here's a recent case that demonstrates that it matters.
In one its most significant decisions this Term, the United States Supreme Court has ruled in favor of musician Diana Levine in her lawsuit against the pharmaceutical company Wyeth. What the decision means is that drugmakers do not get a complete defense to state law products liability lawsuits simply by getting an OK from the U.S. Food and Drug Administration (FDA) for their drugs' warning labels.
The case was brought after the plaintiff, professional musician Diana Levine, went in to a local clinic for treatment of a migraine headache. After a first round of treatment failed to help, her doctor administered Wyeth's nausea drug Phenergan using a method called an "IV-push" which is basically a direct injection into a vein. That doesn't sound like too big a deal, but Phenergan is "corrosive and causes irreversible gangrene if it enters a patient’s artery," which is exactly what happened to Levine. She ended up getting gangrene from the injection, resulting in the amputation of her hand and forearm, substantial medical expenses, and the loss of her livelihood as a musician.
Levine sued in Vermont state court and won nearly $7 million, arguing that Wyeth should have placed better warnings on its labels regarding intravenous injection of the drug. Wyeth, on the other hand, indicated that its label had been "deemed sufficient by the when it approved Wyeth’s new drug application in 1955 and when it later approved changes in the drug’s labeling." Notably, the warning label actually did point out the dangers of inadvertently injecting the drug into an artery, including "gangrene requiring amputation". Those FDA approvals, Wyeth argued, should provide it with a complete defense to Levine's claims because the federal drug labeling law under the Federal Food, Drug, and Cosmetic Act preempts (i.e. trumps) state law product liability claims based on inadequate warnings.
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http://commonlaw.findlaw.com/2009/03/diana-levine-wins-supreme-court-case-and-deals-wyeth-drugmakers-serious-loss-product-liability-suit-.html