Grape / Raisin Toxicosis

Grape/raisin toxicosis is an acute, potentially fatal intoxication in dogs resulting from the ingestion of grapes (Vitis vinifera) or their dried forms (raisins, sultanas, currants). The condition is characterized by acute kidney injury (AKI) with rapid onset of oliguria or anuria, azotemia, and hypercalcemia. The toxic principle remains unidentified, but it is believed to be a mycotoxin or a metabolite in the fruit that causes renal tubular necrosis. Clinical signs typically develop within 6–24 hours post-ingestion, and without prompt decontamination and aggressive fluid therapy, the condition can progress to irreversible renal failure and death. The disease is recognized worldwide, with a higher incidence in dogs, and is considered a medical emergency requiring immediate veterinary intervention.

The exact toxic agent in grapes and raisins is unknown, but several hypotheses have been proposed. These include: (1) mycotoxins (e.g., ochratoxin, citrinin) produced by fungi (Aspergillus, Penicillium) that contaminate the fruit; (2) high levels of tartaric acid and potassium bitartrate, which may cause renal tubular damage; (3) tannins or polyphenolic compounds that induce oxidative stress; (4) a yet-unidentified nephrotoxin that is concentrated during the drying process (raisins are more toxic per gram). The toxic principle is present in both fresh grapes and dried forms, and toxicity is not dose-dependent in a predictable manner—some dogs develop AKI after ingesting a small number of grapes, while others may ingest large quantities without clinical signs. The toxin is absorbed rapidly from the gastrointestinal tract and directly damages renal tubular epithelial cells, particularly in the proximal tubules. There is no breed, age, or sex predilection, but individual susceptibility varies widely.

Grape/raisin toxicosis is reported predominantly in dogs, with no known breed, age, or sex predilection. However, certain breeds may be overrepresented in some case series, possibly due to dietary habits or genetic susceptibility, but no definitive genetic link has been established. The condition is most commonly seen in dogs that have access to grapes, raisins, or products containing them (e.g., fruit cakes, trail mix, cookies). The incidence is higher during holiday seasons (Thanksgiving, Christmas, Easter) when these foods are more prevalent in households. Cats are rarely affected, likely due to dietary differences, but cases have been reported. The toxic dose is highly variable: some dogs develop AKI after ingesting as little as 0.1–0.3 oz of grapes per kg body weight (approximately 1–2 grapes per kg), while others may ingest larger amounts without clinical signs. This variability complicates risk assessment and necessitates aggressive management in all cases of known or suspected ingestion.

The pathophysiology of grape/raisin toxicosis involves direct nephrotoxicity leading to acute tubular necrosis (ATN). The unidentified toxin is absorbed from the gastrointestinal tract and reaches the kidneys via the systemic circulation. It is filtered by the glomeruli and taken up by proximal tubular epithelial cells, where it causes cellular injury through oxidative stress, mitochondrial dysfunction, and disruption of cellular membranes. This leads to tubular cell death, sloughing of epithelial cells into the tubular lumen, and obstruction of the tubules. The resulting decrease in glomerular filtration rate (GFR) causes azotemia, oliguria, and eventually anuria. Concurrently, there is an increase in serum calcium levels, likely due to release of calcium from damaged cells and decreased renal excretion. Hypercalcemia further exacerbates renal injury by causing vasoconstriction and calcification of renal tissue. The inflammatory response to tubular necrosis leads to interstitial nephritis and fibrosis. If the insult is severe, the kidneys may undergo cortical necrosis, leading to irreversible renal failure. The onset of clinical signs is rapid, often within 6–24 hours, and the severity of renal injury is not always dose-dependent, suggesting individual susceptibility factors.

Predisposing factors for grape/raisin toxicosis include: (1) access to grapes or raisins, especially in households where these foods are commonly consumed; (2) dogs with a tendency to scavenge or ingest non-food items (pica); (3) lack of owner awareness of the toxicity of grapes and raisins; (4) concurrent ingestion of other nephrotoxic substances (e.g., NSAIDs, ethylene glycol) that may potentiate renal injury; (5) pre-existing renal disease or decreased renal reserve, which may increase susceptibility to AKI; (6) young age, as puppies may be more curious and ingest larger quantities relative to body weight; (7) individual genetic variability in metabolism or detoxification of the toxin, which may explain why some dogs are more susceptible than others. However, the most important factor is the ingestion itself, and any dog with known or suspected exposure should be treated aggressively regardless of dose.

