Pfizer Savors a Rare Victory in War Over Whether Viagra Causes Blindness

Last Updated Apr 23, 2010 5:33 PM EDT

Pfizer (PFE) has suffered through a rash of lousy legal news recently but there's one area -- Viagra litigation -- where everything is going the company's way. It's even forcing a rethink on the quality of published research that suggests Viagra can damage your eyesight.

A recent ruling by a Minnesota federal judge is a rare case of product liability litigation actually helping a company. In this case, Pfizer discovered that a study of Viagra that showed the drug triggered eye abnormalities in its users was riddled with errors.

As early as 1999 and 2003, there were reports that some Viagra users had difficulty perceiving subtle changes in color or even lost their eyesight. Three percent of Viagra users experience "abnormal vision," according to the drug's FDA-approved prescribing information.

The theory is that Viagra lowers the blood supply -- and the oxygen within it -- to the optic nerve. That's triggered a bunch of lawsuits which were gathered together into a "multidistrict litigation" pool in federal court.

The plaintiffs in the case wanted to use Dr. Gerald McGwin as an expert witness. He was the author of a study titled Non-Arteric Ischaemic Optic Neuropathy and the Treatment of Erectile Dysfunction in the British Journal of Ophthalmology in February 2006, which found that men with a history of myocardial infarction and Viagra use had a statistically significant increased risk of suffering from eye damage. Hypertension also created a non-significant increased risk, McGwin found.

Normally, when plaintiffs sue drug companies, the discovery process turns up a bunch of embarrassing internal documents and emails. This time, the embarrassment occurred on the plaintiffs' side. Pfizer found discrepancies between the original research forms used by McGwin and his published results, and that he used an inappropriate statistical test. (There were only 76 patients in the study to begin with.)

For those reasons, Pfizer successfully persuaded the judge to remove McGwin, the plaintiffs' only remaining expert witness, from the case. The judge wrote:

... the miscodings and errors described above effectively undermine the reliability of the McGwin Study as published...
Then Pfizer pressed further: it wanted McGwin's confidential discovery documents turned over by the University of Alabama Birmingham to the journal, so that the journal could consider retracting the study. Pfizer actually lost that ruling because UAB doesn't want to turn the documents over via Pfizer. But the judge noted that the university was going to comply with any request the journal made for the source material.

Why would Pfizer go so far, having already decimated the plaintiffs' expert? The notion that Viagra damages your eyesight or makes you see blue is ingrained into the culture in just the same way sleep-eating is for Sanofi-Aventis's (SNY) Ambien. Even an episode of the HBO show Big Love revolved around the trope.

Problem is, it may not be true. Here's a study (funded by Pfizer) of 13,400 men that shows no link. Eye damage may just be caused by the underlying circulatory problems that cause erectile dysfunction, and not the blue pill that treats it.

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Image by Flickr user The Gifted Photographer, CC.