Why Are (Some) Grapes Toxic For (Some) Dogs?

    As an emergency veterinary nurse, I saw many dogs presented for toxin exposure. Rat bait, prescription medications, NSAIDs, chocolate ... grapes? While many pet owners are still surprised to find out grapes are toxic, veterinarians have been suspect of the fruit as early as 1998, when an association was noted between otherwise unexplained kidney failure and recent consumption of grapes or raisins. These concerns were popularized in a 2001 JAVMA Letter to the Editor, and several studies followed to try and discern the mechanism underlying this association. Curiously, only some dogs experienced the kidney injury, and not always the first time they ate grapes. It was also never clear what amount of grapes was toxic, as it seemed to vary considerably between case reports. For over two decades, answers eluded researchers, prompting poison control centers to treat any exposure to any amount of grapes as a medical emergency, and leading veterinarians to urge pet owners to never allow their dog to consume grapes. These recommendations haven't changed, but as of March 2021, the cause of toxicosis may have finally been revealed.