Washington  - The US Supreme Court ruled Wednesday that patients can sue drugmakers for failing to warn adequately of serious side effects, even if their warning labels were approved by the federal government, according to a landmark case that could expose the industry to billions of dollars in damages.

In a 6-3 decision, the court upheld a 7-million-dollar reward to a professional musician whose arm had to be amputated after she was improperly injected with Phenergan, an anti-nausea drug produced by pharmaceutical firm Wyeth.

The ruling opens the door for thousands of pending lawsuits - worth billions of dollars - by patients against Wyeth and other pharmaceutical companies over inadequate warnings about their products.

Diana Levine had already settled a lawsuit against the hospital that injected her improperly, causing the loss of her arm and her livelihood as a musician. But she also alleged that while Wyeth warned of the dangerous risks in using Phenergan, it failed to instruct physicians on the safest method of administering the drug.

Wyeth had argued that its warnings were approved by the US Food and Drug Administration, the US federal regulator. But Justice John Paul Stevens, writing for the court, said it was up to the drugmakers to go above and beyond the FDA's own judgements.

"The FDA has limited resources to monitor the 11,000 drugs on the market, and manufacturers have superior access to information about their drugs, especially in the post-marketing phase as new risks emerge," Stevens wrote. (dpa)