Are these foods REALLY toxic?

By Beth Davidow, DVM DACVECC

There are a number of foods that are now known to be toxic to pets. I tend to wonder each time I hear of a new toxicity, “is that really true?” I often think, “Well, I’ve seen lots of dogs who eat that who haven’t had a problem.” The growing list of toxic foods for pets now includes chocolate, onions, grapes, raisins, and chewing gum containing xylitol (many of the sugar free gums). Although I read these new reports critically, working in emergency, I have now seen all these toxicities first-hand.

Chocolate toxicity has been known to many of us for years. Theobromide, a methylxanthine, is the main toxic component, and causes extremely fast heart rates, tremors, and can lead to seizures. The darker the chocolate, the more theobromide is contained in each ounce and the less the pet has to eat of it to cause problems. White chocolate is actually not toxic at any amount. A 60-pound lab would need to eat 20 ounces of milk chocolate to have moderate to severe signs but only three ounces of dark bakers chocolate. Depending on when the chocolate was ingested, we might recommend inducing vomiting or having us administer activated charcoal. (Activated charcoal binds toxins that are in the stomach or intestinal tract so they can’t be absorbed into the blood stream.) We’ve seen many dogs that presented with agitation and severely elevated heart rates. Most have done well but some needed 24-48 hours in the hospital on IV fluids and medication to decrease the dangerously high heart rates.

Onion toxicity is one I hadn’t seen until a few years ago. Onions and other members of the Allium family (shallots, garlic, and green onions) contain a compound that can weaken red blood cells. The red blood cells break down causing anemia (lack of red blood cells) and hemoglobin (the protein inside red blood cells) to spill into the urine. Dog’s red blood cells have less antioxidants than people’s making their cells more prone to damage. Cats are even more susceptible to red blood cell damage. Ingestion of 5g/kg of onion in cats or 15-30 g/kg in dogs can lead to clinically important hemolysis. Damage consistently happens in dogs who ingest more than 0.5% of their body weight in onions at one time. A few years ago, an English setter was referred to us for inappropriate urination and red colored urine. It turns out he had eaten three cups of onions the day before – 1.5% of his body weight! The red color was hemoglobin in his urine. He became very anemic four days after he ate the onions and needed a transfusion. To complicate matters in his case, he also had a bacterial urinary infection. The combination of the hemoglobin going through his kidneys and the infection, despite antibiotics and IV fluids, led to acute kidney shut down. After 10 days of hospitalization, antibiotics, and IV fluids, he is doing well at home.

Grape and raisin toxicity was first reported by the National Animal Poison Center in 2001. At that time, they knew of 10 reported cases of acute kidney failure with ingestion of quantities varying from 0.2 oz/lb to 4.4 oz/lb. A retrospective study was published in 2005 in the Journal of Veterinary Internal Medicine involving 43 cases. Of the 43 cases, 20 died or were euthanized due to a poor prognosis. Unfortunately, it is still not known why some dogs, but not all dogs, develop acute kidney failure from ingestion of these foods. Pesticides, fungus and heavy metal contamination have been ruled out as causes and it appears that the toxic principle is in the flesh and not in the seed. Last year, we treated a dog who developed acute kidney shutdown after eating grapes off a vine at a friend’s house. The dog survived and is now doing well but was hospitalized for almost two weeks and required subcutaneous fluids for many weeks afterward. We do recommend inducing vomiting, activated charcoal and IV fluid diuresis with any grape ingestion over 0.7 oz/kg or raisin ingestions over 0.1oz/kg. Induction of vomiting is recommended up to eight hours after ingestion in these cases as in many of the cases reported to National Animal Poison Center, raisins were still found in the vomit at this point.

Xylitol is a sugar substitute that is good for people on a low carbohydrate diet, those with diabetes or those watching calories. It is found in sugar free gum, some toothpastes (it can prevent oral bacteria from producing acids that damage tooth surfaces), and can be bought as a powder for cooking. Although the lethal dose is >130 g/day in people and greater than 20g/kg in mice, the metabolism is different in dogs. It appears that doses greater than 0.1g/kg can lead to hypoglycemia 30 minutes to 12 hours after ingestion. This is because in dogs, but not in people, xylitol causes a dose-related rapid, severe insulin release. In addition, acute liver failure and bleeding problems has been reported in eight dogs after eating xylitol containing products. Most of the dogs presented with vomiting and lethargy nine to 72 hours after xylitol exposure. The reason for the liver failure is currently unknown. National Animal Poison Center does recommend vomiting induction, IV fluids, and careful monitoring of blood glucose and liver enzymes.

The NAPCC is a fantastic resource and we recommend that their phone number be easily accessible in your household. The Washington Poison Center now also has a veterinary toxicologist on staff and is also very helpful especially in cases of household chemicals or product exposure. In addition, our emergency doctors are very knowledgeable about toxicities and are always happy to answer questions at any time of day or night. (NAPCC, 888-426-4435 and Washington Poison Center, 800-222-1222)