The introduction of a generic alternative can kill a blockbuster drug's sales faster than Nicole Richie can get out of jail. But losing a patent might not just hurt sales of the covered drug; it also affects competitors because patients will switch from a brand name to a competitor's generic.

Pfizer (NYSE:PFE) is trying to fight the slide in sales of its patented Lipitor, as some patients switch to generic versions of Merck's (NYSE:MRK) Zocor, made by Teva Pharmaceuticals (NASDAQ:TEVA) and other firms. The company didn't run a major double-blind clinical trial to compare the two -- that would be way too expensive. Instead, Pfizer did an observational study of a database of 11,520 patients, some of whom had switched to generic Zocor and some who had remained on Lipitor.

The study found a 30% increase in the relative risk of major cardiovascular events in patients who switched to generic Zocor, compared to those remaining on Lipitor. The results aren't that surprising; Lipitor is more effective at reducing cholesterol levels than Zocor.

In a separate analysis of the cohort of patients, Pfizer found that patients who switched from Lipitor to generic Zocor were more than twice as likely to discontinue their treatment, compared to those who remained on Lipitor therapy. While I don't doubt the data's accuracy, it seems like Pfizer is grasping at straws here. There's no hard evidence that the switch in drugs spurred patients to discontinue treatment.

The first switch may have been because Lipitor wasn't working, and neither did the generic Zocor. Perhaps the switch to the generic drug was financially driven, and the patients who switched were more likely discontinue any treatment for monetary reasons. Those are two of many possible explanations.

It's also possible that the study could help Merck. It markets two cholesterol-fighting drugs -- Vytorin and Zetia -- with Schering-Plough (NYSE:SGP). The study might convince a few managed-care organizations, like Aetna (NYSE:AET) and UnitedHealth Group (NYSE:UNH), that switching to the less-effective Zocor from any other cholesterol-fighting drug might be a bad idea. After all, heart surgeries are far more expensive than the difference in price between generic and brand-name drugs.

More Foolishness to get the blood flowing:

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool's disclosure policy has a good heart.