Both grapes and raisins are commonly found in the daily diets of humans. Raisins are considered by many to be a great snack for toddlers, and table grapes are served with cheese, packed in school lunches, and are a nice accompaniment to many meals. They come in many forms including grape juice, grape jelly, and let’s not forget wine. These foods are also commonly found in baked goods like breads and cookies, and in breakfast cereals. It’s hard to imagine how something so commonly enjoyed by humans can be harmful to dogs. But it is!!
The toxicity of grapes and raisins remains somewhat of a mystery to toxicologists. But what we do know is that both grapes and raisins are toxic to dogs. The exact toxic component is not currently understood, so it is assumed that all products containing grapes or raisins are potentially toxic to dogs. It does not appear that they are toxic to any other species, though some believe that they may also be toxic to cats.
Along with not knowing what the exact toxic component is, we also do not know exactly how many grapes or raisins are toxic to dogs. Some reports have shown as few as 4 or 5 grapes have resulted in toxicity, and as little as about 1 ounce of raisins for a dog weighing 22 lb (10 kg.) One report has also revealed that about 75% of dogs that experienced toxicity did so after eating raisins as opposed to fresh grapes. So it appears that whatever the toxin might be, it is probably concentrated when grapes are dried into raisins.
So what could the toxin be? One possibility is a mycotoxin. Mycotoxins are a class of toxin that come from molds. As molds grow on grains and fruits, they produce secondary metabolites called mycotoxins. They probably help provide nutrients to the mold or help it to proliferate. Most molds and algae produce these secondary metabolites, and many are not harmful. But some are among the most toxic substances on earth. What makes them difficult to manage is that even when visible signs of mold are gone, the mycotoxin can persist in the food item. They can occur in growing grains and fruits, or after they have been harvested and are in storage. There is a mycotoxin called ochratoxin that is known for causing the same effects we see with grapes and raisins. But attempts to find it consistently in cases of toxicity have not been successful. It is possible, however, that a not-yet-identified mycotoxin is infecting grapes and raisins and is the culprit.
Other possibilities that are being considered are a sensitivity by certain dogs to tannins which are found in grapes and raisins, and a sensitivity to the complex sugars that are found in them. The bottom line though is that dogs should not have access to grapes or raisins.
The kidneys are the target organ for toxicity. Initially after exposure dogs may develop diarrhea. Within a day or two after ingestion signs of kidney failure develop. At first this manifests by dogs drinking and urinating more than normal. As the kidney failure progresses, the dog will produce less urine, will lose its appetite, and may have frequent vomiting. Without treatment the dog will die. Therefore it is vital that dogs exposed to grapes and raisins be seen by a veterinarian urgently. Data from exposures shows us that dogs that present to the veterinarian within 24 hours of exposure have good outcomes with treatment. Those that present after 2 to 3 days often die even with treatment. There is no antidote but the veterinarian will institute therapies that support the kidneys and administer fluids to help hasten elimination and protect the kidneys.
As I always say, prevention is key. Do not ever give your dog grapes or raisins, and if you keep these in your home, always store them in closed containers in places that dogs cannot access on their own. Keep grapes in the refrigerator and only take them out when they will be eaten right away. Do not leave them unattended on a countertop. Keep raisins in closed containers in high cabinets. If you have small children in the home and regularly give them raisins as snacks, make sure that the dogs are safely contained in other parts of the home or yard while the children are snacking. And educate your kids to never feed dogs raisins.
This is Dr. John Tegzes, the Toxvet, wishing you a poison-free day!
John H. Tegzes, MA, VMD, Dipl. ABVT
Dr. John Tegzes is a veterinarian who specializes and is board-certified in Toxicology. He graduated from the School of Veterinary Medicine at the University of Pennsylvania, and completed residency-training in diagnostic and clinical Toxicology in the Vet School at the University of California, Davis. He has worked as a veterinarian in companion animal practices in Portland, OR, and in Toxicology at the Oregon Poison Center and the California Poison Control System. Currently he is a Professor of Toxicology in the College of Veterinary Medicine at Western University of Health Sciences in southern California. He resides in Los Angeles, California in the happy company of two dogs, two cats, and a sun conure.