BALTIMORE (AP) _ After hearing from worried customers, a supermarket chain and one of the nation's largest pharmacies have decided to stop sharing patient medical information with a marketing firm.

Giant Food Inc. of Landover, Md., placed full-page advertisements in The (Baltimore) Sun and The Washington Post on Wednesday announcing its decision after critics said the practice was unethical and raised privacy concerns.

CVS Corp. of Woonsocket, R.I., also said it is ending the practice.

The companies provided patient data to Elensys Inc., a Woburn, Mass., company that specializes in computer database marketing. Elensys got paid to send customers prescription reminders and promotional literature for new drugs.

The Post on Sunday reported on the relationship between the three companies, adding that Elensys was sometimes paid by drug companies to send letters promoting new drugs.

Elensys receives prescription information from 15,000 pharmacies about millions of people each week and uses some of the most sophisticated computer equipment available to keep track of the records, the Post said.

After the story, a number of customers expressed fear that their medical information could become common knowledge among people who didn't have the need or right to know.

``Because of privacy concerns, we discontinued the program immediately,'' said Barry Scher, spokesman for Giant Food.

``We believe the program could greatly benefit certain patients,'' CVS spokesman Fred McGrail said, ``but based on some concerns expressed by some customers, we have decided to suspend the program.''

The companies said customers' medical confidentiality was never compromised.

People expect the information they give doctors and pharmacists to remain confidential, and a violation of that trust is a serious breach of medical ethics, said Dr. George Lundberg, editor of the Journal of the American Medical Association.

``When things are done to patients in the Western world, it is expected that they will be informed what is being done to them. In this instance, as far as I know, the patient hasn't been told,'' he said. ``I would expect patients across the country to resist this kind of process.''

Drugstore chains usually hire marketing companies to provide customer service, including reminders to fill prescriptions, said Susan Winckler of the American Pharmaceutical Association, which represents 50,000 pharmacists.

The APA, however, frowns on marketers using customer databases to mail solicitations for new products, she said.

Giant Food's ads said the company began sharing information in December after ensuring there were ``extensive safeguards'' in the Elensys contract to protect customer privacy.

Elensys was under contract to write customers letters on Giant Food stationery reminding them to fill prescriptions or giving other medical tips and suggestions, Scher said. The Post said some mailings were blatant advertisements for new drugs.

Giant operates about 170 food and drug stores in Maryland, Delaware, New Jersey, Pennsylvania and the District of Columbia. In Pennsylvania, its stores are called Super G, and are not associated with the Giant stores operated by Giant Food Stores Inc. of Carlisle, Pa.

CVS has 3,888 stores in 24 states and the District of Columbia.