New Research Shows that Grapes & Raisins Can be Deadly When Consumed by Dogs

Source: PetWave, Updated on August 30, 2016
Grape and Rasin Toxicity
Grape & Raisin Toxicity Guide:

Grape and Raisin Toxicosis – Definition

Most of us know what grapes are: they are a small, round-to-oval, thin-skinned fruit that grows on a vine. Grapes are members of the plant genus, Vitis. Raisins are simply dried or shriveled-up grapes, after the grapes’ moisture content has been reduced to about 15% of normal. Raisins can differ dramatically in color due to the type of grape and the different drying processes used. Most black or very dark purple-ish raisins have been dried in the sun. Lighter brown raisins usually have been mechanically dried or dehydrated, while yellow to golden raisins typically are dehydrated mechanically and then treated with sulfur dioxide. “Toxicosis” means any disease condition that is caused by poisoning. Therefore, our pet dogs that are suffering from grape and raisin toxicosis have basically been poisoned by eating these fruit products. There are also reports of dogs having been poisoned by eating currants, which are dried fruits in a similar family.

Grape and Raisin Toxicosis – Causes

Reports of dogs being poisoned by eating grapes and raisins really surfaced in the mid-to-late 1990s. Cats and ferrets may also be adversely affected by ingesting these products, but so far these reports are only anecdotal and haven’t been scientifically confirmed. Grapes and raisins are not toxic to every dog, or to all dogs in the same amounts. In fact, there doesn’t seem to be a well-documented relationship between the amount of fruit a particular dog eats (which is called the “exposure dose”) and the severity of its toxic reaction. However, when poisoning does occur, it often is related to ingestion of fresh grapes of any color or size from grocery stores, field or private storage containers or from grape crushings, fermented grapes from wineries and raisins being processed (or already processed) for commercial distribution. The amount of grapes or raisins that will be poisonous in a given animal cannot be predicted. Scientific reports have noted that toxic and potentially deadly doses of raisins range from 0.16 to 0.7 ounces per kg of the dog’s body weight, and 4 to 5 grapes have been reported as being toxic to an 8.2 kg dog. One kilogram is equal to 2.2 pounds. So, these are not very large amounts of the fruit to be dangerous to our pets.

Why grapes and raisins can be so poisonous to dogs still is not understood. Some suggestions are that there may be pesticide residues or fungal toxins on the outside of the fruit itself that contribute to toxicosis in dogs. However, homegrown grapes, organically-grown grapes, grapes with seeds and grapes without seeds all have been shown to be nephrotoxic (cause kidney damage) in dogs. Interestingly, grapeseed extract apparently has not been associated with nephrotoxicity. The onset of clinical signs is usually fairly sudden after the dog has eaten the fruit. The toxins probably are processed and filtered by the dog’s kidneys and then excreted in its urine, as long as the dog’s kidneys are still able to produce urine despite its disease.

Grape and Raisin Toxicosis – Prevention

The only way to prevent dogs from becoming ill from grapes and raisins is to keep them from eating these fruits. Raisins are roughly 4.5% more concentrated than fresh grapes on a per-weight basis. Owners should never feed raisins or grapes to their dogs. There are many other, more palatable and much safer treats that can be fed, including so-called “cookie bones,” carrots, bananas and other healthy items. Even though up to half of the dogs may not get sick from eating grapes or raisins, why take the risk? It just isn’t worth it.

Grape and Raisin Toxicosis – Symptoms and Signs

Owners of dogs who have become intoxicated by eating raisins and/or fresh grapes may notice many different signs, most of which could be attributed to eating a number of other toxic things. Still, the syndrome of poisoning in dogs tends to follow a similar course, regardless of the toxin, with the main differences being in how suddenly the animal gets sick, and then how sick it becomes. Grapes and raisins can cause one or more of the following symptoms in domestic dogs:

  • Nausea; abdominal pain
  • Vomiting (usually within 24 hours of eating the fruit; may occur within a matter of a few hours; fairly consistently the first clinical sign)
  • Partially digested grape and/or raisin parts in the vomitus
  • Loss of appetite (inappetance; anorexia)
  • Diarrhea
  • Partially digested grape and/or raisin parts in the stool
  • Lethargy; dullness
  • Weakness
  • Lack of coordination (ataxia)
  • Dehydration
  • Decreased volume of excreted urine (oliguria; reduced daily output of urine)
  • Complete suppression of urine formation by the kidneys (anuria; very serious)

These signs can last from days to weeks after the dog has eaten the fruit. In severe cases, when the signs progress to a complete absence of urine formation and excretion, the dog may be in a potentially irreversible and fatal situation.

Grape and Raisin Toxicosis – Dogs at Increased Risk

There is no reported age, gender or breed predisposition to developing grape or raisin toxicosis. However, dogs that already are suffering from kidney damage or disease may have an increased chance of developing acute renal failure from eating raisins and/or grapes.

Grape and Raisin Toxicosis – Diagnosis

When a veterinarian sees a dog showing generalized size of poisoning, she of course will try to determine from the owner and from physically examining the animal what the source of toxicity is. Routine blood and urine tests typically will reflect acute onset of kidney (renal) failure in dogs suffering from grape or raisin poisoning. This frequently includes elevated levels of creatinine, calcium, phosphorus, phosphate and nitrogen in their blood samples. Because the underlying cause (on a microscopic level) of grape and raisin toxicity in dogs still is not known, there is no reliable confirmatory test for this condition. Abdominal radiographs (belly X-rays) and ultrasound may be taken to look at the size and structure of the kidneys, and kidney biopsies can be taken to assess the nature and extent of renal damage. However, these tests are not routinely done, other than perhaps to assess the animal’s prognosis. Diagnosis of grape and raisin poisoning typically is made based on the dog’s history, clinical presentation and the post-mortem pathological evaluation of its kidneys during a necropsy, which is the name for an autopsy done on animals after their death. These diagnostic options may not offer owners a great deal of comfort, but further research is always underway.

Grape and Raisin Toxicosis – Treatment

Dogs thought to be suffering from grape or raisin toxicosis should be treated extremely aggressively. Treatment usually involves decontamination to remove its remaining stomach contents in order to prevent further absorption of toxic substances. This can be done by stimulating vomiting (emesis) with drugs, pumping the stomach (gastric intubation and lavage) and/or administering activated charcoal, which is a substance that tends to bind to toxins and prevent them from being absorbed by the gastrointestinal tract. Aggressive intravenous fluid therapy is also often strongly recommended for at least 3 days after the grapes or raisins were ingested, and probably for longer, although the dog’s central venous pressure and overall urine output must simultaneously be monitored to prevent the possibility of fluid overload. A number of other medications can also be considered to help with a dog’s vomiting, diarrhea, nausea, dehydration and related symptoms.

Grape and Raisin Toxicosis – Prognosis

The outlook for dogs whose grape or raisin toxicosis has progressed to the stage of impaired or nonexistent urine production is guarded to poor. The kidneys of these animals unfortunately may have been damaged beyond repair due to the acute renal failure associated with grape and raisin poisoning in many dogs. To have a chance of survival with a good quality of life, these dogs may need extensive, aggressive and prolonged dialysis, fluid administration and inpatient supportive care. Many local clinics aren’t set up to provide this degree of continuous care, and the owner may be referred to a veterinary teaching hospital or specialized referral center to pursue potential treatment options.

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