The plaintiffs in the new case, filed late Thursday in U.S. District Court in Manhattan, include the California Public Employees' Retirement System (Calpers), the biggest U.S. public pension fund, the California State Teachers' Retirement System (Calstrs), and several mutual funds.

"Opting out" of securities class actions has become a growing trend, as some plaintiffs gamble they can do better by suing solo or in a small group instead of joining a larger case.

The plaintiffs in the new case said in September that they would not be part of the pending class action. The class action, led by the Teachers' Retirement System of Louisiana, grew out of lawsuits that started in 2004 following a study on the cardiovascular risks of Celebrex and Bextra.

Pfizer said it will fight the new case, as well as another opt-out case and the larger class action.

"The company believes these cases and the original class action lawsuit have no merit based on the undisputed facts in the record and the governing federal securities law," said Pfizer spokesman Chris Loder.

He said both drugs "were rigorously studied and tested" by the company and independent experts, and that the U.S. government, doctors, patients, and investors received accurate information on the risks and benefits of the medications.

Revenues from Celebrex and Bextra dropped by over $2 billion in the first nine months of 2005 after the safety concerns were made public, while Pfizer saw a $68.4 billion loss in stock market value between October 2004 and October 2005, according to allegations by investors.

In September 2009, Pfizer agreed to pay $2.3 billion to settle a U.S. Department of Justice probe into the marketing of drugs including Bextra.

Plaintiffs have opted out of past securities fraud class actions, including cases involving Countrywide Financial Corp and stemming from the collapse of WorldCom.

"Opt-outs are a major trend, probably reflecting the increased competition within the plaintiff's bar," said John Coffee, a law professor and securities law expert at Columbia University Law School. He said large institutional investors "can settle for more in cases in which they are not submerged in a huge class with smaller investors."

Other public pension funds in Thursday's lawsuit include the Teacher Retirement System of Texas, the Montana Board of Investments and the Arizona State Retirement System. Thrivent Financial for Lutherans and American Century Investment Management are also among the plaintiffs.

The complaint seeks compensatory and punitive damages, as well as interest and attorneys fees.

The plaintiffs are represented by Bernstein Litowitz Berger & Grossmann, a New York law firm that often leads class actions.

Other investors also have opted out of the Pfizer class action. Wolf Opportunity Fund Ltd and Okumus Capital LLC sued Pfizer on Wednesday, making similar allegations of fraud.

Matthew Siben, a lawyer for Wolf and Okumus with law firm Dietrich Siben Thorpe, did not respond to a request for comment Thursday.

Jay Eisenhofer, a lawyer for the lead plaintiff in the class action, declined to comment on the new cases.

The case is Montana Board of Investments, et al. v. Pfizer Inc., et al., U.S. District Court, Southern District of New York, No. 12-cv-9379 .

(Reporting By Nate Raymond; Editing by Martha Graybow and Tim Dobbyn)

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