Magoo was a big, playful Labrador retriever who often got himself into some sticky situations. Usually, his escapades were harmless. But one day, he managed to snag a box of raisins from the pantry and ended up eating an entire pound of the sweet treats. Other than being exasperated by Magoo's behavior, his guardians didn't think much about it. They knew that lots of people shared grapes with their dogs and often used raisins as training rewards. So it hardly seemed the kind of emergency that required a call to the veterinarian. In fact, if Magoo's parents had called the ASPCA's Animal Poison Control Center (APCC) just a few years ago, they would have been told not to worry about it.
Through the Grapevine
Enter the APCC AnToxTM database, a computerized system that contains nearly 500,000 animal-related medical conditions and that enables veterinarians to quickly identify toxic-substance exposures, recognize clinical signs and administer proper treatment. By tracking cases in this registry, similarities in animal medical conditions nationwide can be logged and syndromes can be identified.
Around 1999, the APCC began noticing a trend in dogs who had eaten grapes or raisins: Nearly all developed acute renal (kidney) failure. As more cases were reported, enough data was generated in the database to help veterinarians identify and treat dogs at risk. In all of the cases, the ingredients for potential acute renal failure were the same. Whether the ingested grapes were purchased fresh from grocery stores or grown in private yards didn't seem to matter, nor did the brand eaten. And the ingested amounts varied considerably, from over a pound of grapes to as little as a single serving of raisins. The cases weren't from any specific region, but instead came from across the United States.
The database showed that dogs who ate the grapes and raisins typically vomited within a few hours of ingestion. Most of the time, partially digested grapes and raisins could be seen in the vomit, fecal material, or both. At this point, some dogs would stop eating (anorexia), and develop diarrhea. The dogs often became quiet and lethargic, and showed signs of abdominal pain. These clinical signs lasted for several days -- sometimes even weeks.
When medical care was sought, blood chemistry panels showed consistent patterns. Hypercalcemia (elevated blood calcium levels) was frequently present, as well as elevated levels of blood urea nitrogen, creatinine, and phosphorous (substances that reflect kidney function). These chemistries began to increase anywhere from 24 hours to several days after the dogs ate the fruit. As the kidney damage developed, the dogs would produce little urine. When they could no longer produce urine, death occurred. In some cases, dogs who received timely veterinary care still had to be euthanized.
Why did the fruit cause the dogs to become ill? No one knows. Suspect grapes and raisins have been screened for various pesticides, heavy metals (such as zinc or lead), and mycotoxins (fungal contaminants) and so far, all results have come back negative. In the cases where the grapes were grown in private yards, owners confirmed that no insecticides, fertilizers or antifungals had been used on the fruit. A recent theory is that tartaric acid in grapes or raisins may contribute to the kidney damage seen with intoxication, but no studies are available to confirm or refute this theory.
"Raisin" the Success Rate
Even though the exact cause of the renal failure is unknown, dogs who ingest grapes and raisins can be treated successfully to prevent its development. The first line of defense is decontamination. Inducing vomiting in recent ingestions and administering activated charcoal helps prevent absorption of potential toxins. Dogs should be hospitalized and placed on intravenous fluids for a minimum of 48 hours. A veterinarian should monitor blood chemistry daily for at least three days following the ingestion. If all blood work is normal after three days, it's unlikely that kidney failure will occur. If a dog shows evidence of renal failure, fluids must be continued, and other medications should be used to stimulate urine production. Some dogs may need peritoneal dialysis, a process where the peritoneum (the membranes surrounding the abdominal organs) is used to filter waste products that are normally filtered by the kidney.
Thanks in part to the AnTox database, grape or raisin ingestion can be easily identified and treated. Today, a dog can make a complete recovery from this potentially fatal condition.
Dr. Means is a veterinary toxicologist at the ASPCA's Animal Poison Control Center in Urbana, Illinois.