Why? A lawsuit filed by Chris Larson of San Diego claims the $15.6 billion takeover by AstraZeneca would unfairly enrich MedImmune execs at the expense of shareholders.

The lawsuit, which was filed in a Maryland state court late last month, also claims that MedImmune execs are withholding key information shareholders need to evaluate whether the $58 per share offer from AstraZeneca is fairly priced.

MedImmune execs have access to private info on assets and the financial outlook that “makes it inherently unfair for them to pursue any transaction wherein they will reap disproportionate benefits to the exclusion of maximizing shareholder value,” the suit claims.

The two companies revealed the lawsuit in documents filed Tuesday with the Securities and Exchange Commission. MedImmune said in its filing that the lawsuit, which seeks class action status, was without merit and that it will “vigorously” defend itself.

MedImmune and AstraZeneca announced the deal on April 22, which at the time represented a 53 percent premium over MedImmune’s share price a few weeks earlier. A tender offer to shareholders is set to expire on May 31.

The deal will likely lead to huge paydays. CEO David Mott would receive more than $145 million from the cashing out of stock options and other payoffs if the deal closes. Wayne Hockmeyer, the chairman who founded the company, would be paid $59.7 million.

MedImmune had previously resisted several calls for it to look for a buyer, but it foundered in the months leading up to the sale. The company, which posted more than $1 billion in sales last year, saw its stock price sag after disappointing sales figures of its top selling drug, Synagis, and delays with a new version of the treatment for childhood respiratory problems.

Company officials said the decision to sell was based in part on investor pressure for a sale and the belief that it could be profitable for shareholders. Hockmeyer said at the time that the sale created “remarkable value for shareholders.”

Source: Associated Press[tags]AstraZeneca, MedImmune[/tags]