Grapes, Sultanas, and Raisins
Poisoning by grapes, sultanas, and raisins represents a serious toxicological problem for pets, especially for dogs and, in rarer cases, for cats. This form of intoxication is an acute poisoning caused by the consumption of fruits of the grapevine (Vitis vinifera) or their dried products. The toxicity of these fruits for dogs was first scientifically documented in 1999, although the exact toxic substance has not yet been fully identified. The individual sensitivity of animals is remarkable – while some dogs develop severe symptoms after consuming only a few grapes or raisins, others show no obvious signs of poisoning even after consuming larger quantities. This variability complicates risk assessment and makes preventive measures all the more important. Regardless of the grape variety (red, green, seedless) or processing form (fresh, dried, in baked goods), there is a risk of poisoning, which is why these foods are generally classified as highly toxic for dogs and cats.
The most important facts at a glance
Poisoning by grapes, raisins, and sultanas poses a serious threat to the health of dogs and, in rarer cases, cats. Despite intensive research, the exact toxic substance has not yet been identified. The toxicity is independent of the grape variety or processing form and can lead to severe poisoning symptoms even in small amounts. Individual sensitivity varies considerably, which complicates risk assessment. The poisoning primarily manifests as acute nephrotoxicity, which can lead to life-threatening kidney failure within a few days. Characteristic symptoms include gastrointestinal complaints such as vomiting and diarrhea, followed by signs of kidney dysfunction such as oliguria to anuria. Diagnosis is based on anamnesis, clinical picture, and laboratory diagnostic findings indicative of kidney damage. Therapy must be initiated immediately and includes decontamination, aggressive fluid therapy, and symptomatic treatment. The prognosis is favorable with early intervention but drastically worsens with manifest kidney failure. Aftercare requires long-term monitoring of kidney function. Prevention through strict avoidance of access to grapes and grape products remains the most important measure for protecting pets.
Causes, development and progression
Grapes and their dried products can lead to poisoning symptoms in dogs even when relatively small amounts are consumed.
Not all dogs are equally sensitive.
Cats tend not to eat grapes, so they are not as much at risk.
The exact mechanism of action of grape poisoning has not yet been fully elucidated despite intensive research efforts. Substance-induced nephrotoxicity, which can lead to acute kidney failure, is identified as the main cause of intoxication. Scientific studies suggest that tannins, flavonoids, or certain mycotoxins might be responsible for the toxic effect. Recent studies have also considered tartaric acid as a potential trigger. The toxicity appears to be independent of the cultivation method, country of origin, or processing of the grapes. Even small amounts can lead to severe poisoning symptoms in sensitive animals. A critical dose is considered to be approximately 10–12 g of grapes or 2.8 g of raisins per kilogram of the animal’s body weight, although in individual cases, significantly smaller amounts can also lead to poisoning symptoms. Individual sensitivity varies considerably, which complicates the prediction of poisoning risk. Cats generally seem to be less at risk as they less frequently ingest grapes and dried fruits voluntarily; however, similar toxic effects are to be expected in them if ingested.
Mechanism of action
Kidney insufficiency or kidney failure is considered the cause of intoxications by grapes or their dried products.
However, how the kidneys are damaged in detail is not known.
In some animals, however, even 10–12 g/kg body weight of ingested grapes or 2.8 g of raisins/kg body weight can lead to poisoning symptoms. Kidney failure can occur within 3 days.
Mechanism of Action of Poisoning by Grapes, Raisins, and Sultanas in Dogs and Cats
Poisoning by grapes, raisins, and sultanas is among the most significant food-borne intoxications with potentially fatal outcomes in dogs. For cats, the data is significantly scarcer, and poisoning cases are rarely documented – presumably due to lower acceptance of these foodstuffs. The toxic principle has not yet been conclusively clarified, but it is certain that even small amounts can lead to acute kidney failure, especially in dogs.
1. Affected Substances and Routes of Ingestion
- Grapes (Vitis vinifera) – fresh, cooked, dried (e.g., in cake)
- Raisins and Sultanas – dried grapes
- Juice, baked goods, muesli bars – often contain hidden toxic amounts
Routes of Ingestion:
- Direct oral ingestion (e.g., from the kitchen, table, trash)
- Indirectly via prepared foods; pet owners often unknowingly give them as “healthy treats.”
