WASHINGTON - Federal officials will have a new tool to use to find potential safety problems with medicines and medical devices already on the market.

Under rules announced yesterday by the Department of Health and Human Services, Food and Drug Administration investigators will have the authority to review prescription drug use by millions of participants in the Medicare drug program to look for safety issues.

The FDA has been under increasing pressure to develop a drug-surveillance system since the pain reliever Vioxx, made by Merck & Co. Inc., was pulled from the market in 2004 after it was linked to an increased risk of stroke and heart attack.

The regulations introduced by the Department of Health and Human Services will enable federal agencies, states and academic researchers to use Medicare claims data. Protections will be put into place to protect patient privacy and trade secrets.

Medicare beneficiaries use an average of 28 prescriptions a year, and those in poor health use an average of 45, giving officials a huge database of health records to tap into.

Officials said they would no longer have to wait years to see how a drug or medical device affects millions of people.

"The era of wait and see is going to become the era of tell me right now," said the FDA commissioner, Andrew von Eschenbach.

The FDA currently relies on physicians and patients to report suspected adverse events. Often, it takes a number of cases before someone at the agency detects a pattern that is worth investigating.

The agency then conducts an investigation to determine if the side effects were caused by the drug. At the first hint of trouble, the FDA will now be able to query databases involving tens of millions of patients. It will not only be able to see the medications used by patients, but whether they had lab work done or whether they had to be hospitalized.

The first batch of records the agency will have at its disposal will be from 25 million Medicare beneficiaries. Later, private companies will contribute medical data, said Health and Human Services Secretary Mike Leavitt.