Think grapes may be nutritionally good for your dog? Guess again! Raisins and grapes may be part of a nutritionally complete diet for people but can result in acute renal failure in susceptible dogs. The consumption of 11 to 30 grams of grapes per kilogram of body weight will result in clinical signs of toxicosis, and around 32 grams per kilogram will result in renal (kidney) damage. The number of raisins required to induce toxicity will be even less, requiring a dose of only 0.16 to 0.7 oz of raisins per kilogram of body weight resulting in toxicity. In a 2004 report, only four to five grapes were found to be toxic in an 8.2 kg dog. There does not appear to be a clear-cut dose-response relationship which implies some variation in the sensitivity of the individual to the development of the toxicity.

The toxin and mechanism of action have not yet been identified. Potentially toxic substances include ochratoxin, flavonoids, tannins, polyphenolics, and monosaccharides, all which have been theorized to be the cause of the toxicity.

Vomiting occurs one to three hours after ingestion followed by anorexia (not eating), severe abdominal pain, and diarrhea. Additional clinical signs include weakness, tremors (shivering), polydipsia (increase in thirst), and dehydration. Partially digested grapes or raisins may be seen in the vomit or feces. As the toxicity progresses, central nervous system depression occurs as well as a decrease in urine output. Early serum chemistry analysis may include transient elevations in glucose, liver enzymes, pancreatic enzymes, and serum calcium. Serum chemistry analysis 24 to 36 hours after ingestion is consistent with acute renal failure resulting in severe elevations of BUN, creatinine, and serum phosphorous.

When a significant serving of grapes or raisins has been consumed, vomiting may be induced to evacuate the offending substance followed by oral administration of activated charcoal to limit absorption. If twelve hours have transpired since ingestion, treatment should be aggressive with intravenous fluids or peritoneal diuresis in anuric (dogs that cannot produce urine) animals. Clinical signs of toxicity may last from a few days to many weeks. Prognosis is good when treated before kidney failure develops. Once anuric renal failure develops and peritoneal diuresis is implemented, prognosis is poor, often resulting in death or euthanasia.


References:

Ettinger, Stephen DVM, and Edward C. Feldman DVM. Veterinary Internal Medicine. 6th Edition. Elsevier Inc. 2005. Pp. 250-251.

Kahn, Cynthia, ed. The Merck Veterinary Manual. 9th Edition 2005. p. 2364.

Peterson, Michael DVM and Patricia Talcott DVM. Small Animal Toxicology. Saunders Co. Pp. 727-731.