Sanofi-Aventis CEO: We've Been Quick to Move

Sanofi-Aventis has been quick to move before its patents on bestselling products expired, said CEO Chris Viehbacher.

The French pharma company has expanded into other areas including vaccines, diabetes, animal health and emerging markets, including China where it bought a local medicine company to give it a distribution channel.

It also bought a biotech competitor, the American company Genzyme. The integration wasn't easy at first, he said.

"This is a transatlantic integration, French and American teams working together, big pharma and biotech. It wasn’t obvious," said the Sanofi CEO on CNBC's "Closing Bell" Thursday.

"It's difficult every time you bring two companies together," he added, "and when you bring smaller structures and bigger structures and different nationalities into the mix, you just have to make sure you spend a lot of time...with the teams and make sure it all went well. Over a year after the announcement of the deal it’s feeling natural and normal now."

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Update: An earlier version of this article mischaracterized where Genzyme is based.