Merck in $3.85B deal for Idenix

Merck is buying Idenix Pharmaceuticals, a company that is developing drugs to treat hepatitis C for about $3.85 billion, the companies said Monday.

Merck will pay $24.50 a share in cash.

The transaction has been approved by the boards of directors of both companies.

News of the deal sent Idenix shares soaring $16.73, more than 200%, to $23.96 in trading after the market opened Monday.

Idenix has three drugs in clinical development to treat the hepatitis C virus, known as HCV.

Merck's research and development portfolio includes several HCV medicines in development.