By Constanza Villalba, Globe Correspondent, 3/9/2004

Roughly once a day, a dog or cat lands in the emergency room at Angell Animal Medical Center in Boston because its owner benevolently -- if misguidedly -- gave it a pain-reliever like Advil or Tylenol, said Kiko Bracker, an emergency veterinarian there. These drugs, it turns out, are toxic to pets, as are a bevy of other human medications.

In dogs and cats, so-called nonsteroidal anti-inflammatory drugs, including Advil, Motrin and Aleve, can cause stomach ulcers, which sometimes bleed, as well as kidney damage. The same is true for people who use these drugs persistently, but in pets, the effects can occur after just one dose. And the usual size difference between people and their pets is just a small part of the problem.

Most human medications come in doses appropriate for a 100- to 200-pound patient, "but even if you gave your pet a proportionally smaller dose of an NSAID, you wouldn't protect it from the drug's potentially toxic effects," said veterinarian Amy Shroff, chief of staff in the Emergency and Critical Care Department at the Veterinary Emergency and Specialty Center of New England in Waltham. That's because dogs and cats don't metabolize these drugs as efficiently as humans do.

How a dog or a cat processes an NSAID, or any other drug, varies according to its size, age, overall health, and body fat composition. (Fat, in general, slows the flow of drugs into the bloodstream.) Some pets escape NSAID exposures unscathed, while others may lose their appetite, vomit, or develop diarrhea. Animals that get higher NSAID doses may also drink or pee excessively. If untreated, pets affected by NSAIDs can bleed out from their gut, and their kidneys may completely shut down.

Acetaminophen, the active ingredient in Tylenol, has even worse repercussions, especially for felines.

"A cat that's eaten a Tylenol will lay there swooning," said Elizabeth Ellis, another emergency veterinarian at the veterinary emergency center, "and their face and paws may swell."

In cats, she said, acetaminophen destroys the cells of the liver and renders red blood cells incapable of carrying oxygen. As a result, cats given the drug quickly begin to suffocate and can die from just one standard-dose Tylenol.

Steve Hansen, the director of the national Animal Poison Control Center, said his staff gets plenty of calls from people who've medicated their pets, "but the bigger problem by far," he said, "happens when animals get into medicine bottles that have been left in their reach."

The poison control center runs an around-the-clock national hot line at 1-888-426-4435 for pet owners and veterinarians dealing with all kinds of animal poisonings. Last year, the center managed more than 28,000 cases involving human pharmaceuticals, most commonly NSAIDs, antidepressants, and cold and flu preparations, he said.