By Lisa Richwine

WASHINGTON (Reuters) - Deaths of 51 U.S. patients who took widely prescribed drugs to treat attention deficit disorder prompted regulators to start watching for heart attacks, high blood pressure and other problems in 2004, a report released on Wednesday said.

The Food and Drug Administration staff did not say the drugs were responsible for the fatalities, but they urged close monitoring for "the rare occurrence of pediatric sudden death during stimulant therapy."

The report was released one day ahead of an FDA advisory panel meeting on how best to study potential risks from the drugs, which include Shire Pharmaceuticals Group Plc's Adderall and Novartis AG's Ritalin.

FDA staff scientists and experts will provide updated information at the meeting about serious health problems that have been reported, the agency said.

Use of drugs to treat attention deficit hyperactivity disorder, or ADHD, was controversial before the cardiac issue emerged, with many doctors and parents arguing the medicines are overprescribed.

The FDA said it decided to seek input from an advisory panel after reports of sudden death, high blood pressure, heart attacks and strokes in children and adults who took the medicines.

Through 2003, 24 deaths were reported among patients who took Adderall for ADHD, the FDA staff report said.

Another 16 deaths were reported through 2003 in patients who took Ritalin or other attention deficit drugs known as methylphenidates, the report said. Eleven deaths were reported among other drugs besides Adderall in the amphetamine class, it said.

"Conclusions about the relative safety of these two stimulant therapies cannot be made on the basis of this analysis," the FDA staff said.

Shire spokesman Matthew Cabrey said data have not shown any correlation between Adderall and the sudden deaths reported among children. He said the company supports the FDA's review of the matter.

Health Canada temporarily suspended Adderall sales last year after 20 reports of sudden death in people who took it. The agency allowed Adderall back on the market after concluding it could not prove the drug was more risky than other therapies.

Shares of British firm Shire fell 3.2 percent to 890.2 pence in London trading.