April 25 (Reuters) - Investment firm Shareholder Capital sent a letter to drugmaker Vanda Pharmaceuticals' board on Thursday asking it to reconsider Future Pak's takeover offer.

On April 17, Vanda rejected contract manufacturer Future Pak's offer of $7.25 to $7.75 per share in cash, and adopted a shareholder rights plan to avert a hostile takeover attempt.

Shareholder asked in its letter, "on what basis did the Board reject Future Pak's offer, which values Vanda shares at nearly 2x their unaffected price."

The offer represents a 59-70% premium to Vanda's Wednesday closing price of $4.56.

Hedge fund manager Butler Hall Capital has also urged Vanda to form an independent special committee to engage with Future Pak over its takeover offer and run a full sales process.

Shareholder Capital, which owns 200,000 outstanding shares of Vanda, said Vanda's rejection of the offer reveals governance failures in the company.

Vanda did not immediately respond to a Reuters request for comment. (Reporting by Christy Santhosh in Bengaluru; Editing by Shinjini Ganguli)