Clinical signs of grape/raisin toxicosis typically develop within 6–24 hours after ingestion and may progress rapidly. Early signs are primarily gastrointestinal and include: vomiting (often within 2–6 hours), diarrhea, anorexia, lethargy, and abdominal pain. These signs are followed by signs of acute kidney injury, which may appear within 24–72 hours: polyuria or oliguria (progressing to anuria), polydipsia or decreased thirst, dehydration, weakness, depression, and halitosis (uremic breath). As azotemia worsens, additional signs may include: oral ulceration, uremic gastritis with vomiting, melena, seizures, muscle fasciculations, and coma. Physical examination may reveal pale mucous membranes, prolonged capillary refill time, tachycardia, and palpably enlarged, painful kidneys. In severe cases, cardiac arrhythmias may occur due to hyperkalemia and uremic pericarditis. The clinical course can be peracute (death within 24–48 hours) or subacute (progressive renal failure over several days). Chronic kidney disease may develop in survivors.

Differential diagnoses for grape/raisin toxicosis include: (1) Ethylene glycol toxicity: also causes acute kidney injury with hypercalcemia and oxalate crystalluria; differentiate by history of antifreeze exposure, early CNS signs, and calcium oxalate crystals in urine; (2) NSAID toxicity (e.g., ibuprofen, naproxen): causes gastrointestinal ulceration and renal papillary necrosis; differentiate by history and presence of metabolic acidosis; (3) Leptospirosis: causes acute renal failure with fever, icterus, and thrombocytopenia; differentiate by serology/PCR and exposure history; (4) Acute pyelonephritis: causes fever, flank pain, and bacteriuria; differentiate by urinalysis and culture; (5) Amyloidosis: causes proteinuria and progressive renal failure; differentiate by biopsy; (6) Renal lymphoma: causes renomegaly and renal failure; differentiate by imaging and cytology; (7) Toxic nephropathy from other substances (e.g., lilies in cats, zinc, vitamin D): differentiate by history and specific toxicology testing; (8) Chronic kidney disease with acute decompensation: differentiate by history of pre-existing renal disease and imaging findings. A thorough history of dietary indiscretion is crucial for diagnosis.

The diagnostic algorithm for grape/raisin toxicosis begins with a thorough history, specifically questioning the owner about possible ingestion of grapes, raisins, or products containing them. If ingestion is confirmed or suspected, immediate decontamination (emesis induction if within 2–4 hours) and administration of activated charcoal should be performed. Baseline blood work (CBC, serum biochemistry, electrolytes, blood gas) and urinalysis should be obtained to assess renal function and electrolyte balance. Key diagnostic findings include: elevated BUN and creatinine, hypercalcemia, hyperphosphatemia, hyperkalemia (in oliguric/anuric stages), and isosthenuria (USG < 1.030) with granular casts and renal tubular epithelial cells in the urine. If the patient is oliguric or anuric, a urinary catheter may be placed to monitor urine output. Abdominal ultrasound may show enlarged kidneys with increased cortical echogenicity and loss of corticomedullary distinction. In cases where the diagnosis is uncertain, renal biopsy may be considered, but it is rarely necessary. Serial monitoring of renal parameters (BUN, creatinine, phosphorus, calcium, potassium) and urine output is essential to guide therapy and assess prognosis.

Laboratory findings in grape/raisin toxicosis reflect acute kidney injury and electrolyte disturbances. Complete blood count (CBC) may show hemoconcentration (elevated PCV) due to dehydration, and a stress leukogram. Serum biochemistry typically reveals: marked azotemia (elevated BUN and creatinine), hyperphosphatemia, hypercalcemia (in up to 50% of cases), hyperkalemia (especially in oliguric/anuric stages), and metabolic acidosis (decreased bicarbonate). Liver enzymes may be mildly elevated due to hepatic congestion or hypoxia. Urinalysis is crucial: urine specific gravity (USG) is often isosthenuric (<1.030) or hyposthenuric, and the sediment may contain renal tubular epithelial cells, granular casts, and occasionally red blood cells. Proteinuria may be present. Blood gas analysis confirms metabolic acidosis. Specific biomarkers such as symmetric dimethylarginine (SDMA) may be elevated earlier than creatinine, but its utility in acute toxicity is limited. In cases of suspected mycotoxin involvement, analysis of vomitus or gastric contents for mycotoxins may be attempted, but this is not routinely available. Serial monitoring of renal parameters is essential to track progression or recovery.

Imaging findings in grape/raisin toxicosis are primarily supportive and help rule out other causes of acute renal failure. Abdominal radiography may show renomegaly (enlarged kidneys) and loss of retroperitoneal detail due to effusion. However, radiography is not specific. Abdominal ultrasonography is more useful: affected kidneys may appear enlarged with increased cortical echogenicity, loss of corticomedullary distinction, and perirenal fluid. Doppler ultrasound may show decreased renal blood flow. In chronic cases, kidneys may be small and irregular. Thoracic radiography may reveal pulmonary edema if fluid overload occurs during treatment. Advanced imaging such as CT or MRI is rarely indicated but may be used to assess renal perfusion or detect infarcts. In cases where ethylene glycol toxicity is suspected, ultrasound may show hyperechoic renal cortices due to calcium oxalate deposition, but this is not specific. Imaging is not diagnostic for grape/raisin toxicosis but aids in assessing renal morphology and ruling out obstructive uropathy or other structural lesions.