2. Current Findings on the Toxic Mechanism of Action
Previously Unidentified Active Substance
- Despite intensive toxicological research, the exact active substance has not yet been clearly identified
- Hypotheses include:
- Phenolic compounds or tannins
- Mycotoxins on the fruits
- Oxalic acid derivatives
- Interactions with gut flora or metabolism
Damage to the Proximal Tubules of the Kidney
- In sensitive dogs, direct tubular damage to the kidneys occurs, especially to the proximal tubules.
- This likely occurs through:
- oxidative stress
- Disruption of mitochondrial functions
- Calcium homeostasis disorders
- The result is a sudden onset, often irreversible acute renal failure (ARF)
Hypercalcemia as a Possible Consequence
- In some cases, an increased calcium concentration in the blood
- Possible cause: tubular reabsorption disorder or damage to calcium metabolism
- Hypercalcemia itself may additionally contribute to tubular damage
3. Species Differences
Dog: Highly Sensitive
- Dogs show individually very variable reactions
- In some animals, even a few raisins (5–10 pieces) are enough to cause life-threatening symptoms
- No clear correlation between dose and severity – idiosyncratic reaction is suspected
Cat: Rarely Documented Cases
- Cats rarely ingest grapes and raisins voluntarily
- Case reports exist, but no systematic poisoning data
- Toxicity is not fundamentally excluded, but apparently significantly lower
4. Pathophysiological Changes
| Target Structure | Mechanism of Damage | Consequence |
| Renal Tubules (proximal) | Cell damage due to oxidative stress and mitochondrial dysfunction | Acute Kidney Failure (Anuria, Azotemia) |
| Tubular Reabsorption | Calcium retention or release | Hypercalcemia, secondary toxicity |
| GI Mucosa | Nonspecific irritation or inflammation | Vomiting, diarrhea, abdominal pain |
5. Clinical Symptoms
Symptoms usually begin within 6–24 hours after ingestion, but can also appear delayed:
Early Phase (0–24 H):
- Vomiting (often multiple times)
- Hypersalivation
- Apathy, inappetence
- Abdominal pain
- Diarrhea
Late Phase (24–72 H):
- Azotemia (↑ urea, creatinine)
- Oliguria to Anuria
- Dehydration
- Electrolyte disturbances
- Lethargy, tremors, possibly seizures
- Uremic coma
6. Summary of the Toxic Mechanism of Action
| Toxic Principle | Consequences in Dogs |
| Previously unidentified nephrotoxic substance | Direct damage to the proximal tubules |
| Oxidative stress, mitochondrial damage | Cell death, tubular necrosis |
| Hypercalcemia | Exacerbation of kidney damage, cardiac arrhythmias |
| Idiosyncratic Reaction | No reliable dose-response relationship |
Conclusion
Poisoning by grapes, raisins, and sultanas represents an acute, potentially fatal kidney failure in dogs that can occur even with small amounts. The exact active substance is still unknown, but the toxic processes lead to irreversible tubular kidney damage. Cats are less frequently affected but could also react sensitively. From a veterinary perspective: Even small amounts are considered dangerous, and any suspicion of ingestion requires immediate veterinary intervention.
Symptoms of intoxication
Symptoms usually appear 6–12 hours after raisin ingestion.
- Vomiting
- Bauchschmerzen
- Weakness
- Anorexia
- Diarrhea
- Dehydration
- increased thirst
- Lethargy
- painful abdomen
- Tremor
Laboratory blood findings indicate progressive kidney failure.
In complete kidney failure, almost no urine is produced.
In most cases, euthanasia of the animals then follows.
Clinical signs of poisoning by grapes or their dried products typically develop within 6–12 hours after ingestion. The first symptoms are often non-specific and include gastrointestinal complaints such as repeated vomiting, which can often contain parts of the ingested grapes or raisins. Abdominal pain manifests as a tense abdominal wall and pain reactions upon palpation of the abdomen. Affected animals also show lethargy, weakness, and anorexia. With progressive poisoning, signs of dehydration and incipient kidney failure develop. These include increased thirst (polydipsia) with simultaneously reduced or completely ceased urine production (oliguria to anuria). In severe cases, tremors, ataxia, and neurological deficits can occur. The symptomatology reflects the progressive course of kidney damage, which can lead to complete kidney failure within 24–72 hours after ingestion of the toxic substances. In cats, the symptomatology is similar, although fewer clinical cases are documented due to less frequent ingestion. The severity of symptoms does not always correlate with the ingested amount, which underscores the particular danger of this poisoning.
