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Within the last couple of years, the Animal Poison Control Center (APCC) in Urbana, IL has documented multiple cases of grape and raisin poisoning in dogs. Presumably, this has occurred for years, but sporadic cases seen by individual veterinarians have probably been discounted and written off to some other cause of renal problems. By documentation of cases in their database, the APCC was able to establish a correlation between renal problems and grape or raisin ingestion by dogs.
The source of the problem has been varied. Red, Concord or white grapes obtained in grocery stores or home-grown have all been implicated. Raisins typically are made from Thompson seedless white grapes. Other possible types of raisins are probably also toxic, but haven't been named in case reports. Chocolate covered raisins should also be considered potential renal toxicants.
The toxic principle in either grapes or raisins is unknown. Tannins are present primarily in grape peels. The peels are still a part of raisins. However, only low to moderate amounts of tannins are present in grapes or raisins compared to acorns, a known renal toxicant in large animals. Whether or not tannins or their metabolites are involved in grape/raisin toxicosis in dogs is unknown. Grapes or raisins lack significant amounts of vitamin D, which is another recognized renal toxicant. It is unlikely that a pesticide residue is associated with the toxicosis because of the variety of types of grapes and sources of grapes involved. Since the toxic principles is unknown, the mechanism of action is also unknown.
So far, the vast majority of grape and raisin toxicosis have been in dogs. Based on APCC calls, the minimum toxic dose of grapes in dogs is approximately 0.3 oz/kg body weight. This would correspond to about most of their water content. The minimum toxic dose of raisins is approximately 0.1 oz/kg body weight. This would correspond to about 6 raisins/kg body weight. Feeding grapes or raisins to cats or ferrets should also be discouraged because the APCC has received a few calls of similar poisonings in these species.
Onset of clinical signs is usually within 6-24 hours after ingestion with 12 hours being about average. Initial clinical signs are typically GI followed by renal problems. Vomiting is usually the initial clinical sign. Other potential clinical signs include diarrhea, depression-lethargy, anorexia, colic, dehydration and oliguria/anuria. The course of the toxicosis may last from several days to 3 weeks. Dogs that have renal problems have a guarded to poor prognosis.
Diagnosis is made by a history of recent exposure and compatible clinical signs. Renal clinical pathology indices are increased. Typically, serum has increased levels of BUN, creatinine, phosphohrus and potassium. Sometimes calcium is also increased in the serum. The urine will have hyaline casts and will be either hyposthenuric or isosthenuric (S.G. 1.006-1.010).
Treatment is based on alleviating further absorption, if appropriate, and maintaining urine excretion and electrolyte balance. If grapes or raisins have been ingested in toxic amounts within the last 2.3 hours, an emetic may be used followed by activated charcoal combined with an osmotic cathartic. The animal should be given isotonic saline IV at twice the maintenance rate for 48 hours. Metoclopramide, furosemide, dopamine or peritoneal dialysis may be needed for some cases.
Dennis J. Blodgett, D.V.M., Ph.D
VA-MD Regional College of Veterinary Medicine
Blacksburg, VA