Stiefel Laboratories Inc., a pharmaceutical firm specializing in dermatology, has bought one of Silicon Valley's biggest biotechnology companies, Connetics, for $17.50 a share --a 49 percent premium over the stock's price of $11.71 at the stock market's close Friday-- for an aggregate value of approximately $640 million.

"The combination of Stiefel and Connetics will create the world's premier dermatology company with a strong global presence in both branded and generic markets, dozens of marketed products and the most robust development pipeline in the industry. After the combination, Stiefel Laboratories, Inc. will have more than 3,500 employees worldwide, with more than 30 subsidiaries and sales in more than 100 countries."

Among the latest product in Connetics pipeline approved by the FDA is Verdeso(TM) (desonide) Foam, 0.05%, for the treatment of mild-to-moderate atopic dermatitis.

See more details of the merger from The Mercury News, and from Stiefel's and Connetics' press releases.