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Toxic products

Chocolate, artificial sweetener, onions, raisins and human medications can all be dangerous for your pets. Photo: Myrna MacDonald

What’s in your home that’s hazardous to your pet’s health? Three specialists at the Western College of Veterinary Medicine — Drs. Mark Wickstrom, Jennifer Ogeer and Dennilyn Parker — talk about what makes some common foods and products harmful to your pets, the common clinical signs to watch for, and the therapies that veterinarians use to counteract the toxic effects of these products.

Antifreeze (ethylene glycol)

The sweet taste of antifreeze makes it attractive to most animals, and a spill on the garage floor from a car’s leaking radiator may go unnoticed until it’s too late. The minimum lethal dose of ethylene glycol is one to two millilitres per kilogram. In other words, about two teaspoons of antifreeze can cause death in an average-sized cat, and even the less toxic, diluted antifreeze is still very dangerous.

In antifreeze poisoning cases, treatment must be instituted quickly if it’s to be effective. A sweet odour to a pet’s breath is often the first symptom, and the animal might act drunk or unco-ordinated. Within a few hours, your pet may be depressed, drooling, trembling and unable to stand. The longer treatment is delayed, the less hopeful is the prognosis.

The toxic substance is not the antifreeze itself but a metabolite formed that is directly toxic to the tubules in the kidneys — leading to acute kidney failure. The goal of treatment is to prevent the metabolism of the antifreeze and formation of these crystals in the tubules of the kidneys. This is accomplished by administering fomepizole (4-mehylpyrazole) or intravenous ethanol for several days.


Chocolate is no more than a guilty (and fattening) indulgence for most of us, but it’s poisonous to dogs that metabolize it differently to humans after ingestion. An ounce of milk chocolate per pound of dog is potentially lethal, while dark chocolate is twice as powerful. The most deadly type is unsweetened baker’s chocolate that is 10 times more potent than the chocolate used in a regular candy bar.

The primary toxic agent in chocolate is theobromine, a cardiovascular and central nervous system stimulant. In the initial six hours after ingestion, the first signs of acute toxicity in a pet are vomiting, diarrhea, restlessness, excessive drinking and urinating. Over the next couple of days, clinical signs escalate to include increased hyper-excitability, muscle tremors and seizures, elevated body temperature, increased heart rate and an abnormal heart rhythm. Death results from cardiac and respiratory failure. Lower doses of chocolate sometimes induce gastrointestinal upset or pancreatitis consistent with a dog eating a very high fat meal.

Pets manifesting clinical signs from chocolate toxicity require hospitalization, treatment and monitoring for at least a couple of days because the half-life of theobromine in the body is approximately 15 to 20 hours. A useful first step in treatment is to induce vomiting, but veterinarians may also give repeated doses of activated charcoal. Theobromine is metabolized in the liver and recirculated into the body if activated charcoal isn’t administered to prevent absorption in the gut.

cookieGrapes and raisins

Grapes and raisins seem more unlikely than chocolate to be poisonous to pets, but it has now been documented that some dogs are highly susceptible to the toxic agent they contain. The exact mechanism of action for the toxicity has yet to be clarified, but an ochratoxin found in grapes has been suggested as one possibility.

The toxic effect varies considerably. On average, a half-pound of grapes is dangerous for a medium-sized dog, but death can occur with ingestion of a much similar quantity. Acute kidney failure occurs and can be fatal depending on the quantity of grapes or raisins ingested and the delay to the time of initiating treatment.

Immediate treatment can improve the chances of survival, so it’s important to recognize the clinical signs of poisoning. These signs include vomiting and diarrhea, loss of appetite, depression and abdominal pain. Damage to the tubules in the kidneys can lead to signs of acute kidney failure with decreased to no urine output occurring.

The first step in treatment is to induce vomiting, and the veterinarian will often further decontaminate the stomach with gastric lavage and administer an absorbent such as activated charcoal, followed by two to three days of fluid therapy to diurese the dog’s kidneys.


Xylitol is a popular artificial sweetener found in sugarless gums as well as baked goods, beverages, toothpaste and cereals. While it’s harmless to humans, the artificial sweetener produces a massive release of insulin in dogs. Insulin release leads to a dramatic lowering of the animal’s blood sugar levels within a half-hour to an hour after ingesting xylitol. Clinical signs include vomiting, weakness, depression, inco-ordination and even seizures. Ingestion of quantities of xylitol greater than 0.1 grams per kilogram can induce hypoglycemic symptoms.  Doses of 0.5 gm/kg and higher may cause serious liver damage and subsequently lead to liver failure.

