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In re Zoloft (Sertraline Hydrocloride) Products Liability Litigation

United States District Court, E.D. Pennsylvania

August 12, 2014



CYNTHIA M. RUFE, District Judge.

Zoloft (sertraline hydrocloride) is a prescription antidepressant, commonly used to treat depression, anxiety, and other mental health conditions.[1] Plaintiffs in this multi-district litigation allege that Zoloft, when taken during pregnancy, causes birth defects in the children born to exposed mothers. The Plaintiffs' Steering Committee ("PSC") proposes to offer the testimony of various expert witnesses on the issue of general causation. These include Dr. Sadler, Dr. Cabrera, and Dr. Levin. Before the Court is Defendants' Motion to exclude the testimony of these three experts. Pfizer does not challenge the qualifications of the experts. The Court has reviewed the expert reports, as well as Defendants' rebuttal expert reports and the briefs of the parties, and held a Daubert hearing at which testimony and evidence were presented in support of each position.


Federal Rule of Evidence 702 reads:

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if:
(a) the expert's scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;
(b) the testimony is based on sufficient facts or data;
(c) the testimony is the product of reliable principles and methods; and
(d) the expert has reliably applied the principles and methods to the facts of the case.

The Third Circuit has distilled this rule to two essential inquiries: 1) is the proffered expert qualified to express an expert opinion; and 2) is the expert opinion reliable?[2] Here, the challenge is to the reliability of the experts' opinion, not their expertise in their respective fields.

Under the Third Circuit's framework, the focus of the Court's inquiry must be on the experts' methods, not their conclusions. Therefore, the fact that Plaintiffs' experts and Defendants' experts reach different conclusions does not factor into the Court's assessment of the reliability of their methods. The experts must use good grounds to reach their conclusions, but not necessarily the best grounds or unflawed methods.[3]

Expert evidence must be relevant and reliable to be admissible. The Court must consider: 1) whether the expert's theory can be tested; 2) whether studies have been subject to peer review and publication; 3) the potential for error in a technique used; and 4) the degree to which a technique or theory (but not necessarily a conclusion) is generally accepted in the scientific community.[4] The burden is on Plaintiffs to demonstrate that their experts used reliable scientific methods to reach their opinions.


Drs. Sadler, Cabrera, and Levin have been retained by the PSC to opine as to whether: (1) there is a plausible biological mechanism by which Zoloft could cause the injuries at issue in this litigation; and (2) Zoloft causes the birth defects at issue when taken by pregnant women, in clinically appropriate doses, during the first trimester of pregnancy.

A. Opinions Regarding Plausible Biological Mechanisms

Biological plausibility is one of the criteria scientists need to address in opining as to whether an association between a substance and an adverse outcome reflects a causal relationship (i.e. whether the substance is a teratogen), and the PSC has asked three experts to address this criteria.[5] All three experts opine that there is at least one plausible biological mechanism by which SSRIs generally, and Zoloft particularly, may alter embryonic development. In their expert reports, they set forth the basis for their opinions regarding the plausible biological mechanism of injury.

1. Dr. Cabrera

Dr. Cabrera is a teratologist, with a Ph.D. in Medical Sciences, whose research focuses on identifying agents that may cause or prevent birth defects. He has conducted in vitro and in vivo animal studies, most often using mouse models. His research focuses on the impact of immunizations and anti-epileptic medications on developing embryos. He has never performed studies of Zoloft or other SSRIs, but has reviewed relevant publications in connection with this litigation.[6]

Dr. Cabrera opines that serotonin is an important signaling molecule for organ development in a developing embryo, regulating "cell proliferation, migration, differentiation, and gene expression... processes [ ] fundamental to creating a normally formed embryo."[7] He further opines that SSRI exposure "alters normal serotonin signaling pathways, "[8] and that "[t]here exists a biologically plausible mechanism of teratogenic action (MOA)... [A]lteration of serotonin signaling by SSRIs, including sertraline, can impact embryonic development resulting in several different congenital malformations, involving various body and organ systems...."[9] Thus SSRIs, including Zoloft, are "capable of causing birth defects."[10]

In forming his opinion for this litigation, Dr. Cabrera reviewed some of the relevant scientific literature on Zoloft, with a particular focus upon Pfizer's pre-clinical animal reproductive toxicity studies data on rodents and rabbits, the only whole animal studies of which he is aware.[11] Pfizer's studies were conducted in the 1980s and presented to the FDA in the application for approval of Zoloft. In his report and testimony, Dr. Cabrera discussed and critiqued Pfizer's studies. For example, he testified that although Pfizer noted an increase in pup deaths in Zoloft-exposed rats (especially at the high doses), when Pfizer looked at the timing of exposure, it concluded that the vulnerability for pup death was late in gestation (days 16 to 21), not during organogenesis.[12] When Dr. Cabrera reanalyzed the data, combining all groups exposed prior to day 15 of gestation, he found a nearly statistically significant increase in pup death in that combined group as well.[13] He concluded that the studies suggest a teratogenic effect, but were underpowered to test this effect, [14] particularly with regard to birth defects, and opines that it is "questionable whether any reasoned interpretation could be derived from these studies."[15]

Dr. Cabrera also reviewed in vitro studies testing the importance of serotonin pathways in embryonic development and the impact of disruptions to those pathways on various organs and systems. He concluded that there is a plausible mechanism of action by which Zoloft may impact embryonic development and produce the birth defects at issue in this litigation.

Pfizer argues that Dr. Cabrera has never tested his hypothesis about Zoloft, noting that although "in his non-litigation work he conducts and publishes peer-reviewed animal studies regarding medications and birth defects... Dr. Cabrera has performed no studies of Zoloft, or any other SSRI, to test any aspect of his hypothesis." While hypothesis testing is indisputably a requirement for scientifically reliable opinions, the Court does not agree that Dr. Cabrera must perform his own studies in order to form a reliable opinion. It is acceptable to rely on the hypothesis testing of others, so long as one addresses both supportive and contrary evidence in reaching one's opinion. In his analysis of the Pfizer animal studies, Dr. Cabrera demonstrates that he has done just that: he did not ignore the findings of those studies from ...

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