It was not clear at press time which agencies have won in other markets.
The review, said to be worth US$600 million, was announced last October. It is believed to have involved incumbent agency Draftfcb, which held the company's media account in the US jointly with fellow Interpublic agency Initiative—which also held some of the business in Europe.
Brands under Merck include Claritin, Dr. Scholl's and Coppertone.
Media agencies contacted for this article refused to comment or could not be reached.