Between 1999 AND 2001, 10 dogs were reported to the ASPCA Animal Poison Control Center (APCC) because of acute gastrointestinal
and renal toxicosis after they had ingested large quantities of raisins or grapes.1 The grapes ingested included fresh grapes of both red and white varieties from grocery stores or vines in private yards and
fermented grapes from wineries. The raisins ingested were various brands of commercial sun-dried raisins. Initially, it was
thought that imported grapes were the culprit, but it was later determined that domestically grown grapes were just as likely
to cause toxicosis.2
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In the cases reported, the estimated amount of ingested raisins or grapes ranged from 0.41 to 1.1 oz/kg.1 Because 4 lb of grapes equal about 1 lb of raisins, fewer raisins need to be ingested to reach toxic levels. In July 2004,
the ASPCA APCC issued a nationwide alert stating that raisins and grapes can be toxic to dogs.3 The alert reported that about 50 dogs had exhibited problems ranging from vomiting to life-threatening renal failure or had
died after they had ingested varying amounts of raisins or grapes. Because there are still many unknowns about the toxic potential
of grapes and raisins, the ASPCA APCC has advised that grapes or raisins not be given to pets in any amount.3
In this article, I describe the grape-raisin syndrome in dogs and review the basic steps in treating the most life-threatening
aspect of this toxicosis—acute renal failure.
Proposed mechanism of action
The toxic mechanism of action for grapes and raisins is unknown. It is not clear whether the risk of toxicosis is the same
with cumulative doses as with large, acute, or single ingestions. It is also uncertain whether some dogs are more susceptible
than others because of differences in metabolic enzymes or genetic predisposition.4 No known reports of grape toxicosis exist in other species. The amount of grapes or raisins that must be ingested to cause
renal toxicosis remains unknown despite ongoing studies.
Several possible mechanisms for the toxicosis have been suggested including: 1) a nephrotoxin in the grapes and raisins; 2)
fungicide, herbicide, or pesticide contamination of the grapes and raisins; 3) heavy metal contamination; 4) high concentrations
of vitamin D; and 5) fungus or mold contamination of the fruit.1 To date, suspect grapes and raisins have been screened for various pesticides, heavy metals (such as lead and zinc), and
mycotoxins, but all results have been negative.1,5 In cases in which affected dogs ate grapes grown in private yards, owners confirmed that no insecticides, fertilizers, or
antifungals had been used on the fruit. A nephrotoxin or an idiosyncratic reaction leading to hypovolemic shock and renal
ischemia has been proposed; however, this mechanism has not been proved to be the cause of the renal failure.6 Excessive sugar ingestion through grapes or raisins has also been discussed as potentially causing shock to the homeostasis
system or to excretory function but has not been proved.7
Histologic findings in several cases have included renal tubular necrosis, metastatic mineralization of numerous tissues,
and evidence of renal tubular epithelial regeneration.4 Until more information about the pathophysiology is available, it seems prudent to recommend that dogs known to have ingested
large quantities of grapes or raisins be treated for a potentially toxic ingestion to prevent the onset of acute renal failure.1-3
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