Grape and raisin toxicity: Grape Expectations

Pressley, the cocker spaniel on our exam table, had been vomiting and lethargic for two days.  We do our best to find out if our vomiting patients have eaten something unusual, but this dog’s owner insisted that he was always walked on a leash and couldn’t possibly have eaten anything without her knowledge.  “All he gets besides his food and his treats are grapes — he loves them!” she said.

Although the danger of grape (including some currants) and raisin ingestion has been known for over a decade, not every dog owner has gotten the message.  It’s not clear at this time whether other species are affected. 

A dog can develop vomiting and diarrhea within a few hours of eating raisins or grapes.  The dog might also present with weakness, increased water drinking, not eating, or a painful abdomen.  The kidneys take a hit, and renal failure can develop within 48 hours of ingestion.  Veterinarians diagnose the toxicity by taking a careful history and administering blood tests to reveal any increases in kidney values. 

If ingestion has occurred within a couple of hours, inducing vomiting might help decrease the amount of toxin that is absorbed.  Further treatment for raisin and grape ingestion is mostly supportive:  Activated charcoal, IV fluids for 36 to 72 hours, drugs to prevent vomiting, and H2 antagonists (Pepcid is an example) are all helpful.   Such early treatment is likely to help regenerate the damaged kidneys and aid in recovery.  But the prognosis for pets that aren’t treated, or that are seen at a later stage when renal failure develops, can be grave.

When I was a child, we had a beloved English springer spaniel named Nipper.  He was a master at jumping and snatching a grape in midair with a loud clack of his teeth.  Nipper scarfed down many clusters of grapes during his 14 years on earth.  Why didn’t he develop grape toxicity and kidney failure, and die?  Because grape and raisin toxicity is puzzling!  It appears that not all dogs are susceptible to the poisoning by the fruit. 

Another curious thing about this toxicity is that nobody is quite sure what the offending substance is in grapes.  It's also not known exactly what part of the grape contains the toxin.  Wine and grape juice are not toxic, so it’s not in the juice.  It’s also not in the seeds, because both seeded and seedless varieties cause problems, and grape seed extract appears to be safe. To complicate matters, nobody really knows the toxic dose, but when you consider the many types of grapes, perhaps that isn’t surprising.  There are data on the lowest recorded amounts of the fruit that cause kidney failure.  I calculated that as few as two raisins or two grapes per pound of dog could be a toxic dose.

    

The calls we receive from dog owners regarding grape or raisin ingestion can present a dilemma.  Some cases are clear cut: a 10-pound Yorkie ate two snack boxes of raisins.  But Pressley the cocker didn’t have grape toxicity — turns out it was just an upset stomach.  And my Nipper lived to a ripe old age.   We still don’t know the risk factors for any given pet. 

The owner of a dog that ate the fruit and is acting normal might understandably be hesitant to spend hundreds of dollars on supportive care, but any significant exposure should be treated.  It might mean a lighter wallet, but it could also mean a live dog with normal kidney function.