Plaintiffs' Causation Expert Excluded in Viagra MDL

The federal judge overseeing the multidistrict litigation involving the erectile dysfunction drug Viagra has decided to exclude the testimony of the plaintiffs' key expert witness on causation. In re: Viagra Products Liability Litigation, case number 06-md-01724 (D. Minn. 8/19/09).

The litigation stems largely from an announcement in July, 2005 by the FDA that it was updating its labeling requirements for Viagra to reflect a small number of post-marketing reports of sudden vision loss, attributed to nonarteritic anterior ischemic optic neuropathy (NAION), an eye condition that can result in partial or total blindness.  An MDL consolidated hundreds of product liability lawsuits alleging a link between Viagra and NAION.
 

Judge Paul Magnuson of the U.S. District Court for the District of Minnesota had ruled last year that the general causation opinions of three of  the plaintiffs' experts should be excluded.  This motion related to plaintiffs' sole remaining general causation expert, Dr. Gerald McGwin.  This expert had authored a study, published in the British Journal of Opthalmology, which indicated that male Viagra users with a history of heart attacks had a statistically significant increased risk of suffering NAION. The court had originally denied Pfizer’s Daubert challenge to Dr. McGwin, largely because his study was peer-reviewed, published, contain[ed] known rates of error, and seemingly resulted from generally accepted epidemiological research.  In re Viagra Products Liab. Litig., 572 F. Supp. 2d 1071, 1081 (2008). In January, Judge Magnuson ruled that Pfizer could seek additional discovery related to McGwin's study, and in July, the judge denied the plaintiffs’ motion to have McGwin provide live testimony at a Daubert rehearing.
 

That additional discovery revealed that the study contained discrepancies that raised “serious concerns” about its reliability. In fact, the study contained numerous “acknowledged inaccuracies,” chief among them the inclusion of numerous patients in McGwin's data-set who had not taken Viagra until after they were diagnosed with NAION.  Dr. McGwin acknowledged that the statistics
in his study would have been different had those individuals (11 of 27 patients who
reported drug use) been coded as unexposed rather than as exposed. The discrepancies between the dates of first use on the original survey forms and in Dr. McGwin’s later electronic data set weaken the McGwin study’s assessment of temporality, thereby impair the study’s ability to contribute meaningfully to Dr. McGwin’s opinion about general causation.

Second, the statistical methods actually used to produce the numbers in the McGwin study as published were not the statistical methods that the study said were used. Even if a later reanalysis purportedly confirmed  the findings of the original study, the fact that the methodologies described in the study were not the actual methodologies used clearly also undermines the reliability of the McGwin study as published.

Third, the study was unreliable because it mischaracterizes one of its main findings—that men with a personal history of myocardial infarction and drug use have a significantly higher risk of NAION. The patients were actually asked whether they had a family history of myocardial infarction; no one was asked about personal history. These mis-codings regarding myocardial infarction added yet another layer of unreliability to the McGwin study as published.

The judge concluded that "Almost every indicia of reliability the Court relied on in its previous
Daubert Order regarding the McGwin Study has been shown now to be unreliable. Peer
review and publication mean little if a study is not based on accurate underlying data."

Lastly, Judge Magnuson denied the plaintiffs' motion for leave to file a supplement to McGwin's expert report, which included a reanalysis of the data, concluding that the report's untimely
submission was neither harmless nor justified. The reanalysis lacked even the basic indications of reliability — peer review and publication — that the original had seemingly had, and it had also been produced simply in response to concerns raised in the litigation.

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