I’m afraid I may have inadvertently done some harm early in my veterinary career. When owners asked me which "human foods" were okay to feed as an occasional canine treat, my reply was typically "a few apple slices, mini-carrots, or grapes would be fine."

Now I omit the grapes, and for good reason. It turns out that they (and their dried cousin, the raisin) can cause acute kidney failure in dogs.

Looking back, I can’t point to any one particular case of kidney failure I treated that I now think was caused by grape ingestion, but since we oftentimes can’t identify the trigger, I’ll never know for sure. In my defense, we just didn’t know that grapes were dangerous 13 years ago when I graduated from veterinary school, and frankly, we still don’t have a good grip on what exactly is going on.

What we do know is this:

• The causative agent, which has not yet been identified, appears to be in the flesh of the fruit. Peeled grapes or seedless varieties don’t appear to be any less toxic.

• Raisins are more dangerous than grapes, probably because they are dried and are therefore hold a more concentrated form of the toxin.

• There is a lot of variation in how individual dogs react to eating grapes. Some can eat relatively large amounts with no adverse effects, while in others very small exposures can lead to big problems.

• Cats also appear susceptible, but since most cats aren’t interested in eating grapes or raisins we don’t see as many problems with them.

Initially, dogs that have eaten grapes or raisins may experience nausea and vomiting, followed by diarrhea, increased thirst and urination, and lethargy. If the kidneys continue to shut down, urine production may slow and eventually stop altogether. Bad breath and oral ulcers develop as uremic toxins build up in the body, and affected dogs can finally lapse into a coma and die.

If you know that your dog has eaten grapes or raisins, call your veterinarian immediately. Inducing vomiting within a few hours of ingestion can remove some of the toxin before it enters the bloodstream. The oral administration of activated charcoal can also help bind the toxin and prevent its absorption.

Treatment for kidney failure centers on diuresis, typically via aggressive intravenous fluid therapy to support kidney function and flush toxins from the body, and symptomatic care (e.g., anti-nausea medications and gastric protectants to prevent or treat stomach ulcers). Mild to moderately affected individuals will usually recover with appropriate care, albeit with permanently reduced kidney function, but if urine production stops, the prognosis becomes poor.

To be on the safe side, never offer your dogs grapes or raisins. Focus on feeding a high-quality food that provides balanced nutrition derived from natural ingredients, and keep all the treats (commercially prepared or out of the kitchen) to less than 10 percent of your dog’s diet … and yes, carrots and apple slices are still okay, at least as far as we know in 2012!

Dr. Jennifer Coates

Image: Artem Kursin / via Shutterstock