In what appears to be one of the most important “gate-keeping” rulings ever rendered in a mass-tort case, the federal judge presiding over 3,000 personal injury lawsuits against Pfizer (PFE) has barred plaintiffs’ experts from testifying that Celebrex can cause increased risk of heart failure and stroke at what Pfizer says is the drug’s most commonly administered dosage, 200 milligrams per day. The ruling is here..

Judge Charles Breyer of San Francisco — U.S. Supreme Court Justice Stephen Breyer’s brother — rejected, however, Pfizer’s more audacious request for him to also bar such testimony relating to 400 mg/day dosages, which were commonly prescribed for rheumatoid arthritis. Pfizer conceded that 800 mg/day dosages would cause increased risk.

Celebrex is the only Cox-2 inhibitor class of painkiller still sold in the United States; Merck’s (MRK) Vioxx was pulled in September 2004 due to concerns with increased cardiovascular risk, while Pfizer’s Bextra was pulled in April 2005 due to a melange of safety reasons, including cardiovascular risk.

Two leading plaintiffs lawyers in the litigation told the Wall Street Journal last night, see here, that the ruling would affect only about one-third of the cases. (That sounds optimistically low. Merck, for instance, has claimed that, as of September 30, 2007, more than 5,500 “plaintiff groups” who sued over Vioxx had either had their suits dismissed or had voluntarily withdrawn them, and that 20 suits were withdrawn or dismissed after they were actually set for trial; in many of these cases the plaintiffs were having difficulty proving that they had ever taken Vioxx.)

Pfizer’s national liaison counsel in the case (and its national coordinating counsel for all Bextra/Celebrex litigation) is Amy Schulman of DLA Piper. She was not immediately available for comment.

Judge Breyer had held three-days of hearings in San Francisco in October, hearing testimony from four plaintiffs experts and one defense expert. Only two of the plaintiffs experts opined that 200 mg/day could cause increased cardiovascular risk, and Judge Breyer’s caustically found that their views lacked sufficient scientific basis to even allow a jury to consider them.

“Dr. [Neil] Doherty, a clinical physician with no relevant research experience and who developed his opinion for the purpose of testifying,” Breyer wrote, “bases his opinion on a study that he fundamentally misunderstood, is counter to the great weight of the evidence, and, by his own admission, does not make biological sense. . . . Dr. [Maryilyn] Rymer’s . . . opinion is also not good science. She ignores all the evidence that contradicts her litigation-created conclusion and instead bases her opinion on the same cherry-picked study as Dr. Doherty, even though that study suffers from the exact same limitations that caused her to reject other studies that do not support her conclusion. She also relies on an unpublished, non-peer reviewed study that does not disclose its design or confidence intervals.”

At the same time, Judge Breyer rejected Pfizer’s long-shot attempt to score a nearly total knock-out punch by excluding testimony that 400 milligrams/day increased risk. Pfizer’s claim in this regard had been contradicted on its face by the so-called APC study, “a large, long-term, randomized, placebo-controlled, double-blind, multi-center clinical trial that was halted after 33 months [in December 2004] because it demonstrated a statistically significant risk of heart attack, stroke, and heart failure at 400 mg/d.” (The increased risk had been 260%. At 800 milligrams a day, the increased risk was 340%.)

Although Judge Breyer’s ruling does not apply to cases filed in state court, New York State supreme court justice Shirley Werner Kornreich, who presides over hundreds of cases there, where Pfizer is headquartered, sat in with Judge Breyer at the October hearings in San Francisco. It’s not clear yet how she will rule.

For coverage in a pharmaceutical journalist’s blog, see here, and for coverage by a pharmaceutical industry defense lawyer’s blog, see here.