Grapes and raisins are extremely toxic to dogs, so much so that even small amounts can be lethal. It is not known exactly why grapes and raisins are so toxic to dogs, but any amount can trigger acute reactions that require immediate treatment.
Symptoms of grape or raisin poisoning in dogs include vomiting, diarrhea, loss of appetite, lethargy, dehydration and a myriad of kidney-related problems that can result in renal failure. Inducement of vomiting is necessary if it is certain that the dog has ingested any amount of grapes or raisins. Vomiting can be induced through a ratio of 1 teaspoon of hydrogen peroxide per 5 pounds in body weight of the dog. No more than 3 teaspoons of the solution should be given at once. This process can be completed no more than three separate times, each with a 10-minute interval.