In a filing with the Securities and Exchange Commission, Alpharma calls the $37-a-share offer was inadequate and continues to explore all strategic alternatives, including a possible sale to King or another party for a higher price.

“We have received expressions of interest from multiple parties who contacted us following King’s public disclosure of its proposal or who our financial advisers solicited at our request,” Alpharma’s ceo says in a statement.

“We believe other offers or alternatives to the King offer may emerge from this process that will provide shareholders with greater value than $37 per share,” he continues, adding that Alpharma has entered into confidentiality agreements with “a number of these parties” who have begun due diligence.

Mitchell adds that Alpharma has already received “a written preliminary indication of interest for a business combination from a party that includes a per-share price in excess of the King offer of $37 per share.” At the same time, Alpharma invited King to participate in the auction process.

UPDATE: King later responded this way: “Our $37 per share cash tender offer, which is not conditioned on financing, is the only outstanding offer for Alpharma and would provide its shareholders with a 67 percent premium over Alpharma’s closing price on August 4, 2008, the date of our initial written offer. Given the uncertainty in the financial markets, we believe it is in the best interests of Alpharma stockholders to consummate our transaction as quickly as possible.”

Alpharma, however, contended that the King offer is “opportunistically timed” to take advantage of the upcoming regulatory review of Alpharma’s experimental pain drug Embeda. Trial resultsr, which received a priority review status from the FDA could affect Alpharma’s value and its negotiating power with potential buyers.

Last month, King offered to pay $33 a share for Alpharma, or $1.4 billion, and raised the price to $37 a share, or $1.6 billion, earlier this month, but also took the offer directly to shareholders (back story).