Back in 2001, the first case report of raisin toxicity in a dog was published.  Ever since, raisins and grapes (and all foodstuffs containing them) have been on a no-go list for dog owners. Even a small amount can cause acute kidney injury so complete avoidance is advised. The toxic dosage appears to differ between individuals and dosage does not appear to correlate well with severity of clinical signs. 
The causative agent within the raisins and grapes had not been identified- with investigations into the possibility of mycotoxin contamination or pesticide residues on the fruit being the culprit.
A case study report in the Journal of Veterinary Emergency and Critical Care has linked the renal injury noted in a dog following ingestion of home-made playdough containing tartaric acid to similar cases post-ingestion of tamarind fruit, raisins and grapes.  These fruits are known to contain comparatively high levels of tartaric acid.
Tartaric acid is a plant-based organic acid and the most abundant sources are grapes and tamarinds.  The tartaric acid is found in these fruits in the form of potassium bitartrate and the amount of this salt increases as the grape ripens.  Dogs have a unique sensitivity to tartaric acid not observed in other species including humans or cats.
It is important for clinicians to be aware that tartaric acid is also frequently used in pharmaceuticals, foodstuffs including tamarind paste, cosmetics and in homemade playdough craft recipes.
Following ingestion of the toxin, regardless of the ingredient, the most common clinical signs of raisin/grape toxicity are:
- Vomiting and diarrhea.
- Decreased urine output.
- Abdominal discomfort.
- Neurological symptoms- including ataxia and seizures.
Initial treatment in these cases is symptomatic and aimed towards protecting and minimizing kidney injury. Aggressive fluid therapy should be started as soon as possible. If ingestion was observed, gastric emptying and lavage may assist. Raisins absorb fluid in the stomach, increasing their size and slowing digestion and gastric emptying- it may be worthwhile to induce emesis even several hours post ingestion.  Activated charcoal administration may help to limit absorption of any tartaric acid that remains.
In a retrospective study of 43 cases published in 2005, 47% of cases resulted in patient death or euthanasia.  The mean time post ingestion to presentation at the clinic was 2.8 days.
The renal and neurological signs in this toxicity may be reversible if treatment is aggressive and successful. The presence of neurological signs and decreased urine production on presentation is a poor prognostic indicator. 
Laboratory findings include azotaemia, hypercalcaemia and hyperphosphataemia. Histopathology reports in these cases consistently demonstrate severe renal tubular degeneration, necrosis and tubular mineralization.
In the latest study comparing tartaric acid ingestion, all the dogs began to vomit within 1-14 hours after consumption, considered the most common symptom of raisin toxicity. [3, 4] Azotaemia was noted on bloodwork from 18-53 hours post toxin ingestion. The histopathological results from 3 cases indicated similar changes- moderate to severe renal tubular degeneration, with necrosis, cellular debris and mineralization of basement membranes.
Knowing the causative agent will hopefully raise awareness and educate pet owners to act quickly and may in time allow for more targeted treatment.
1. Gwaltney-Brant, S., et al., Renal failure associated with ingestion of grapes or raisins in dogs. Journal of the American Veterinary Medical Association, 2001. 218(10): p. 1555-1556.
2. Eubig, P.A., et al., Acute Renal Failure in Dogs After the Ingestion of Grapes or Raisins: A Retrospective Evaluation of 43 Dogs (1992–2002). Journal of Veterinary Internal Medicine, 2005. 19(5): p. 663-674.
3. Wegenast, C.A., et al., Acute kidney injury in dogs following ingestion of cream of tartar and tamarinds and the connection to tartaric acid as the proposed toxic principle in grapes and raisins. Journal of Veterinary Emergency and Critical Care, 2022. 32(6): p. 812.
Written on April 6, 2023