What Could it Hurt?

Geoffrey has an upset tummy, vomiting (oh no, not THAT subject again!) a bloody fluid and turning down all the food he is offered-even his favorite treats. But that wasn't the problem a week ago when he was playing hard in the snow with his buddy. His owners said he slipped on a patch of ice, yelped, and came up lame on a front leg. They were tired and sore from over-doing it themselves, so thought they knew how he felt. They went to their medicine chest and got out some aspirin-some for themselves and some for Geoffrey. They didn't wrap their own dose in a piece of cheese, however. Geoffrey took his "treat" eagerly and after awhile did start to feel better. He got the aspirin on and off during the week; he was noticeably better with his limping after getting a dose than if they missed giving it for a day. But yesterday he started acting like a sick dog-Geoffrey usually LOVES his food, so turning down treats was a big red flag. When he vomited what looked like blood, they knew they better call us.

Aspirin is a very common medication, found in many homes and used by most humans at one time or another for headaches, joint pain, or fevers. It even comes orange candy flavored in some children's formulations, making this important drug seem very benign-what harm could it cause?

Cyclooxygenase is an enzyme involved in the inflammatory process-aspirin inhibits this and the subsequent production of of an inflammatory chemical called prostaglandin. Arachidonic acid, a fatty acid that is essential in the diet of cats and dogs, makes up cell membranes. When inflammation is present, cells begin to make prostaglandins from their arachadonic acid. Aspirin is a true anti-inflammatory drug as it stops this process.

The problem is that there turns out to be more than one form of cyclooxygenase, and they do not all generate inflammatory prostaglandins. Some prostaglandins have important functions and we prefer not to interfere with these. Aspirin, unfortunately, does not distinguish between different forms of cyclooxygenase and inhibits them all. Because of this, aspirin has largely been replaced in our at-home pharmacies or medicine cabinets by safer medications like ibuprofen (Advil) or acetominophin (Tylenol.) They primarily inhibit the form of cyclooxygenase that is associated with inflammatory prostaglandins. Aspirin is inexpensive and readily available but no longer a leading choice for pain/inflammation relief.

Thromboxane is a prostaglandin that deserves a mention here. It is involved in blood clotting. When a blood vessel is injured, a type of blood cell called platelets accumulate in the area and pile on top of each other, creating a plug or clot. Thromboxane is important for keeping these platelets adhered together, constricting the blood vessel to minimize bleeding and several other more complicated operations that enhance clotting. By inhibiting cyclooxygenase, thromboxane cannot be produced and the platelets present at the time aspirin is given are permanently inactivated. This is how aspirin works to prevent abnormal clots, an important part of treatment for many human heart disease patients as well as the rare pet with abnormal clotting tendencies.

The most common side effect of aspirin is stomach upset. It has been discovered that most dogs get some degree of stomach ulceration, ranging from microscopic to full perforations. Hematemisis (bloody vomit) can result. In humans, nausea has been so common that the numerous alternative pain relievers (Tylenol, Aleve, etc.) are becoming more common. It is important to resist the temptation of using any of these non-aspirin products in pets as most have a far greater potential to ulcerate the stomach than does aspirin. As human pain relieving drugs go, aspirin is probably one of the safer ones; however, as veterinary pain relieving drugs go, aspirin is generally the last choice. Even "Dog Aspirin" commonly found for sale at pet stores is not without its potential for serious side effects.

Dogs and cats are NOT small humans and we have to remember that some medications are metabolized (broken down or utilized by the body) differently in these species than in us.

CATS METABOLIZE ASPIRIN SLOWLY AND IT IS EASY TO OVERDOSE THEM.

Aspirin will reduce blood flow through the kidney, which is likely to make pre-existing kidney disease much worse.

Enteric coating of aspirin may alter the way aspirin is absorbed in an animal's stomach. The pills tend to stick to the stomach lining instead of dissolving properly. If enough tablets accumulate, overdose and death can occur.

We took Geoffrey off the aspirin, of course, and started him on some gut-protectant medications. If he does not improve rapidly, he may need radiographs of his abdomen and/or an endoscopic evaluation of the gastric mucosa (stomach lining) to look for any serious ulcerations (which he undoubtedly has-thus the blood in his vomit) or perforations. Dogs have died from peritonitis or infections in the abdomen as a result of this, and it is a very painful condition. Geoffrey will be fasted for a time, then started on bland food so his gut won't have to work as hard to digest it. If he later needs pain medication for the gastric ulcers, (or for the original lameness problem) we will probably try a narcotic or other drug that won't have the same risk of side effects.

Most of the time you could probably get away with using aspirin on your dog with out any problems, but how awful would you feel if he or she had a reaction (not at all uncommon) like Geoffrey did? So, the moral of the story is:

Do not use human medications on pets without specific instructions on how to safely do so from your veterinarian.

Peace,

DrReneigh