Jeffrey Vogl, DVM
Ask the Veterinarian
8:00 PM EDT, April 13, 2011
Q: If my cat has had one bout with toxicity from ingesting onions, is she at greater risk if she ever eats them again? After all, aren't onions natural?A: “So is the Western North American Destroying Angel mushroom, but I am not going to put it on my pizza,” I reply. One bite of this lovely, white, all natural, organic, holistic, free range fungus and you will be pushing up mushrooms.
Though not as poisonous as this mushroom, plants of the onion family, or Allium species, are considered toxic to pets, especially cats. Including onions, garlic, chives, leeks and scallions, these plants contain toxic compounds called sulfoxides that are absorbed through the intestines.
Toxicity varies with the amount and type of Allium ingested; raw, crushed, dried, even cooked Allium can all pose a risk to pets. Fresh onions are 85% moisture and are not as toxic as the dried concentrated forms. The primary toxic mechanism of action is damage to red blood cells, specifically the membrane. This makes the red cells fragile, causing them to rupture which results in anemia (lack of red blood cells). Symptoms in pets, occurring 24-72 hours after ingestion, are directly related to the degree of anemia observed: pale gums, weakness, rapid breathing, rapid heart rate, staggering and collapse.
Most cases of onion poisoning are accidental ingestion of cooked foods containing fresh or dehydrated onion products. Though cats are much more sensitive, exposures are more commonly reported in dogs. Feeding baby food with onion flavoring is a common route of exposure in cats. Obviously, only use onion-free baby foods. The dose of onion exposure is what determines if there will be any clinical signs. It has been reported that 5 g/kg body weight of onion exposure in cats and 15-30g/kg in dogs can cause clinical signs. Another report finds that ingesting .5% of their body weight in onions can be toxic.
To put this into perspective a 10-pound dog would have to eat about 30 grams of onions, which is about two tablespoons.
Diagnosis is typically made from history, clinical signs, blood tests and microscopic confirmation of the type of anemia, called Heinz body anemia. There is no specific antidote for onion toxicosis. Treatment involves inducing vomiting and giving activated charcoal to absorb the toxin if ingestion was within hours. If it has been days and there are clinical signs present, then the treatment is supportive care, including IV fluids, blood transfusions, supplemental oxygen and antioxidants to help the red blood cells. Over time your pet’s body will excrete the toxic sulfoxides completely and there will be no residual effects or increased risks if there is a future exposure.
Just because it’s all natural doesn’t make it safe. The Animal Poison Control Center still receives cases of Allium toxicity from owners using garlic or onion as a remedy for what “ails” their pets.Remember, Dr. Google can be helpful, but you might want to get a second opinion.
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