A reader recently wrote in to us about a situation in which her dog had consumed some fallen birdseed mix in her backyard.

No big deal? Wrong. The mix contained raisins, which can be toxic to dogs. When the dog got sick, she asked around, and it seemed that very few people knew about the hazard.

We both have been veterinarians for close to 20 years, and while in vet school raisins were not discussed as a potential toxin. It was not until about 10 years ago that they were discovered to cause kidney damage in dogs.

It is unsure if this is a new problem or just newly recognized problem that has been present all along. Itís hard to believe something as innocent as feeding the birds in your yard could result in your dog needing a visit to the emergency room.

What is toxic about raisins has not been identified. Toxicologists suspect it may be a toxin produced by a fungus or mold that grows on the raisins, called a mycotoxin. Interestingly, this toxin does not cause a problem in people.

Grapes are just as toxic as raisins, which makes sense as raisins are just dehydrated grapes. Toxicity has been seen with all varieties.

We are not sure if they are toxic in cats, but there have been several suspicious cases. Fortunately, it is unusual for cats to eat grapes and raisins, so this is a rare issue for them.

It takes about 3-4 raisins per pound of dog (and the same number of grapes/pound) to injure the kidneys. Often the first symptom is vomiting several hours after ingesting the raisins. Seeing them in the vomit is a sure sign they were eaten and should trigger an immediate call to the vet ER. Diarrhea and lethargy follow soon after. Some dogs may have symptoms associated with brain involvement. They may have reduced consciousness, seizures, stumbling gait and tremors.

Around 24-48 hours after ingestion, the toxins that the kidneys filter from the blood begin to elevate. These are the blood urea nitrogen and the creatinine and are produced by normal body metabolism. Normally, the kidneys keep these levels low by removing them from the blood and excreting them into the urine. Elevations in these compounds cause progression of the symptoms and eventual death.

If raisin or grape toxicity is suspected, contact a veterinarian immediately. Vomiting can be induced to eliminate as many from the stomach as possible if done within an hour or two of ingestion. After this time, activated charcoal can be given to inhibit absorption of the toxin from the intestines.

Intravenous fluids should be given for at least 48 hours to promote urination. As long as urine is being produced, there is hope. It is when the kidneys stop producing urine that we usually cannot save them. The kidneys have little capacity to regenerate once damaged. Prevention is key, but early intervention is your next best option.

Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to petdocs@postandcourier.com.