Raisins and grapes: Potentially lethal treats for dogs

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

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

Clinical signs

Clinical signs exhibited by the dogs in cases reported to the ASPCA APCC have ranged from acute gastrointestinal signs (e.g. vomiting, anorexia) to acute renal failure (e.g. oliguria and anuria); death has also been reported. Vomiting occurs in all dogs and begins within the first few hours of ingestion.4 Most affected dogs pass partially digested raisins or grapes in the vomitus, feces, or both. Within 24 hours, the clinical signs observed in dogs include anorexia, lethargy, diarrhea, or abdominal pain.1 These gastrointestinal signs could last for days to weeks. A serum chemistry profile, especially blood urea nitrogen (BUN) and creatinine concentrations, should be evaluated daily for at least three days after grape or raisin ingestion. If the results are normal after three days, it is unlikely that renal failure will develop.2 However, even if the BUN and creatinine concentrations are normal, a serum chemistry profile should be repeated five to seven days later. Abnormalities in BUN concentrations (23 to 209 mg/dl; normal = 5 to 29 mg/dl) and serum creatinine concentrations (4.3 to 18 mg/dl; normal = 0.3 to 2 mg/dl) can become evident anywhere from 24 hours to several days after dogs ingest grapes or raisins.1 Hypercalcemia (serum calcium concentration = 12.3 to 26 mg/dl; normal = 9.3 to 11.8 mg/dl) and hyperphosphatemia (serum phosphorus concentration = 6.4 to 22 mg/dl; normal = 2.9 to 6.2 mg/dl) can also develop 24 hours to seven days after ingestion.1

As tubular damage progresses, dogs can become oliguric to anuric within 24 to 72 hours after ingesting large quantities of grapes or raisins. Fatality in dogs with acute renal failure due to raisins has been reported to be as high as 50% to 75%.5 Concurrent oliguria or anuria in an affected dog is associated with a poor prognosis.6 In two reported cases, dogs that survived their oliguric renal failure showed no evidence of residual renal compromise several months after the toxic insult.4

Treatment

Because of the severity of the renal disease and potential for death, aggressively treat all dogs that have ingested grapes or raisins. In dogs that have recently ingested large quantities of grapes or raisins, it is important to decontaminate the gastrointestinal tract by administering emetics and activated charcoal. Emetics should be used only if the dog is stable, is not having seizures, and is able to protect its airway (i.e. is not comatose and has normal laryngeal function). The various emetics used in veterinary medicine are listed in Table 1.8

Table 1: Emetics Used in Veterinary Medicine

Once emesis is induced, administer activated charcoal. Various preparations are available, including a dry powder, granules, and a liquid suspension. Repeated administration of activated charcoal every four to six hours is beneficial in managing toxicoses because it interrupts enterohepatic recycling. The dose of activated charcoal is 1 to 4 g/kg suspended in liquid.8 It is best administered through a stomach tube.8

Maintaining renal perfusion is extremely important in preventing the progressive decline in glomerular filtration rate and onset of renal failure. Hospitalize asymptomatic dogs, and give them a balanced electrolyte solution intravenously at a maintenance rate for at least 48 hours. Closely monitor the dog's renal function, including BUN and creatinine concentrations and urine output, over 72 hours after grape or raisin ingestion. Dogs with anuric or oliguric renal failure should receive aggressive fluid therapy to help restore renal perfusion and electrolyte and acid base balance. Diuresis may also be beneficial in reducing the amount of time the renal tubules are exposed to the toxic principle.4

Summary

Until information on the pathophysiology and specific treatment of grape and raisin toxicosis becomes available, it is best to contact the ASPCA APCC (888-426-4435) when a case arises. The ASPCA APCC has specially trained staff who provide assistance to pet owners and specific diagnostic and treatment recommendations to veterinarians. Because affected dogs could die, instruct owners to stop feeding their dogs grapes, raisins, and any food containing grape extracts. If ingestion should occur, advise owners to seek veterinary assistance immediately to initiate aggressive medical management. For more information on the toxicity of grapes or raisins, see the ASPCA APCC Web site (www.apcc.aspca.org).

Brandy Porterpan, DVM

Department of Small Animal Clinical Sciences

College of Veterinary Medicine

Texas A&M University

College Station, Texas 77843

REFERENCES

1. Gwaltney-Brant S, Holding JK, Donaldson CW, et al. Renal failure associated with ingestion of grapes or raisins in dogs. J Am Vet Med Assoc 2001;218:1555-1556.

2. Means C. The wrath of grapes. Available at: www.vin.com/Members/SearchDB/misc/m05000/m02410.htm. Accessed April 2005.

3. Animal Poison Control Center. ASPCA Animal Poison Control Center issues a nationwide update: raisins and grapes can be toxic. July 6, 2004. New York, NY: American Society for the Prevention of Cruelty to Animals.

4. Mazzaferro EM, Eubig PA, Hackett TB, et al. Acute renal failure associated with raisin or grape ingestion in 4 dogs. J Vet Emerg Crit Care 2004;14:203-212.

5. Stokes J, Forrester SD. New and unusual cases of acute renal failure in dogs and cats. Vet Clin North Am Small Anim Pract 2004;34:909-922.

6. Penny D, Henderson SM, Brown PJ. Raisin poisoning in a dog. Vet Rec 2003;152:308.

7. Singleton V. More information on grape or raisin toxicosis. J Am Vet Med Assoc 2001;219:434-436.

8. Rosendale ME. Decontamination strategies. Vet Clin North Am Small Anim Pract 2002;32:311-321.