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The ASPCA Animal Poison Control Center studies suggest that the lowest documented toxic grape or raisin dose is 0.32 to 0.65 oz/kg (0.15 to 0.32 oz/lb). This means a 20 pound dog can eat as little as 3.2 ounces and have signs of toxicity.
One raisin for a 11 Pound dog is not going to cause problems with his kidney. Though as with any ingestion you will want to watch out for signs of vomiting, diarrhea or lethargic behavior and if any are presenting have him examined by your vet.