Grapes, Sultanas, and Raisins
When to visit the vet?
Urgent see a veterinarian within 24 hours
If the condition worsens / symptoms persist, consult a veterinarian.
Definition
Grapes, raisins, and sultanas can cause acute kidney injury (AKI) in dogs. In severe cases, this can progress to oliguric or anuric renal failure, in which very little or no urine is produced.
The kidney-damaging effect of grapes and raisins has been known for a long time. In the meantime, the understanding of their cause has also improved significantly: tartaric acid and certain tartaric acid salts are now considered the likely toxic agents.
A special feature of this poisoning is its low predictability. The tartaric acid content of grapes and their dried products can fluctuate considerably. In addition, individual differences in dogs contribute to variable sensitivity. Therefore, it cannot be reliably derived from the number or weight of the ingested fruits whether renal damage will occur. A generally safe ingestion amount cannot be specified.
For cats, the data situation is significantly lower. While poisoning in dogs is well documented by larger case series, comparable studies for cats are lacking. Ingestion should nevertheless be clarified by a veterinarian as a precaution.
If a dog has ingested grapes, raisins, or sultanas, veterinary advice should be sought promptly – even if no symptoms are present yet. One should not wait to see if vomiting or other signs of illness occur.
The following information is particularly helpful for risk assessment:
- body weight of the animal
- Type of product ingested
- estimated number or quantity
- time of ingestion
- already existing symptoms
- Any other components of the ingested food
An acute emergency exists in particular with:
- significantly reduced or absent urine production
- repeated or persistent vomiting
- pronounced weakness or apathy
- collapse or signs of shock
- Convulsions or impaired consciousness
In cats, too, veterinary advice should be sought early after a known ingestion.
The most important facts at a glance
Grapes, raisins, and sultanas can cause acute kidney injury (AKI) up to life-threatening renal failure in dogs. According to current knowledge, tartaric acid or certain tartaric acid salts are considered the likely toxic principle. Since the tartaric acid content of the fruits fluctuates considerably and individual differences exist between dogs, no generally safe ingestion amount can be established.
Initial symptoms often occur within 6–12 hours. Typical symptoms are vomiting, loss of appetite, lethargy, abdominal pain, and diarrhea. Renal damage can develop within 24–72 hours.
After a known ingestion, one should not wait for symptoms. Early veterinary assessment and, if necessary, decontamination are crucial. If there is a relevant risk, intravenous fluid therapy for at least 48 hours as well as close monitoring of renal function, urine production, and fluid balance may be required. A significantly reduced or absent urine production is a particularly serious warning sign. For cats, the scientific data situation is significantly more limited; in their case, too, ingestion should be clarified by a veterinarian as a precaution.
Causes, development and progression
Poisoning occurs after the ingestion of fruits from the genus Vitis, particularly grapes as well as raisins and sultanas produced from them. Foods containing raisins or sultanas can also be relevant.
Earlier attempts at explanation blamed mycotoxins, pesticides, or various plant ingredients for the kidney damage. These hypotheses no longer correspond to the current state of scientific evidence.
A decisive clue was provided by poisoning cases following the ingestion of cream of tartar and tamarinds. Wegenast and colleagues described six dogs in 2022 that developed acute kidney injury after such ingestion. Clinical, laboratory diagnostic, and histopathological changes corresponded to the already known findings in grape and raisin poisoning. The common link is tartaric acid.
The tartaric acid content in grapes, raisins, and other related products is not constant. This provides a plausible explanation for why the same number of fruits does not necessarily represent the same risk with different exposure.
A generally safe dose therefore cannot be specified. Published amounts at which kidney damage was observed are not threshold values below which ingestion can be considered harmless.
The clinical course may initially be characterized by gastrointestinal symptoms. In affected dogs, acute kidney injury can develop within 24–72 hours.
Mechanism of action
According to current knowledge, tartaric acid is considered the likely decisive toxic principle of grape and raisin poisoning in dogs. The primary target organ is the kidney. In particular, the proximal tubule cells are damaged. In severe cases, acute kidney injury occurs with increasing restriction of renal function, leading to oliguria and anuria.
Experimental studies by Coyne and Landry from 2023 show that tartaric acid damages canine renal cells in a concentration-dependent manner. In this process, organic anion transporters (OAT) are involved in the transport of tartaric acid. The inhibition of OAT-1 reduced tartaric acid-induced cell damage in the cell model. The expression of human OAT-4 in canine renal cells also reduced toxicity.
