"We're very interested in being able to test these samples ourselves to determine the levels of those contaminants," said FDA spokesman Doug Arbesfeld. "What's significant is these things are there. They don't belong there."

The pain medication is the fifth contaminant found in pet foods during the past 2 1/2 months and can be toxic or lethal to pets, especially cats. It is not known if any animals became sick with acetaminophen poisoning, or died from it.

"We were looking for cyanuric acid and melamine, and the acetaminophen just popped up," Donna Coneley, lab operations manager for ExperTox Inc. in Deer Park, Texas, told the Pittsburgh Tribune-Review yesterday. "It definitely was a surprise to find that in several samples." At least five dog and cat food samples submitted by worried pet owners and pet food manufacturers contained varying levels of the pain reliever, she said. Only the food, not individual ingredients, were tested.

The medication was found most often with cyanuric acid, a chemical used in pool chlorination, Coneley said. Varying levels of melamine, a chemical used to make plastics, also were found among the hundreds of samples ExperTox tested, she said.

The contaminants were found in foods that are not among the more than 150 brands recalled since March 16, Coneley said. The highest level of acetaminophen was found in a dog food sample submitted by a manufacturer, she said. Coneley declined to identify the company but said its officials were given the results "well over a month ago."

That company should have -- but did not -- notify the FDA, which first learned of the acetaminophen findings after pet owners posted lab reports on the Internet, Arbesfeld said.

"With any poison, it's the amount that matters." said Dr. Wilson Rumbeiha, a Michigan State University pathologist who is working with the FDA on the pet food contamination investigation. His lab has screened for acetaminophen but found none, he said.

The highest level of acetaminophen found by the Texas lab -- 2 milligrams per gram of dog food -- is a large amount, Rumbeiha said. That is eight times what a 10-pound cat could safely consume, he said.

However, a 20-pound dog would have to eat more than 6.5 pounds of food in 24 hours to be poisoned, unless it ate the same contaminated food daily, Rumbeiha said.

A still-unmeasured amount of acetaminophen and cyanuric acid were found in cat food submitted by Don Earl, 52, of Port Townsend, Wash., whose 6-year-old cat, Chuckles, died in January.

He said he was suspicious of two flavors of Chuckles' Pet Pride food because his other two cats refused to eat it and because Chuckles, strictly an indoor girl, had been healthy.

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