MDL Court Strikes Plaintiffs’ Experts’ Testimony on Human Causation in Zoloft® Products Liability Litigation. This summer, the U.S. District Court presiding over a multi-district products liability litigation issued a pair of Daubert rulings striking all of plaintiffs’ experts’ testimony on human causation. The plaintiffs allege that Zoloft® (sertraline), a prescription medication sold by Pfizer, when taken during pregnancy, caused a wide variety of birth defects in the children born to the exposed mothers. Zoloft is commonly used to treat depression, anxiety, and other mental health conditions. Defendant Pfizer is represented by Quinn Emanuel.
The rulings are significant not only to the Zoloft MDL and other birth defects litigations nationwide, but they emphasize the strategic importance of identifying early in a litigation the procedural mechanisms necessary for the orderly resolution of key disputed issues, and demonstrating to the judge how those procedures will streamline litigation so that the court institutes them.
The mechanism identified in the Zoloft MDL was a two-phased Daubert proceeding in which general causation issues—applying across the board to the entire MDL docket—would proceed first, from discovery through Daubert rulings, and then be followed by specific-causation expert discovery in trial pick cases and Daubert motions, if necessary.
Following this sequence, including the exchange of expert reports on general causation, expert depositions, and briefing on Pfizer’s Daubert motions (plaintiffs did not file any Daubert motions of their own), the court convened a seven-day hearing in April 2014 to hear first-hand from the four well-credentialed experts that Pfizer had challenged in their Daubert motions.
Plaintiffs’ chief expert on general human causation was Anick Bérard, Ph.D., a perinatal pharmacoepidemiologist from the University of Montreal. She opined that the epidemiological literature supported that Zoloft, a selective-serotonin reuptake inhibitor (“SSRI”), is capable of causing a wide variety of birth defects impacting nearly every organ system in the human body. Plaintiffs also presented three other well-credentialed experts to testify regarding a supposed biological mechanism by which Zoloft could cause the myriad injuries at issue in the litigations.
In a Daubert ruling issued June 27, 2014, the district court held that Dr. Bérard’s conclusions were only possible because she deviated from established epidemiological methods. The court also held Dr. Bérard failed to acknowledge and distinguish, or otherwise address, research findings contrary to her litigation opinion, including her own peer-reviewed, published research: “Dr. Bérard takes a position in this litigation which is contrary to the opinion she has expressed to her peers in the past, relies upon research which her peers do not recognize as supportive of her litigation opinion, and uses principles and methods which are not recognized by the relevant scientific community and are not subject to scientific verification.” And, to find her “associations,” Dr. Bérard improperly “cherry-picked” the studies, and findings within the studies, that she said supported her opinions, while ignoring other data that do not show that Zoloft causes such defects. In re Zoloft (Sertraline Hydrochloride) Products Liab. Litig., __ F. Supp. 2d __, 2014 WL 2921648, MDL No. 2342 (E.D. Pa. June 27, 2014).
In a second Daubert ruling, issued August 12, 2014, the court addressed the three experts plaintiffs proffered on biological mechanism. The court noted that while these experts cited animal studies supporting their opinions, they did not address the absence of similar findings in humans or consider possible alternative explanations: “The court cannot allow unscientific speculation to be offered, even by genuinely talented scientists,” the opinion said. “The court holds that the evidence upon which the experts rely in their reports is not sufficient to support a non-speculative opinion that Zoloft can cause birth defects in humans when used at conventionally prescribed doses.”
The court further noted that the three ‘mechanism’ experts had never published their litigation opinion in peer-reviewed journals and that their theories were not generally accepted in their fields. The court also noted that the experts had failed to explain why the epidemiological data involving pregnant women who took Zoloft failed to show a link between Zoloft and defects in humans. In striking all testimony on human causation, the court held: “Here, the experts have given scant attention to the epidemiology research in their reports, and have failed to reconcile inconsistent epidemiological evidence with their opinions on human causation.” In re Zoloft (Sertraline Hydrochloride) Products Liability Litig., __ F. Supp. 2d __, MDL No. 2342, 2014 WL 3943916 (E.D. Pa. Aug. 12, 2014).
While striking all of plaintiffs’ experts’ testimony on human causation, the court held that certain opinions of the three mechanisms experts about biological plausibility based on the experimental animal studies otherwise met the Daubert test and were “generally reliable,” and would not exclude them “if they are otherwise admissible...” (emphasis added). In fact, the court’s June 2014 opinion noted that biological plausibility is irrelevant absent predicate epidemiological evidence, which plaintiffs lack: “the Court notes that the biological mechanism research does not, at this time, establish: 1) that each of the three developmental pathways hypothesized to be impacted by serotonin exist in humans; 2) the ideal range of serotonin in the developing organism (of any species); or 3) the range of serotonin present in the developing embryo when a pregnant woman is exposed (or unexposed) to Zoloft in pregnancy. In addition to the many unanswered questions about the proposed mechanism, in vitro and in vivo animal studies are ‘unreliable predictors of causation in humans,’ in the absence of consistent data from human epidemiologic studies.” In re Zoloft , __ F. Supp. 2d. at ___, 2014 WL 2921648, at *11.
Following the Zoloft rulings, the plaintiffs have sought to name a new expert on general causation, Pfizer objected, and the parties are continuing to brief this issue. It remains to be seen whether the district court will reject plaintiffs’ “Daubert ‘do-over’” request and allow Pfizer to seek summary judgment dismissing plaintiffs’ cases for lack of general causation—an essential element of each of their claims. In any event, the careful analyses undertaken by the court in its two Zoloft rulings will certainly be useful for other Daubert challenges on general causation opinions.