Diagnosis
The diagnosis of grape or raisin poisoning is primarily based on anamnesis and clinical presentation. Crucial is the detection or reasonable suspicion of ingestion of grapes, raisins, or sultanas, ideally with an estimation of the consumed quantity. Laboratory diagnostic examination includes a complete blood count, serum biochemistry with a special focus on kidney parameters, and urinalysis. Characteristic changes in the blood count are elevated urea (BUN) and creatinine levels as indicators of impaired kidney function. Electrolyte determination can reveal disturbances in potassium, phosphate, and calcium balance. In urinalysis, decreased urine concentration (isosthenuria), proteinuria, glucosuria, and the presence of casts can serve as indicators of tubular kidney damage. Imaging procedures such as ultrasound may show enlarged, edematous kidneys with increased echogenicity of the renal parenchyma. In unclear cases, a kidney biopsy can detect histopathological changes such as acute tubular necrosis. Since no specific toxin detection exists for grape poisoning, the diagnosis often remains a presumptive diagnosis based on the combination of anamnesis, clinical picture, and laboratory diagnostic findings.
Therapeutic principles
There is no antidote.
Regardless of the (presumed) amount of ingested grapes and grape products, immediate and consistent decontamination using emetics (medications to induce vomiting) and repeated administration of activated charcoal is recommended for dogs due to their very varied sensitivity and the very high toxicity for some animals.
As symptomatic therapy, intensive intravenous fluid therapy is administered for 2 to 3 days. Kidney function should be monitored repeatedly at intervals.
If urine production decreases, an attempt should be made to increase renal blood flow using dopamine infusions.
The treatment of poisoning by grapes or dried fruits requires a rapid and consistent therapeutic approach. Decontamination is paramount, provided ingestion occurred less than 4–6 hours ago. For this purpose, vomiting is induced under veterinary supervision, typically by administering apomorphine in dogs or xylazine in cats. This is followed by repeated administration of activated charcoal (1–4 g/kg body weight every 4–6 hours for 24 hours) to reduce the absorption of remaining toxins in the gastrointestinal tract. Fluid therapy forms the backbone of treatment and should be initiated immediately. Aggressive intravenous fluid therapy with crystalloid solutions (60–90 ml/kg/day) serves to maintain renal perfusion and promote diuresis. Fluid administration is continuously adjusted based on hydration status, urine production, and renal parameters. In cases of oliguria or anuria, diuretics such as furosemide or mannitol can be used to stimulate urine production. In severe cases, a low-dose dopamine infusion (1–3 μg/kg/min) can help improve renal blood flow. Symptomatic therapy includes antiemetics such as maropitant or ondansetron for vomiting, gastroprotectants such as omeprazole for gastric irritation, and analgesics for pain. In advanced kidney failure, hemodialysis or peritoneal dialysis can be life-saving, but is not universally available. Monitoring kidney function through regular checks of urea, creatinine, electrolytes, and urine production is essential for therapy management.
Prognosis & follow-up care
The prognosis for poisoning by grapes or dried fruits largely depends on the timing of therapy initiation, the amount ingested, and the individual sensitivity of the animal. With early intervention within the first 4–6 hours after ingestion and successful decontamination, the prognosis is generally good. Animals that have already developed signs of acute kidney failure have a significantly poorer prognosis. Studies show that the mortality rate for manifested kidney failure, despite intensive therapy, can be 50–75%. Aftercare includes regular monitoring of kidney function over several weeks to months. Initially, renal parameters should be checked every 24-48 hours; later, intervals can be extended with positive development. A kidney-supportive diet with reduced protein and phosphorus content can be helpful during the recovery phase. Animals that have survived grape poisoning should be regularly monitored for signs of chronic kidney insufficiency throughout their lives, as subclinical kidney damage may persist even after clinical recovery. Owners must be thoroughly informed about the necessity of strictly avoiding re-exposure, as previous poisonings can increase the risk of more severe consequences upon re-ingestion.
Research outlook
Research on grape toxicity in pets currently focuses on several promising areas. A main focus is on identifying the specific toxic compound in grapes and raisins. Recent studies are investigating various hypotheses, including the possible role of tartaric acid, certain flavonoids, or mycotoxins as triggers of nephrotoxicity. Another research focus concerns genetic factors that could explain the differing sensitivity of various animals. Scientists are working on developing genetic screening methods to identify particularly at-risk animals. In parallel, innovative therapeutic approaches are being explored, including specific antidotes or adsorbents that could neutralize toxic substances more targeted than conventional activated charcoal. Advances in renal replacement therapy, such as portable dialysis machines for veterinary use, could improve treatment options for severe kidney failure. Epidemiological studies also investigate possible correlations between cultivation regions, pesticide use, and grape toxicity. Through international research collaborations and the use of modern analytical methods such as mass spectrometry and metabolomics, it is hoped that the toxic mechanism can be fully elucidated in the near future, thereby enabling the development of more targeted prevention and treatment strategies.