These results provide an important approach to explaining the particular sensitivity of canine renal cells to tartaric acid. The extent to which differences in these transport mechanisms also determine the varying sensitivity of individual dogs has not yet been fully clarified.
The variable tartaric acid content of the ingested fruits and the individual differences in dogs explain the significant variability of the clinical course. Therefore, a reliable individual dose-response relationship cannot be specified.
Symptoms of intoxication
Initial gastrointestinal symptoms often occur within 6–12 hours, but may also only become apparent later, within the first 24 hours.
Typical early symptoms are:
- Vomiting
- Loss of appetite
- Lethargy
- Diarrhea
- Bauchschmerzen
- Weakness
- increased thirst
- Dehydration
Vomiting is one of the most common early signs of illness.
In the further course, acute kidney injury can develop within 24–72 hours. Urine production may change initially and decrease significantly as renal damage increases.
Particularly alarming are:
- significantly reduced urine production (oliguria)
- complete absence of urine production (anuria)
- persistent Vomiting
- pronounced weakness or apathy
- neurological symptoms in severe uremia
A lack of symptomatology immediately after ingestion does not mean that later renal damage is excluded.
Diagnosis
The diagnosis is primarily based on the medical history, the clinical course, and the repeated assessment of renal function.
The information on whether grapes, raisins, or sultanas were ingested is crucial. The timing and estimated amount should be recorded as accurately as possible. A routinely available specific test for detecting grape or tartaric acid intoxication is not available for clinical diagnostics.
The examination includes in particular:
- clinical examination
- creatinine and urea
- electrolytes and phosphate
- Acid-base status if necessary
- Urinalysis including urine concentration
- Quantitative monitoring of urine production
- repeated monitoring of renal parameters
At the beginning, renal values may still be unremarkable. A single normal blood test immediately after ingestion therefore does not exclude renal damage occurring later.
With corresponding symptomatology, other causes of acute kidney injury must also be considered.
Therapeutic principles
A specific antidote does not exist. Treatment depends on the timing and extent of ingestion as well as the clinical condition and renal function.
Early decontamination
In a clinically unremarkable dog, inducing vomiting may be indicated after recent ingestion. The decision and execution belong in veterinary hands.
Pet owners should not independently induce vomiting.
The efficacy of activated charcoal in grape and raisin intoxications is not sufficiently proven. Therefore, routine repeated administration is not part of standard therapy.
Fluid therapy and monitoring
After relevant ingestion, inpatient intravenous fluid therapy for at least 48 hours may be indicated. It serves to maintain a normal hydration status and sufficient renal perfusion during the critical phase. However, damage to the renal tubules that has already occurred cannot be “flushed out” or reversed by infusions.
During treatment, creatinine, urea, electrolytes, urine production, hydration status, body weight, and fluid balance are monitored in particular. Depending on the severity, blood pressure and acid-base status are also part of the monitoring.
The infusion volume is individually adapted to the patient. As long as there is sufficient urine production, fluid therapy supports hydration and renal perfusion. If urine production drops significantly or anuria develops, the fluid intake must not be increased uncritically. If renal excretion is absent, there is a risk of fluid overload.
Since AKI can develop within 24–72 hours, renal function should be monitored during this risk window. Therefore, fluid therapy is not automatically ended after 48 hours. The further duration depends on renal values, urine production, fluid balance, and the clinical course.
In case of acute kidney injury
If AKI has already developed, treatment depends on its severity and existing complications. This includes carefully adjusted fluid and electrolyte therapy as well as the treatment of nausea, vomiting, and other uremic complaints.
In cases of severe oliguric or anuric renal failure, renal replacement therapy, such as hemodialysis or continuous renal replacement therapy, may be required.
Prognosis & follow-up care
The prognosis depends significantly on whether renal damage is already present and how pronounced it is. Dogs that are presented early and show no evidence of renal damage have a significantly more favorable starting situation.
In a retrospective study of 139 exposed dogs, 8 out of 120 dogs with available laboratory values developed AKI; 138 out of 139 dogs survived. However, since 88% of the animals underwent gastrointestinal decontamination, no untreated disease risk can be derived from this.
The prognosis is significantly less favorable in cases of pronounced oliguria and especially in cases of persistent anuria.
After confirmed acute kidney injury, further monitoring of renal function is required. The scope and duration of follow-up care depend on the individual course.
