By Matthew Kearns, DVM
“My dog ate three grapes (or raisins). Should I be worried?” We get a phone call like this at least once every week to every other week. That’s a good question because we, as a veterinary community, are still looking for the exact answer. Let’s take a closer look at grape and raisin toxicity to see if we can shed some light on what we do know about this nebulous topic.
What portion of the grape or raisin is toxic? Unfortunately, the exact toxic substance to dogs in grapes and raisins is still unknown. Neither the color of the grape, nor seeded versus seedless makes a difference. As a matter of fact, the one portion of the grape that has been ruled out as a cause of kidney damage is the seed or grape seed extract.
Theories arise as to which component of the grape is toxic. Some experts feel that high concentration of a type of sugar component called monosaccharides, whereas others blame a compound called tannins.
Additional theories do not implicate anything in the grape itself, but rather the growth of certain fungi on the grape and toxins produced called aflatoxins, or pesticides sprayed on grapes. More recent evidence points toward something in the meaty portion of the grape or raisin because veterinary toxicologists found that raisins that have been cooked (in cookies, breads, cakes, etc.) are less toxic than grapes or uncooked raisins.
How much is too much? This answer is also unclear. There does seem to be a genetic component associated with which individual dogs are more sensitive to grapes or raisins.
An article published in 2009 reviewed the charts of almost 200 dogs over a 13-year period. The study found some dogs ate over two pounds of raisins without developing any signs of poisoning, whereas others developed irreversible kidney failure with as little as 3 grams of grapes or raisins.
Just to give you some perspective as to how much 3 grams is: Your average grape weighs 5 grams, and a raisin weighs about 0.5 gram. As little as one grape or six raisins could be toxic to your dog. However, some dogs will not get sick or require large amounts of grapes/raisins before any damage is done.
Is there an antidote to this type of poisoning? The short answer is no. This is truly an example of “an ounce of prevention is worth a pound of cure.”
The patients that did better in the same 2009 study were those in which the owners witnessed the ingestion and brought them to a veterinary clinic immediately. The veterinarians were able to induce emesis (force vomiting) and give activated charcoal ASAP. Patients that were already showing symptoms of toxicity such as lethargy, loss of appetite, vomiting and increase in thirst/urination were less likely to make a full recovery.
In conclusion, veterinarians are still not sure as to what portion of the grape/raisin is poisonous, nor which dogs are more sensitive to grapes/raisins. Therefore, keep grapes and raisins away from your dog when possible and, if you witness your dog eating grapes or raisins, bring him or her immediately to your veterinarian’s office or an emergency clinic for treatment.
Dr. Kearns practices veterinary medicine from his Port Jefferson office and is pictured with his son Matthew and his dog Jasmine.