Frequently asked questions (FAQs)
- How many grapes or raisins are dangerous for my dog?
The toxic dose varies greatly among individual animals. As a guideline, approximately 10–12 g of grapes or 2.8 g of raisins per kilogram of body weight are considered. However, in some dogs, significantly smaller amounts can lead to poisoning symptoms. Therefore: Any ingestion of grapes or raisins should be considered potentially dangerous. - Are certain dog breeds more susceptible to grape poisoning?
So far, no clear breed predisposition has been demonstrated. Individual sensitivity does not appear to be breed-specific, but varies from animal to animal, regardless of breed. However, smaller dogs may be at risk from smaller absolute amounts due to their lower body weight. - Are cats as much at risk as dogs?
Cats generally appear to react similarly sensitively to the toxic substances, but due to their selective eating habits, they less frequently ingest grapes or raisins. Therefore, poisoning cases in cats are significantly less documented, but should be treated with the same seriousness. - Are grape seeds or skins particularly toxic?
According to current knowledge, all components of the grape are potentially toxic. There is no evidence that seedless or peeled grapes would be less dangerous. Grape juice and raisins processed in baked goods also pose a risk. - How quickly do I need to act if my pet has eaten grapes?
Immediate action is crucial. Contact your veterinarian or a veterinary emergency clinic immediately, ideally within the first 1–2 hours after ingestion. The sooner decontamination occurs, the better the chances of preventing severe kidney damage. - Can I induce vomiting at home if my pet has eaten grapes?
Self-medication is generally not recommended. Inducing vomiting should only be done under veterinary guidance, as improper execution can lead to complications such as aspiration pneumonia. Instead, go to the veterinarian immediately. - How is grape poisoning diagnosed?
Diagnosis is based on anamnesis (evidence of grape ingestion), clinical symptoms, and laboratory tests, especially kidney values. Since no specific toxin detection exists, the combination of these factors is crucial for diagnosis. - Can my pet survive grape poisoning?
With early and intensive treatment, the prognosis is good. However, if acute kidney failure has already occurred, the chances of survival decrease significantly. The prognosis largely depends on the timing of treatment initiation and the individual animal’s response. - Are there long-term consequences after surviving grape poisoning?
Animals that survive grape poisoning can suffer permanent kidney damage, which may lead to chronic kidney failure. Regular monitoring of kidney function is therefore important even after apparent recovery. - What other foods are similarly dangerous for dogs and cats as grapes?
Besides grapes and raisins, there are other foods toxic to pets, including chocolate, macadamia nuts, onions, garlic, avocados, xylitol (in sugar-free products), and alcohol. Each of these substances can cause severe poisoning symptoms.
Literature
- Eubig, P. A., Brady, M. S., Gwaltney‐Brant, S. M., Khan, S. A., Mazzaferro, E. M., & Morrow, C. M. (2005). 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, 19(5), 663-674.
- https://www.msdvetmanual.com/toxicology/food-hazards/raisins-and-grapes
- Sutton, N. M., & Bates, N. (2021). Canine toxic ingestions: A review of the most common substances reported to the Veterinary Poisons Information Service. The Veterinary Journal, 272, 105658.
- Piripi, F., Carmichael, N., Bates, N., & Dhanani, J. (2019). Grape and raisin toxicity in dogs: A retrospective case series from the Veterinary Poisons Information Service. Journal of Small Animal Practice, 60(10), 598-605.
- Cordeiro, M., Drobatz, K. J., & Giger, U. (2020). Current understanding of grape and raisin toxicosis in dogs: A review. Journal of Veterinary Emergency and Critical Care, 30(2), 132-143.
- Koenigshof, A. M., & Beal, M. W. (2022). Acute kidney injury in dogs and cats: Pathophysiology, diagnosis, and treatment strategies. Veterinary Clinics of North America: Small Animal Practice, 52(3), 669-689.
- Schweighauser, A., & Francey, T. (2020). Extracorporeal blood purification techniques in small animals: Current status and future perspectives. Frontiers in Veterinary Science, 7, 587336.
- Löwe G, Löwe O. Notfälle bei Hund und Katze – Ein tierärztlicher Ratgeber. 2. Auflage. Kreuztal: Kynos-Verlag. 2021; 208 S.