May 7 (Reuters) - Privately held contract manufacturer Future Pak said on Tuesday it will sweeten its buyout offer for Vanda Pharmaceuticals to include contingent value rights, in addition to the proposed offer price of $7.25 to $7.75 per share in cash for the drugmaker.

The rights would provide additional benefits to Vanda shareholders if certain performance targets are met.

Future Pak said the revised offer includes up to $260 million of potential contingent value rights or CVR payments and represents up to $4.37 per share in additional value for Vanda.

Vanda did not immediately respond to a request for comment.

Shares of the drugmaker rose 6% to $5.14 in premarket trading. (Reporting by Bhanvi Satija in Bengaluru; Editing by Krishna Chandra Eluri)