Cytology and histopathology are not typically performed for antemortem diagnosis of grape/raisin toxicosis, but if renal biopsy is obtained, histopathological findings include: acute tubular necrosis (ATN) with degeneration and sloughing of proximal tubular epithelial cells, tubular casts, interstitial edema, and mild to moderate interstitial nephritis. In severe cases, there may be cortical necrosis and mineralization. Electron microscopy may show mitochondrial swelling and disruption of brush border microvilli. Special stains (e.g., von Kossa) can demonstrate calcium deposition in tubular basement membranes. If the animal dies, postmortem examination may reveal pale, swollen kidneys with cortical necrosis. Histopathology is useful to confirm the diagnosis and rule out other causes of renal failure, but it is not necessary for clinical management. In cases where the toxin is suspected to be a mycotoxin, analysis of renal tissue for mycotoxins may be attempted, but this is rarely available.

Treatment of grape/raisin toxicosis is primarily supportive and aimed at preventing or managing acute kidney injury. The following steps are recommended: (1) Immediate decontamination: If ingestion occurred within 2–4 hours, induce emesis (e.g., apomorphine 0.03 mg/kg IV or 0.04 mg/kg IM in dogs; or hydrogen peroxide 1–2 mL/kg PO, but with caution) and administer activated charcoal (1–2 g/kg PO) to reduce absorption. (2) Aggressive intravenous fluid therapy: Administer isotonic crystalloids (e.g., 0.9% NaCl or lactated Ringer's) at a rate to promote diuresis (e.g., 2–3 times maintenance, typically 60–90 mL/kg/day in dogs, adjusted based on hydration status and urine output). The goal is to maintain urine output at 1–2 mL/kg/hour. (3) Monitor renal parameters and electrolytes closely, adjusting fluid therapy as needed. (4) If oliguria or anuria develops, consider diuretics: furosemide (1–2 mg/kg IV, may be repeated or given as CRI at 0.1–0.5 mg/kg/hour) or mannitol (0.25–0.5 g/kg IV over 20 minutes, if not anuric). (5) Manage hyperkalemia: If severe (>6.0 mmol/L), administer 10% calcium gluconate (0.5–1.0 mL/kg IV over 10–20 minutes) for cardioprotection, and consider insulin/glucose therapy (regular insulin 0.1 U/kg IV with dextrose 2 g/U insulin) or sodium bicarbonate (1–2 mEq/kg IV) for metabolic acidosis. (6) Provide gastrointestinal protectants: Antiemetics (e.g., maropitant 1 mg/kg SC q24h) and H2 blockers (e.g., famotidine 0.5 mg/kg IV/PO q12h) or proton pump inhibitors (e.g., omeprazole 0.7–1.0 mg/kg PO q24h) to manage uremic gastritis. (7) Consider renal replacement therapy (hemodialysis or peritoneal dialysis) in severe cases with refractory oliguria/anuria or life-threatening electrolyte imbalances. (8) Nutritional support: If vomiting is controlled, provide a renal-friendly diet; if not, consider enteral feeding via nasogastric tube. (9) Avoid nephrotoxic drugs (e.g., NSAIDs, aminoglycosides). (10) In cases of severe hypercalcemia, consider treatment with saline diuresis and possibly furosemide or corticosteroids, but these are rarely needed. Prognosis is guarded to poor if anuria develops.

The prognosis for grape/raisin toxicosis is variable and depends on the dose ingested, the time to treatment, and the severity of renal injury. Dogs that receive early decontamination and aggressive fluid therapy before the onset of azotemia generally have a good prognosis. However, once acute kidney injury is established, the prognosis is guarded. Mortality rates in published case series range from 30% to 50%, with higher mortality in dogs that develop oliguria or anuria. Negative prognostic indicators include: severe azotemia (creatinine > 5 mg/dL), hypercalcemia, oliguria/anuria, and lack of response to fluid therapy within 24–48 hours. Dogs that recover may have residual renal damage and may develop chronic kidney disease, requiring long-term management. Serial monitoring of renal parameters is essential to assess recovery. If renal function improves within 72 hours, the prognosis is better. In cases where hemodialysis is available, the prognosis may be improved, but this is not widely accessible.

