## Facts

- Hundreds of suits were centralized in an MDL alleging that Onglyza and Kombiglyze, FDA-approved type 2 diabetes drugs containing saxagliptin (a DPP-4 inhibitor), caused users to develop heart failure and that manufacturers failed to warn of that risk.
- A large randomized controlled trial (SAVOR) compared saxagliptin to placebo in 16,492 patients and reported a higher rate of hospitalization for heart failure in the saxagliptin group.
- To prove general causation (that saxagliptin can cause heart failure in humans), plaintiffs designated a single expert, cardiologist Dr. Parag Goyal.
- Dr. Goyal applied the Bradford Hill criteria, relying heavily on SAVOR and also citing animal studies.
- In his analysis, Dr. Goyal did not meaningfully address four other human studies that did not find a statistically significant association between saxagliptin and heart failure; he later acknowledged those studies were reasonably designed and did not show such an association.
- The district court excluded Dr. Goyal’s general-causation opinion under Federal Rule of Evidence 702 after finding methodological unreliability, then granted defendants summary judgment because plaintiffs lacked admissible general-causation evidence.
- After exclusion, plaintiffs sought 90 additional days to locate a replacement general-causation expert; the district court denied the request.

## Issues

1. Whether the district court abused its discretion under Fed. R. Evid. 702 and Daubert by excluding plaintiffs’ general-causation expert as methodologically unreliable.
2. Whether, after excluding the expert, the district court properly granted summary judgment because plaintiffs lacked admissible evidence of general causation.
3. Whether the district court abused its discretion by denying plaintiffs an additional 90 days to find a substitute general-causation expert.

## Decision

- The Sixth Circuit affirmed the exclusion of Dr. Goyal’s general-causation testimony.
- The Sixth Circuit affirmed summary judgment for defendants because plaintiffs lacked admissible expert evidence of general causation.
- The Sixth Circuit affirmed denial of plaintiffs’ request for a 90-day extension to secure a new general-causation expert.

## Legal Principles

- Trial courts have a gatekeeping duty under Fed. R. Evid. 702 to admit expert testimony only when it is based on reliable principles and methods reliably applied to the facts.
- An expert’s selective reliance on supportive data while failing to account for significant contrary evidence may render the methodology unreliable and justify exclusion.
- Where medical and statistical causation questions are outside lay understanding, plaintiffs generally must present admissible expert testimony; studies and regulatory materials typically cannot, standing alone, establish general causation for a jury.
- Summary judgment is appropriate when a plaintiff lacks admissible evidence on an essential element, including general causation in complex pharmaceutical injury litigation.
- In MDL management, district courts have broad discretion over scheduling and may deny late requests to reopen expert development absent good cause and diligence.

## Conclusion

The Sixth Circuit held that excluding plaintiffs’ sole general-causation expert was within the district court’s discretion because his methodology was unreliable, and that without admissible expert causation evidence plaintiffs could not proceed to trial; it also upheld the denial of additional time to find a replacement expert in a long-running MDL.


In re Onglyza (Saxagliptin) & Kombiglyze (Saxagliptin & Metformin) Prods. Liab. Litig., 93 F.4th 339 (6th Cir. 2024)