Last month, we discussed a toxicity that mainly affects cats (lilies). In this month’s article, the focus is on a toxin that seems to target dogs, found in grapes and raisins. Both interesting and concerning, there is a lot that is unknown about grape toxicity in dogs. Not all dogs seem to be affected, and the dose that can cause problems doesn’t always seem to be the same either.
For over 20 years, veterinarians have observed kidney failure in dogs following grape and raisin ingestion. This reaction occurs from both seeded and seedless grapes. Toxicity has not been reported from grape juice or wine ingestion, but it is still unknown whether those products have toxic potential. Likewise, grapeseed extract has so far not been associated with toxicity.
The toxic principle in grapes/raisins has not been confirmed. Studies have investigated heavy metals, fungal infections and pesticides to no avail. More recently, tartaric acid has been implicated. Tartaric acid is found in cream of tartar, tamarinds, as well as grapes. Dogs ingesting cream of tartar and tamarinds have been found to develop kidney failure similar to the kidney failure that dogs develop after ingesting grapes. Furthermore, tartaric acid levels are not consistent in all grapes, which possibly reveals why some dogs are affected while others are not.
The amount needed to cause kidney damage is also not straightforward. Veterinarians have seen toxicity with as little as 0.3 ounces of grapes per pound of dog, although it’s likely the amount is even lower. This means a 20 pound dog could develop toxicity with 6 ounces of grapes (about 35-40 grapes). With raisins, it is lower - just 1 ounce of raisins could affect a 20 pound dog.
There is no specific test for grape/raisin toxicity. Dogs typically present with vomiting, decreased or no appetite, and increased urination. Lab work reveals elevated kidney values as the most consistent finding. The clinical signs, lab work findings, and history of ingestion (if known), allow for the diagnosis of this toxicity. Toxicity tends to occur relatively quickly – signs can develop within a couple of hours and lab work changes can occur within 12-24 hours, but may take up to 72 hours.
Treatment focuses on rapid decontamination – vomiting is induced if the dog is not already vomiting, and activated charcoal is typically administered in hopes to bind remaining toxins. Then, dogs are given fluid therapy to try to treat the acute kidney damage that has occurred. They require at least several days of hospitalization and frequent lab work monitoring to track their progress. Unfortunately, the prognosis is quite poor if kidney failure occurs and even worse if dogs stop producing urine altogether. Dogs often succumb to the disease within 5 days of ingestion. However, if decontamination and fluid therapy is initiated early, the prognosis is better. Therefore, if you think your pet ingested grapes or raisins, getting them to the veterinary hospital as soon as you can will be the best chance at survival.
While this is a toxicity that seems to target dogs, it is important to point out that anecdotally, cats and ferrets have been suggested to be susceptible. Therefore, it is best not to feed grapes/raisins to these pets as well.