Over-the-counter aspirin for dogs is unnecessary and may cause more trouble than it is worth, according to some experts in veterinary analgesia.

In a recent online discussion, members of the Veterinary Information Network (VIN) expressed surprise to learn that aspirin comes in packages labeled for dogs and available on store shelves.

Aspirin has long been packaged and marketed for dogs. While the use of aspirin to treat animals has waned in the face of non-steroidal anti-inflammatory drugs (NSAIDs) and and other medications, owners and veterinarians have administered aspirin to alleviate pain in animals for at least a century.

That doesn't make it a good drug for dogs, said Steven C. Budsberg, DVM, a professor of surgery at the University of Georgia College of Veterinary Medicine.

“It's therapeutic efficacy in animals has never been proven, and efficacy has been shown for other drugs. I think we have a lot better products,” said Budsberg, who has written extensively on NSAIDs and osteoarthritis. He stated that aspirin is known to be particularly hard on the gastrointestinal tracts of canines.  

“It just rips the hell out of some of these dogs’ GI tracts,” he added.

Dr. Nicole Abramo, who practices in Buffalo, N.Y., said she was appalled to learn that some of her clients were buying dog aspirin at a local grocery store, and she was relieved to find out that the store planned to discontinue it.

Abramo said one of those clients had a dog that was limping. During an appointment, the client mentioned giving the dog aspirin.

“They just off-handedly mentioned they were giving ‘doggie aspirin’,” she recalled. “They didn’t know what the dosage was or who the manufacturer was. They said they got it at a Wegmans supermarket. They said it did not work, but they had been giving it sporadically, not consistently.

“I advised them to stop immediately, and I would get them on a more appropriate medication that not only works better but is safer,” Abramo added.

Abramo visited the Wegmans supermarket where her clients said they had purchased the aspirin, and she found it in the pet supplies aisle. She spoke with the store manager and voiced her concern. A few days later, she heard from an the chain's headquarters and learned that the store planned to stop selling dog aspirin.

“Frankly, it wasn’t selling at all,” Jo Natalie, a Wegmans spokeswoman, told the VIN News Service (VNS). She cited slow sales as the reason it was being discontinued.

The VNS queried a number of stores in Sacramento, Calif., and found that canine aspirin was not sold in two chain grocery stores or a pharmacy. However, it was sold in two pet stores visited. Both stores carried a single brand, though online searches for the product show at least eight different labels of dog aspirin available.

Reviews from dog owners about their experiences with giving dogs aspirin posted on 1-800-PetMeds, billed as "America's largest pet pharmacy," are all positive.

One owner wrote in an online review that aspirin “works for our dog, the other pain medications from the vet made him very sick. This is the best purchase ever because it keeps our dog up and moving.”

Dr. Michael Dym, a New Jersey-based homeopathic veterinarian, wrote on the site that he finds aspirin as effective and cheaper than other, newer drugs. He noted that he often directs owners to give it at a much lower dose than the 10 mg per pound that is often recommended.

Janet Tobiassen Crosby, DVM, has addressed the use of aspirin in dogs in her posts on About.com, a Web site designed to lend "expert guidance" to people searching the Internet.

Crosby stated online that aspirin may be recommended to ease pain in an arthritic pet as long as it's used “with caution and under veterinary supervision.” She mentioned that it should not be given to pregnant animals because it might cause birth defects. She also noted that it can interact with other drugs, including cortisones, digoxin, some antibiotics and furosemide.

Yet in a recent VNS interview, the veterinarian expressed an even more conservative approach to giving dogs aspirin. She explained that she wrote the online guidance for aspirin in the late 1990s, before many of the newer analgesics were commonly used. Nowadays, Crosby does not get many questions about aspirin, she says. 

Dr. Mark G. Papich, a professor of clinical pharmacology at North Carolina State University’s College of Veterinary Medicine has written review articles about NSAID analgesia, and he does not take lightly the fact that aspirin is being marketed for dogs.  

He explained that because aspirin is allowed by the U.S. Food and Drug Administration for human use, companies do not need any other specific approval to market it for dogs. He added that marketing it to the public works against incentives to get better NSAID drugs researched and approved.

“It is unfortunate,” he said. “The companies that are doing this are getting away with something.”

Papich also said that dosing aspirin for dogs is difficult because they metabolize it differently from humans. The dog might have side effects, or worse, be under-treated and not experience any relief, he said.

“Either one might dissuade (owners) from seeing their veterinarian,” Papich said.

The indiscriminate use of an over-the-counter drug such as aspirin might mask signs of more serious disease, such as osteosarcoma, making it more difficult to get an early diagnosis, noted Dr. Mark Grossman, a VIN toxicology consultant and practice owner in Manto, N.C. Detecting malignancy of the bone would require a proper workup by a veterinarian and call for analgesic therapy — something a dog isn't likely to get when its pain is being treated solely at home.

"Another huge problem with aspirin is it needs a very long wash-out period before switching to one of the approved NSAIDs for dogs," he added.