The U.S. Food and Drug Administration sent warning letters to several companies requesting that they stop distributing misleading promotional materials for their drugs.

The letters were sent in recent weeks to Eisai Co. (4523.TO), Auxilium Pharmaceuticals Inc. (AUXL), Cumberland Pharmaceuticals Inc. (CPIX) and Dainippon Sumitomo Pharma Co.'s (4506.TO) Sepracor unit, and posted on the FDA's website this week.

The FDA said a 60-second television advertisement for Sepracor's Lunesta sleep aid makes "unsubstantiated superiority claims" in violation of federal law. A voice-over in the ad says viewers who have trouble sleeping even after taking a sleep aid should ask their doctors about switching to Lunesta because Lunesta is "different." The ad says Lunesta "keys into receptors that support sleep."

The FDA said this language misleadingly implies that Lunesta is clinically superior to other insomnia medications, and that Lunesta might work where others fail. The agency says it's not aware of any evidence to support these claims. Also, the agency said the claim about how Lunesta works is misleading because there's still some uncertainty about the drug's mechanism of action.

The FDA requested that Sepracor stop distributing promotional materials such as the ad cited.

In a separate letter to Eisai, the FDA said a promotional video for brain-tumor treatment Gliadel Wafer minimizes the risk of the drug and overstates its efficacy in violation of federal law. The drug's risks, which include seizures, are relegated to the end of the video after several cues suggesting the video is over, when it's unlikely to draw the viewer's attention, the FDA said.

The FDA said a Cumberland Pharmaceuticals sales aid for Acetadote, which is approved to prevent liver injury after an overdose of the pain drug acetaminophen, contains unsubstantiated superiority claims and minimizes risk information.

The agency's letter to Auxilium said a direct-to-consumer patient brochure for the drug Xiaflex, a treatment for a hand deformity, overstates the drug's efficacy and minimizes its risks.

Representatives of the companies weren't immediately available for comment.

-Peter Loftus, Dow Jones Newswires; +1-215-656-8289; peter.loftus@dowjones.com