisai Co.'s best-selling Alzheimer's disease treatment.

Ranbaxy, India's second-largest drugmaker, was given tentative approval to sell donepezil hydrochloride, or generic Aricept, in 5 and 10 milligram tablets, the Food and Drug Administration said on its Web site. The company, based in Gurgaon, outside New Delhi, will need final approval from the FDA before it can begin selling the drug. Eisai fell in Tokyo trading after the announcement.

``Eisai is not taking any action at this point as the approval is tentative,'' Kazuo Aoshima, a spokesman for the Tokyo-based company, said in a telephone interview.

Aricept is the world's best-selling Alzheimer's treatment. Sales of the drug, for which the U.S. patent expires in 2010, increased 18 percent to 73.5 billion yen ($661 million) in the three months ended Sept. 30.

Eisai fell 60 yen, or 1.3 percent, to 4,740 yen on the Tokyo Stock Exchange today. Ranbaxy shares rose as much as 11.45 rupees, or 2.9 percent, to 409.4 rupees on the Bombay Stock Exchange. The shares gained 1.2 percent to 402.6 rupees at 1:24 p.m. local time.

To contact the reporter on this story: Suresh Seshadri in Bangalore at sseshadri1@bloomberg.net.

Last Updated: December 7, 2007 03:15 EST