London-based GlaxoSmithKline announced that by year-end, it will cut 1,000 sales positions, and will be shifting its U.S. headquarters to Research Triangle Park, North Carolina, from Philadelphia.

The move won't affect any of the 1,500 employees in Philadelphia, said a company spokeswoman. Glaxo has 5,000 employees and 35 buildings in Research Triangle Park.

Glaxo’s CEO Andrew Witty last month said the company is struggling to adapt to a “significant transitional period'' as four best-selling medicines face cheaper generic copies and sales of the diabetes drug Avandia slow. Revenue in the U.S. dropped 13 percent last quarter.

In October 2007, Glaxo announced it would cut jobs in sales, manufacturing and research as part of a plan to save 700 million pounds ($1.12 billion dollars) a year by 2010. In June, Glaxo said it planned to eliminate about 350 jobs in research and development in the U.S., U.K. and Italy.

Glaxo is joining the list of pharmaceutical companies cutting sales positions in the U.S. - Pfizer Inc., Merck & Co., Schering-Plough Corp. and Wyeth have also announced paring the staff that visit doctors, take free samples and offer free lunches.

According to the drugmakers, their sales staff has fewer products to sell and doctors have less time for pitches.

In the past seven years, the total U.S. pharmaceutical sales force has doubled while the number of doctors has grown just 15 percent, according to a report this year by consulting firm ZS Associates.