NEWARK, JAN. 4 -- Swiss pharmaceutical giant F. Hoffman-La Roche and Co. AG announced today it has made a hostile $72-per-share cash offer for Sterling Drug Inc. in a deal estimated at $4.2 billion.

Hoffman-La Roche is best-known as the maker of Valium and is also a large chemical manufacturer. Sterling Drug's products include Bayer aspirin, Midol pain reliever and Lysol cleaner.

Officials from the companies were not available for comment.

Fritz Gerber, Hoffman-La Roche's chairman, made the offer in a letter to Sterling Chairman John M. Pietruski after Sterling executives spurned friendly merger talks.

"The business combination of Sterling Drug and Hoffmann-La Roche presents a unique opportunity for us, together, to join and build a global leader in our industries," Gerber wrote.

The $72-a-share offer was made after the close of New York Stock Exchange trading.

Sterling stock rose $1.75 Monday to $56.87 1/2 a share.

In his letter, Gerber said the board of Geneva-based Hoffmann-La Roche, which has U.S. operations based in Nutley, N.J., had unanimously authorized the offer to acquire all of New York-based Sterling's outstanding shares.

The cash offer is not contingent on financing or any other factors, Gerber said.