No data is available for cats or other small pets. Given the average dog’s sweet tooth, it’s not surprising that they are prime candidates for xylitol poisoning, and dogs have died after eating as few as half a dozen cookies or several sticks of gum. Treatment involves administration of intravenous glucose or dextrose and monitoring blood glucose regularly. In these cases, veterinarians don’t advise owners to induce vomiting after the symptoms of xylitol toxicity appear.

Over-the-counter and prescription medications

Common medications, especially painkillers such as acetylsalicylic acid (ASA or Aspirin®), acetaminophen (Tylenol®) and ibuprofen can cause serious problems for our pets. However, cases of toxic overdose of these drugs aren’t usually due to accidental ingestion: problems often occur when owners administer these drugs inadvertently to treat ailments such as arthritis in their pets.

Dogs metabolize all three of these common painkillers much more slowly than humans, and toxic doses of acetaminophen and ibuprofen for dogs are very close to therapeutic doses for humans. Cats are much more susceptible than dogs to the toxic effects of all three drugs.

The clinical signs can be manifested as difficulty breathing in cats to lethargy, vomiting and depression in dogs. The initial course of action is to induce vomiting within two to six hours of ingestion of the drugs. However, if a longer period of time has elapsed, the pet must be seen by a veterinarian to have proper therapy instituted immediately.

Houseplants and garden plants

Plant toxicities are challenging to treat as it’s often unknown what plant has been ingested. Veterinarians often begin symptomatic treatment without knowing the exact toxic agent involved. Concentrations of the toxic agents found in plants are widely variable, and it depends on the growing season, the parts of the plant ingested (including whether the leaves are young or old), the plant variety and its habitat.

An increasing number of homeowners are decorating their houses and gardens with an increasing number of exotic plants from around the world. While these plants may be beautiful, some of them are extremely toxic to pets and little information may be known about some of them.

Many plants such as poinsettias are simply local irritants. If they’re ingested by pets, they can cause abdominal pain, vomiting or diarrhea and no further serious side effects. Other plants can be more dangerous. For example, lilies are extremely toxic to cats. Even when small amounts of the leaves and flowers are ingested, life-threatening acute renal failure will occur in cats. Another potential danger is the avocado plant that can be highly toxic to birds, rabbits and to other pocket pets.

onionOnions and garlic

Onions, garlic and chives can be dangerous to your pets — especially cats. Toxic amounts are estimated at about five grams of dehydrated onions per kilogram, and even an ounce of cooked onion can be potentially poisonous to your cat. Dogs are five to six times less sensitive to the toxic effects of onions, garlic and chives.

The toxic agent in onions and garlic is an N-propyl disulphide. It’s believed to cause damage to the red blood cells and denature haemoglobin so oxygen is carried less efficiently in the body. As a result of the fragility of the red blood cells, anemia occurs. A complicating factor is that there’s a long lag time before pets demonstrate the clinical signs of toxicity. These signs include inappetence, abdominal pain, depression, red urine, elevated heart rate and rapid breathing. Treatment includes administration of oxygen and blood transfusions.

Toxic products for pet birds

These days, pet birds are often allowed to fly free in the home instead of spending all of their time in cages. That practice, coupled with birds’ curious natures and their propensity to pick at things with their beaks, puts them at an increased risk of poisoning. For example, a hanging plant that’s toxic for pets can be out of your dog’s reach — but serves as a handy perch for your bird.

That being said, birds are most often poisoned when they eat old birdseed that may contain toxic moulds. They can also be victims of lead toxicity: paint containing lead, the lead used in stained glass, and curtain and ceiling fan weights are the most common sources of lead poisonings. Another potential danger for birds originates from Teflon® coated cooking ware. When these pots and pans are overheated, the Teflon® coating emits a poisonous gas that affects birds’ lungs — usually fatally. Birds provide a particular challenge for veterinarians because they seldom look sick until they are very sick. At that point, it’s often too late.

Roberta Pattison is a freelance writer who is a regular contributor to the national publication, Dogs in Canada. Retired from grain farming, she still lives on her farm near Delisle, Saskatchewan.


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