Just days after D.C.-based Vanda Pharmaceuticals said it had received an unsolicited buyout offer from a U.K. drug company, a suitor Vanda had previously rejected has returned with a sweetened offer.

Future Pak, a Michigan-based contract manufacturing and packaging company in the pharmaceuticals industry, has raised its offer from $8.50 to $9 a share, valuing Vanda at as much as $524 million. Vanda rejected Future Pak’s original offer last month, saying it substantially undervalued the company.

Future Pak’s offer trumps that of Cambridge, U.K.-based Cycle Pharmaceuticals, which valued Vanda at about $446 million.

Vanda said it will review Future Pak’s new offer, along with the one received from Cycle Pharmaceuticals.

Vanda has two commercialized drugs: Hetlioz, which is used to treat sleeping disorders, and Fanapt, a treatment for schizophrenia. Fanapt recently won FDA approval for use as a treatment for bipolar disorder.

Vanda is developing treatments for jet lag, sea sickness and stage fright.