It is unclear what substance within these fruits is toxic to dogs. There are several theories: mycotoxin, salicylate, or tartaric acid (including tartrates like potassium bitartrate), are all naturally found in grapes and decrease blood flow to the kidneys.
VCA Hospitals: Acetaminophen Poisoning Alert for Dogs and Cats.
Acetaminophen Intoxication: A Critical-Care Emergency. This toxicity is the most common cause of acute liver failure and the second most common cause of liver failure requiring transplantation. Manouchehr Saljoughian, PharmD, PhD. Author accreditations.

Potential Consequences of Toxicity. Acetaminophen toxicity in dogs can cause severe health problems, including: Liver Damage: One of the most significant risks is severe liver damage, potentially leading to liver failure.
Restricted diet. Underlying liver or kidney disease. Compromised nutritional status (eg, from prolonged fasting, eating disorders, cystic fibrosis, gastroenteritis, chronic alcoholism, or HIV disease).encoded search term (Acetaminophen Toxicity) and Acetaminophen Toxicity.

Generally speaking, a dog can experience acetaminophen toxicity if they take as little as 75 mg per kg of their body weight. This means a smaller dog under 6 kg could experience serious symptoms if they take a 500 mg Tylenol.
Acetaminophen toxicity. Contents. 1 Background.Stage 3 (72-96h): Peak hepatotoxicity markedly elevated AST/ALT (can exceed 10,000), coagulopathy, jaundice, acute kidney injury, hepatic encephalopathy.