Xylitol is a naturally occurring substance that is widely used a a sugar substitute. Over recent years, the number of products that contain xylitol has greatly increased. It can be found in sugar free gum, candies, breath mints, cough syrup, chewable or gummy vitamins, toothpastes, etc. Also it is frequently found in sugar free foods including baked foods and even peanut butter.
Xylitol is increasing in popularity because it is as sweet as sucrose but contains only about 2/3 of the calories. It is lower on the glycemic index so is great for diabetics or people on low carb diets.
Although xylitol is safe for use in people, it is extremely toxic to dogs. Even small amounts can cause severe hypoglycemia (low blood sugar), seizures, liver failure and death. Xylitol does not stimulate the release of insulin in people, but it does so in dogs. The rapid release of insulin causes rapid and severe decrease in blood sugar levels. This occurs within 10-60 minutes of eating the xylitol. Untreated, this hypoglycemia can be life threatening.
The dose of xylitol that can cause hypoglycemia in dogs is reported as about 50 mg of xylitol/lb of body weight. The higher the dose, the more the risk of liver failure. According o the Pet Poison Helpline the most common xylitol poisonings come from ingesting sugar free gum. Different brands have differing amounts of xylitol/piece of gum. Some have a fairly small amount while others have 1 gm/piece of gum. In the cases of ingestion of the 1 gm/piece of gum it would only take 2 pieces to result in severe hypoglycemia and 10 pieces to result in lover failure in a 40 lb dog.
If your dog eats something containing xylitol please contact your veterinarian or the Pet Poison Helpline ( 1-800-213-6680) immediately.
Do not induce vomiting unless specifically directed to do so by your veterinarian. It is important to get treatment as soon as possible. Inducing vomiting can make them worse if they are already hypoglycemic.
Symptoms of xylitol poisoning develop rapidly (often within 15-30 minutes)
vomiting
weakness
lack of coordination
difficulty walking or standing
depression/lethargy
tremors
seizures
coma

There is no antidote for xylitol toxicity but treatment with sugar supplementation, intravenous fluids, and liver protective drugs is beneficial. The prognosis is good for dogs that are treated before clinical signs develop. If liver failure or bleeding develops the prognosis is poor. If a dog is already in a coma the prognosis is very poor.