WASHINGTON – The Food and Drug Administration has sent a warning letter to Novartis Animal Health U.S. Inc. because of what federal officials say were late reports on the death of cats being tested with a new painkilling drug.

The drug being tested, Deramaxx, is in the same chemical family as Vioxx and Celebrex, two human drugs that have been linked to heart attacks.

The FDA’s Nov. 29 letter said that the death of 14 cats that were being tested with Deramaxx was reported to the FDA months past the deadline for such reports. Regulations require such reports to be filed within 15 days.

Novartis spokesman Joseph Burkett said the cats were participating in an experiment testing whether Deramaxx could be used in cats. He said the company is no longer conducting such tests.

The experiment concluded in July 2003, but the adverse events were not reported to the FDA until Feb. 24, just after an inspection of the Novartis animal drug facility in Greensboro, N.C., according to the FDA letter.

Deramaxx, which has the chemical name of deracoxib, is approved for use in tablet form by dogs. The drug’s purpose is to relieve arthritis and surgical pain in dogs.

The drug works by blocking what is known as the COX 2 enzyme. The effect is similar to that of Vioxx and Celebrex, human arthritis drugs that have been linked in studies to heart attacks and stroke.