Research outlook
The central research question has changed in recent years. While research previously searched for an unknown toxin in grapes, research today focuses on tartaric acid and its nephrotoxic mechanism of action.
Of particular interest are the transport of tartaric acid in the renal tubule cells, the causes of individual differences in sensitivity, the variability of the tartaric acid content of different fruits and products, and a better risk assessment after a specific ingestion.
Previous studies already explain essential features of grape and raisin poisoning. However, further studies are required for a reliable individual risk prognosis based on tartaric acid content, ingested amount, and body weight.
Frequently asked questions (FAQs)
1. How many grapes or raisins are dangerous for my dog?
A toxic dose valid for every dog cannot be specified. The tartaric acid content can vary considerably between individual fruits and products. Individual differences also play a role. A known ingestion should therefore not be classified as harmless based on a supposedly safe threshold dose.
2. Why are grapes toxic to dogs?
According to current research, tartaric acid or certain tartaric acid salts are considered the likely toxic principle. They specifically damage the proximal tubule cells of the kidney and can thereby trigger acute kidney injury.
3. Why do some dogs seem to tolerate grapes without problems?
The tartaric acid content varies between fruits. Additionally, there are individual differences between dogs. Therefore, it cannot be concluded from a previous ingestion without consequences that grapes are harmless for this dog.
4. Are raisins more dangerous than fresh grapes?
Raisins are dried grapes and can also cause relevant tartaric acid exposure. Because they are small and easily ingested in large numbers, the amount actually eaten can be underestimated. A safe number of pieces cannot be determined.
5. Are seedless or peeled grapes harmless?
No. The toxicity is not limited to the seeds. Seedless grapes can also cause poisoning.
6. My dog ate grapes but shows no symptoms. Do I still need to react?
Yes. Initial symptoms may only appear hours after ingestion, and renal values may also still be normal at first. After a known ingestion, veterinary advice should therefore be sought early.
7. Can I make my dog vomit at home?
No, this should not be attempted independently. Whether inducing vomiting is sensible and safe depends, among other things, on the timing of ingestion and the condition of the dog and should be decided by a veterinarian.
8. How do I recognize the onset of poisoning?
Vomiting, loss of appetite, lethargy, diarrhea, and abdominal pain often occur first. A significantly reduced or absent urine production indicates severe renal damage and is an acute warning sign.
9. Can cats also be poisoned by grapes or raisins?
For cats, the scientific data situation is significantly lower than for dogs. A comparably well-characterized toxicosis in cats has not yet been documented. After ingestion, veterinary advice should nevertheless be sought as a precaution.
10. Can a dog survive grape or raisin poisoning?
Yes. Particularly with early presentation, before severe renal damage has occurred, the course can be favorable. In the case of oliguric or anuric renal failure, the prognosis is significantly less favorable, and intensive treatment up to dialysis may be required.
Literature
Eubig PA, Brady MS, Gwaltney-Brant SM, Khan SA, Mazzaferro EM, Morrow CM. 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):663–674. doi:10.1111/j.1939-1676.2005.tb02744.x. PMID: 16231710.
Reich CF, Salcedo MC, Koenigshof AM, Hopp MM, Walker JM, Schildt JC, Beal MW. Retrospective evaluation of the clinical course and outcome following grape or raisin ingestion in dogs (2005–2014): 139 cases. Journal of Veterinary Emergency and Critical Care. 2020;30(1):60–65. doi:10.1111/vec.12905. PMID: 31714003.
Croft R, Clementi E, Farmer H, Whalley R, Dunning M, Firth A. Retrospective evaluation of Vitis vinifera ingestion in dogs presented to emergency clinics in the UK (2012–2016): 606 cases. Journal of Veterinary Emergency and Critical Care. 2021;31(1):74–79.
Wegenast CA, Meadows ID, Anderson RE, Southard T, González Barrientos CR, Wismer TA. 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):812–816. doi:10.1111/vec.13234. PMID: 35869755.
Coyne SR, Landry GM. Tartaric acid induces toxicity in Madin-Darby canine kidney cells, but not human kidney-2 cells in vitro, and is prevented by organic anion transporter inhibition and human OAT-4 transfection. Journal of Veterinary Emergency and Critical Care. 2023;33(3):298–304. doi:10.1111/vec.13294. PMID: 37087614.
Hayes C. Grape, Raisin, and Tamarind (Vitis spp, Tamarindus spp) Toxicosis in Dogs. Merck Veterinary Manual, Professional Version. Full review September 2024.