Dec. 10 (Bloomberg) -- Reckitt Benckiser Plc, the British maker of Strepsils throat lozenges, agreed to purchase Adams Respiratory Therapeutics Inc. for $2.3 billion to gain Mucinex expectorants and Delsym cough medicine.

Reckitt will pay $60 in cash for each share of Chester, New Jersey-based Adams, the Slough, England-based company said today. That's 37 percent more than Adams' Dec. 7 closing price. The U.S. company's stock climbed to a record and Reckitt shares reached a seven-week high.

Adams's profit as a percentage of sales will more than double in the next three years, Reckitt Chief Executive Officer Bart Becht said on a conference call. Reckitt, the biggest maker of household cleaners, is bulking up in health by entering the U.S. market for over-the-counter remedies, almost two years after buying a Boots Group Plc division to gain Clearasil acne creams and Nurofen painkillers.

``It makes sense for Reckitt Benckiser to increase the over-the-counter business, which they started with the Boots unit,'' said Tom Gidley-Kitchin, an analyst at Charles Stanley in London with an ``accumulate'' recommendation on the shares.

The transaction probably will add to profit right away, excluding $60 million in reorganization costs, the U.K. company said. Adams Respiratory has annual sales of $332 million, which will probably double by 2012, Becht said.

Cough and cold treatments are ``one of the fastest-growing segments within the consumer health industry,'' said Frank Lopez, a sales executive at market-research firm Datamonitor Plc in London.

Margin Forecast

Adams Respiratory rose $15.62, or 36 percent, to $59.30 at 4 p.m. in Nasdaq Stock Market composite trading, the highest since the shares sold for $17 each in a July 2005 initial public offering.

Reckitt, whose cleanser brands include Lysol and Dettol, climbed 59 pence, or 2 percent, to 2,983 pence in London trading. They have gained almost 60 percent since Feb. 1 of last year, when the purchase of the Boots unit closed.

The transaction will increase revenue by more than 10 percent at Reckitt's health-care unit, according to Bloomberg calculations.

``Over a period of three years we will achieve operating margins in the mid-30'' percent range, Becht said, ``similar to what we achieved with the Boots unit.''

Reckitt doesn't have plans to launch its other brands in the U.S., he added.

Some analysts said Reckitt may have trouble making the acquisition pay off. Reckitt is paying more than six times sales, compared with 3.6 times when it bought Boots's health- care unit last year for 2 billion pounds ($4.1 billion).

``They are paying quite a premium,'' said Martin Deboo, an analyst at Investec Securities in London with a ``hold'' rating on shares of Reckitt. ``It will be a challenge to unlock value.'' Merrill Lynch & Co. advised Reckitt on the transaction, and Morgan Stanley was Adams Respiratory's adviser.

To contact the reporter on this story: Joram Kanner in Amsterdam at jkanner@bloomberg.net.

Last Updated: December 10, 2007 16:11 EST