Federal regulators have told the makers of the popular drugs Levitra and Zyrtec to pull some advertisements the regulators said made unsubstantiated claims.

The Food and Drug Administration said Friday it sent letters this week notifying Bayer Pharmaceuticals Corp. and Pfizer Inc. that a television commercial for Levitra and three direct-mail advertisements for Zyrtec made unsubstantiated claims of superiority over competing products.

In Levitra’s case, Bayer also failed to disclose FDA warnings and product information, the letter said. It was the fourth such warning for Pfizer about Zyrtec.

The commercial for Levitra, an erectile dysfunction drug, features a woman praising the drug, and, according to the FDA, implying that her sexual experience with her partner was satisfying as a result of her partner’s use of Levitra. She says the drug is “the best way to experience the difference.” The FDA said this is an unprovable claim.

The commercial also fails to highlight side effects and FDA warnings, the agency said.

Matthew Scampoli, a spokesman for Schering Corp., which markets Levitra for Bayer, said the 15-second commercial is one in a three-commercial campaign. He said the remaining commercials would remain on the air but said, “We are going to comply with the FDA’s request,” to pull the 15-second spot.

“We’re currently reviewing all our Levitra promotional material to address the issues raised by the agency,” he added.

The ads for Zyrtec compare two people; one obviously sick, sneezing or wiping her nose, and another who looks perfectly healthy. The captions of the ads imply that the healthy and alert-looking person has taken Zyrtec; the sickly and unhappy one has taken a different medication.

The FDA said it “is not aware of substantial evidence or substantial clinical experience demonstrating that Zyrtec is clinically superior” to any other available over-the-counter or prescription allergy medicine.

An attempt to reach Pfizer by telephone after business hours on Friday was unsuccessful.

The FDA requested that both companies cease the ad campaigns and respond in writing to the request. It also said that since this was the fourth warning about the same problem for Pfizer, that Pfizer include in its response an outline of how it plans to make “truthful, non-misleading and complete” corrections to its ads.