The sale is subject to clearance by European antitrust authorities.
The companies made the announcement in a joint statement dated July 30.
Merck anticipates completing the transaction before Merck's planned $41.1 billion merger with Schering-Plough Corp. The merger is expected to close in the fourth quarter.
In addition, Merck, Sanofi-Aventis and Schering-Plough have signed a call option agreement. This means that after the close of the Merck/Schering-Plough merger, Sanofi-Aventis will have the option to combine the Intervet/Schering-Plough Animal Health business with Merial to form an animal health joint venture that would be owned equally by itself and the new Merck.
Any formation of a new animal health joint venture with Sanofi-Aventis is subject to antitrust reviews in the U.S. and Europe.
Sanofi-Aventis is based in Paris, Merck is in Whitehouse Station, N.J., and Schering-Plough is in Kenilworth, N.J.