In today’s case, Chapman v. AstraZeneca, a Delaware state court granted summary judgment to the defendant pharmaceutical manufacturer after excluding the plaintiff’s causation expert under Delaware Rule of Evidence 702 because the expert’s opinion was not “stated in terms of medical probability.”

The plaintiff claimed that the defendant’s proton pump inhibitor, a class of drugs used to treat acid reflux disorders, caused her to suffer chronic liver disease. To prevail, the plaintiff had to present “evidence of both general and specific causation.” Chapman v. AstraZeneca Pharms. LP, 2022 WL 4740721, at *1 (Del. Super. Ct. 2022).

To establish specific causation, i.e., to prove that the defendant’s drug not only can cause chronic liver disease in principle but caused her chronic liver disease in particular, the plaintiff offered a medical expert. The expert opined that the plaintiff’s use of the defendant’s drug “could have contributed” and “may have contributed” to her chronic kidney disease.” 2022 WL 4740721, at *4. Arguing that the expert’s opinion was “speculative,” the defendant moved to exclude it under Delaware Rule of Evidence 702, which is worded similarly to the identically numbered, soon-to-be-amended federal rule.

Under Delaware’s interpretation of the U.S. Supreme Court’s Daubert decision, an expert medical opinion is not admissible unless the court “determine[s]” that it is “stated in terms of reasonable medical probability or a reasonable medical certainty.” 2022 WL 4740721, at *2 (quoting O’Riley v. Rogers, 69 A.3d 1007, 1011 (Del. 2013)).

The Chapman court found that the plaintiff’s expert opinion did not satisfy this standard.

The court made clear that “[e]xpert witnesses do not have to explicitly use the words ‘reasonable medical certainty,’ but the overall summation of the opinion must lend itself to that conclusion.” 2022 WL 4740721, at *4. Thus, although “Delaware law provides for flexibility on the actual wording of expert testimony,” the expert’s “opinion must allow the Court to conclude that the expert finds: (i) one option more probable or likely than the others; (ii) that, having weighed varying factors or consulting material from his field, the expert has eliminated other possible causes; or (iii) that the varying factors have led the expert to suspect that this one factor is more likely the cause of the issue than another.” Id.

In Chapman, the expert’s opinion—the plaintiff’s use of a proton pump inhibitor “could have contributed to her developing … chronic kidney disease”—was “too speculative to be admissible” under that standard. 2022 WL 4740721, at *5 (emphasis added). Although the opinion “rule[d] out some possible causes” of the plaintiff’s disease, it “equivocate[d] as to … other [possible] causes.” Id. Indeed, the expert “admit[ted] that he finds it “impossible to discern if one particular agent was more likely than another to have caused” plaintiff’s disease. Id. In short, the court held that the expert’s causation opinion was inadmissible because it was “stated in terms of possibility and not probability.”

Having excluded plaintiff’s expert, the court granted the defendant summary judgment because the plaintiff could not carry her burden absent admissible evidence of specific causation.

A nice little win to start the week.