WASHINGTON?The US Supreme Court ruled Wednesday that pharmaceutical companies can be sued over serious side effects of drugs even when warning labels have been approved by the Federal Drug Administration.

The 6-3 judgment against the drug maker Wyeth opens the door to litigation in thousands of similar cases, lawyers say.

The high court found in favor of Diana Levine, a musician who was awarded $6.7 million in damages by a Vermont court after she developed gangrene and lost her right forearm because of the anti-nausea drug Phenergan.

The court rejected arguments by Wyeth, the drug's manufacturer, that the Federal Drug Administration had approved warning labels for the drug and that that took precedence over the state law under which the suit was brought.

"In short, Wyeth has not persuaded us that failure-to-warn claims like Levine's obstruct the federal regulation of drug labeling," Justice John Paul Stevens writing for the majority said.

"Congress has repeatedly declined to preempt state law, and the FDA's recently adopted position that state tort suits interfere with its statutory mandate is entitled to no weight," the opinion said.

Lawyers said the judgment opens the way for individuals to bring lawsuits against manufacturers for negligence even when the FDA has approved a drug and the warning labels it bears.

Wyeth said the ruling was "disappointing," not only for the company but for patients and public health generally.

"Patients are best served by a national standard for the labeling of prescription medications -- set by the medical and scientific experts at the U.S. Food and Drug Administration (FDA)," it said in a statement.

"When lay juries are permitted to second-guess the experts at FDA on the benefits and risks of particular medicines, the result is uncertainty for patients and doctors alike about how and when to use prescription drugs," it said.

The extent of Wyeth's potential long-term liability is unclear.

At least 20 other cases in which the use of Phenergan resulted in gangrene and amputation have been reported, according to evidence presented to the court by Levine.

A Vermont jury awarded Levine $7.4 million in damages, but the amount was reduced by the court.

Levine's ordeal began on April 7, 2000 when she went to her local clinic for treatment of a migraine headache.

She received an intramuscular injection of Demerol and Phenergan for nausea, but because the combination did not provide relief she returned later in the day and received a second set of injections of both drugs.

This time, a physician's assistant administered the drugs intravenously. The Phenergan entered Levine's artery, either because the needle penetrated an artery directly or because the drug escaped from the vein into surrounding tissue and came into contact with arterial blood.

"As a result, Levine developed gangrene, and doctors amputated first her right hand and then her entire forearm," the court said.

"Levine incurred substantial medical expenses and the loss of her livelihood as a professional musician," it said.

The trial court concluded that Levine's injury would not have occurred if Phenergan's label had included an adequate warning about the risks of delivering it by means of intravenous injection.

"In finding Wyeth negligent as well as strictly liable, the jury also determined that Levine's injury was forseeable," the Supreme Court said.

But Justice Samuel Alito, writing for the minority, called the ruling a "frontal assault" on the FDA's regulatory regime for drug labeling.

"Whether wisely or not, the FDA has concluded over the course of extensive, 54-year-long regulatory proceedings that the drug is 'safe' and 'effective' when used in accordance with its FDA-mandated labeling," he wrote.

Alito argued that the FDA had reviewed the risks the drug posed, and was aware of cases of gangrene associated with the "push" IV delivery used on Levine.

He said the labels highlighted those risks, and warned specifically that inadvertent injection into the artery could result in gangrene.

"The unfortunate fact that respondent's healthcare providers ignored Phenergan's labeling may make this an ideal medical malpractice case," he wrote.

"This case illustrates that tragic facts make bad law," he wrote.