Last Updated: 2006-07-05 9:00:22 -0400 (Reuters Health)

TOKYO (Reuters) - Pfizer Inc. said on Wednesday it will launch its antidepressant drug Zoloft in Japan on Friday and expects annual sales to reach 48.2 billion yen ($420 million) within six years.

J-Zoloft, as the product will be called in Japan, will compete with GlaxoSmithKline Plc's Paxil, which accounts for about half of the nation's antidepressant market worth 100 billion yen.

Zoloft was first approved in England in 1990 and is available in about 110 countries. Global sales of the product came to $3.26 billion in 2005.

It has taken the U.S. pharmaceutical giant eight years to win approval for the treatment in Japan. It submitted an application to sell the product with the local regulators in March 1998.

"The reason why it took so long was that we needed to conduct additional tests and provide more data to the regulators," a spokesman for Pfizer's Japanese arm said.

In the United States, Pfizer is introducing a generic version of Zoloft, the company said last week. Hampered by the Japanese regulators' slow review process for new drugs and the high cost of clinical trials, many widely used treatments available elsewhere are not available in Japan.

Of the 88 top-selling drugs worldwide that have been launched since 1981, 28 have still not been approved in Japan, according to a report issued in February by the think-tank Office of Pharmaceutical Industry Research.

($1=114.88 Yen)