More than a half-dozen of the top class action plaintiffs firms in the country have spent years pressing securities claims related to a joint effort by Pfizer’s Wyeth unit and Irish biotech company Elan to develop a treatment for Alzheimer’s disease. Six months ago a federal judge in New York threw out a consolidated class action alleging that Elan misrepresented the status of clinical trials for the drug. Now Pfizer has cleared the decks of the only case that remained.

On Friday, Newark, N.J., federal district court judge Susan Wigenton granted a motion to dismiss class action securities fraud claims pending since June 2010 against Pfizer and five former Wyeth executives. In a 14-page decision (here), Judge Wigenton concluded that the named plaintiff failed to adequately plead that the defendants misled investors about the success of clinical trials for bapineuzumab, a potential blockbuster drug developed by Pfizer and Elan to slow or prevent the effects of Alzheimer’s.

Named plaintiff Security Police and Fire Professionals of America Retirement Fund is represented by liaison counsel at Carella, Byrne, Cecchi, Olstein, Brody, & Agnello and co-lead counsel Grant & Eisenhofer and Kessler Topaz Meltzer & Check. In their May 2011 amended complaint, the plaintiffs lawyers claimed that the defendants “knowingly concealed material information and made false and misleading statements relating to Wyeth’s most important pipeline drug, bapineuzumab,” causing investors to pay artificially high prices for company stock between May 2007 and July 2008.

Friday’s ruling is a clear victory for Pfizer counsel Stephen Matthews of New Jersey firm Porzio, Bromberg, & Newman, but it’s harder to sort out which of Pfizer’s out-of-town firms deserves credit for the win. Cadwalader, Wickersham & Taft was of counsel for the company until long-time Pfizer counsel Dennis Block left Cadwalader for Greenberg Traurig last September. Williams & Connolly replaced Cadwalader on the briefs following Block’s departure, but no W&C partner is named in any court filings. (According to Pfizer, Williams & Connolly’s John Villa and George Borden represent the company; Villa wasn’t immediately available to comment on the ruling.)

Porzio’s Matthews declined to comment. A Pfizer spokesman said Pfizer was “pleased” with Friday’s decision. “It has been our contention all along that this suit has no merit,” he said. We left a message with plaintiffs liaison counsel James Cecchi of Carella Byrne but didn’t hear back.

Last June Manhattan federal district court judge Alvin Hellerstein dismissed a three-year-old consolidated securities class action against Elan that closely mirrored the case against Pfizer. (Pfizer’s lawyers cited the New York dismissals heavily in their own motion to dismiss the Newark case.) The named plaintiffs in the Manhattan litigation are represented by Scott + Scott and Robbins Geller Rudman & Dowd; Brower & Piven and Labaton Sucharow represent additional investors appearing as movants.

The New York plaintiffs have appealed Judge Hellerstein’s ruling to the U.S. Court of Appeals for the Second Circuit. Elan is represented by Shearman & Sterling.