Exhibit 4
Novartis | Novartis AG |
| Lichtstrasse 35 |
| CH 4056 Basel |
August 8, 2012
The undersigned hereby certifies that Dr. Martin Henrich and Knut Mager are authorized to execute Amendment No. 7 to Schedule 13D with respect to Idenix Pharmaceuticals, Inc., on behalf of Novartis AG.
| /s/ Peter Rupprecht |
| Name: Peter Rupprecht |
| Title: Senior Corporate Counsel |