Follow-up for dogs with grape/raisin toxicosis is critical to monitor renal recovery and manage complications. After initial stabilization, patients should be hospitalized for at least 48–72 hours, with serial monitoring of body weight, urine output, BUN, creatinine, phosphorus, calcium, potassium, and acid-base status every 12–24 hours. Once the patient is stable and eating, they can be discharged with instructions for home monitoring. Recheck appointments should be scheduled at 1 week, 2 weeks, and 1 month post-discharge to assess renal function (BUN, creatinine, SDMA, urinalysis, blood pressure). If azotemia persists, further monitoring at 3-month intervals is recommended. Long-term management may include a renal-friendly diet, phosphate binders (e.g., aluminum hydroxide 30–100 mg/kg/day PO divided with meals), and antihypertensive therapy (e.g., amlodipine 0.1–0.5 mg/kg PO q24h) if hypertension develops. Owners should be educated to prevent future access to grapes and raisins. In cases of chronic kidney disease, IRIS staging and treatment guidelines should be followed.

Clinical Pearls: (1) Always ask about grape/raisin ingestion in any dog presenting with acute vomiting and azotemia, even if the owner does not volunteer the history. (2) The toxic dose is unpredictable; treat all ingestions as potentially life-threatening. (3) Early decontamination (emesis within 2–4 hours) and aggressive IV fluid therapy are the most effective interventions. (4) Hypercalcemia is a common finding and may be a clue to the diagnosis. (5) Monitor urine output closely; a urinary catheter may be necessary to accurately measure urine output. (6) Consider hemodialysis early in cases with severe azotemia or oliguria/anuria. Clinical Pitfalls: (1) Do not delay treatment pending laboratory confirmation; initiate decontamination and fluids immediately. (2) Do not use NSAIDs for pain management, as they are nephrotoxic. (3) Avoid overhydration, which can lead to pulmonary edema; monitor central venous pressure if possible. (4) Do not use mannitol if the patient is anuric, as it can cause volume overload. (5) Do not rely on the absence of clinical signs to rule out toxicity; signs may be delayed. (6) Do not discharge the patient prematurely; renal failure can progress over several days.

Current drug protocols for grape/raisin toxicosis are based on Plumb's Veterinary Drug Handbook and include: (1) Emetics: Apomorphine (0.03 mg/kg IV, or 0.04 mg/kg IM; or 0.1 mg/kg subconjunctivally) for dogs; or hydrogen peroxide (1–2 mL/kg PO, max 45 mL) but with caution. (2) Activated charcoal: 1–2 g/kg PO, with a cathartic (e.g., sorbitol) if not contraindicated. (3) Intravenous fluids: Isotonic crystalloids (0.9% NaCl or LRS) at 60–90 mL/kg/day, adjusted to maintain urine output 1–2 mL/kg/hour. (4) Diuretics: Furosemide (1–2 mg/kg IV; may be repeated or CRI at 0.1–0.5 mg/kg/hour) or mannitol (0.25–0.5 g/kg IV over 20 minutes, only if not anuric). (5) Hyperkalemia management: 10% calcium gluconate (0.5–1.0 mL/kg IV over 10–20 minutes) with ECG monitoring; regular insulin (0.1 U/kg IV) with dextrose (2 g per unit of insulin) IV; sodium bicarbonate (1–2 mEq/kg IV) if acidotic. (6) Antiemetics: Maropitant (1 mg/kg SC q24h) or ondansetron (0.1–0.5 mg/kg IV q8–12h). (7) Gastroprotectants: Famotidine (0.5 mg/kg IV/PO q12h) or omeprazole (0.7–1.0 mg/kg PO q24h). (8) Phosphate binders: Aluminum hydroxide (30–100 mg/kg/day PO divided with meals) if hyperphosphatemia persists. (9) Antihypertensives: Amlodipine (0.1–0.5 mg/kg PO q24h) if hypertension develops. (10) Nutritional support: Renal diet or enteral feeding if anorexic. All dosages should be adjusted based on renal function and clinical response.

Evidence-based literature on grape/raisin toxicosis is limited to case reports, retrospective studies, and expert consensus. A landmark retrospective study by Eubig et al. (2005) reviewed 43 cases of grape/raisin ingestion in dogs and found that 50% developed acute renal failure, with a mortality rate of 30%. The study highlighted the unpredictable dose-response relationship and the need for aggressive treatment. Another study by Sutton et al. (2010) reported that early decontamination and fluid therapy improved outcomes. The ASPCA Animal Poison Control Center has published guidelines recommending that all ingestions of grapes or raisins be treated as potentially toxic, with decontamination and 48–72 hours of IV fluid therapy. There are no randomized controlled trials due to ethical reasons. The exact toxic principle remains unidentified, and research is ongoing. Current recommendations are based on clinical experience and expert opinion, emphasizing the importance of prompt intervention and supportive care. ACVIM consensus statements on acute kidney injury provide general guidelines for management, which are applicable to this toxicosis.