PARIS ( TheStreet) -- Sanofi ( SNY), the French drugmaker, has reached an agreement in principle on the outlines of a deal to buy Genzyme ( GENZ), according to multiple reports.

The deal will include a contingent value right based on the performance of Genzyme's Lemtrada, a multiple sclerosis drug, Reuters reports, citing sources. A CVR gives shareholders an added benefit if an acquired company hits a future benchmark.

Sanofi and Genzyme, the U.S. biotechnology company, could reach a deal within a week or two, Reuters reports. Just last week, Sanofi said "significant differences" remained on the potential CVR.

Sanofi's offer of $69 a share, or $18.5 billion, for Genzyme ends on Feb. 15.

Sanofi and Genzyme disclosed earlier Monday in a regulatory filing that Sanofi has begun due diligence on Genyzme's books.

-- Written by Joseph Woelfel

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