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Are both garlic and onions toxic?  What kinds of onions are toxic?

Garlic and onions, as well as other plants of the Allium species (leeks, chives) in either fresh, dried, or powdered forms are toxic to both dogs and cats.

Garlic is more toxic than onions – with raw garlic, toxic ingestion is around 1 gram per pound, and with onions it is 1 gram per 5 pounds.  Onion and garlic powder are more potent and can cause more serious problems than fresh.  Garlic/onion powder can be found in some baby foods, so read these labels carefully if you need to feed baby food to a cat or dog.

How does this toxicity work, and why aren’t garlic or onions toxic to people?

The primary toxic ingredient in garlic and onions is n-propyl disulfide, an oxidant.  Compared to humans, dogs and cats are more sensitive to “oxidative damage” on their red blood cells.  Dogs have more “areas” on their red blood cells that oxidizing agents such as n-propyl disulfide can attach to.  This attachment is recognized by the body as a foreign invader, and in the attempt to remove this invader, the body also destroys the red blood cell.  This is called “hemolysis” – the breaking down of the red blood cells.

What are the symptoms of toxicity?

Anemia (low red blood cells) occur when the hemolysis is severe.  Signs of anemia are weakness, lethargy, and decreased appetite.  They can also have pale gums.  Because red blood cells carry oxygen, acutely anemic pets can “faint” since they are not getting enough oxygen.

The breakdown of the red blood cells can also discolor the urine, so a report of a “port wine colored urine” can be a symptom of hemolytic anemia.

What types of animals are affected?

Dogs and cats, but toxicity has also been reported in wildlife (geese).  Human red blood cells are just tougher than our animal counterparts, apparently.  Cats are more sensitive than dogs – good thing cats don’t usually go chewing on onions or garlic!

How is toxicity diagnosed, and what is the treatment?

Findings of labwork suggestive of Hemolytic Anemia coupled with seeing Heinz Bodies on a blood smear is suggestive of an oxidative toxicosis.  “Heinz Bodies” can be seen on the edges of red blood cells microscopically and these are indicative of oxidative injury.  So a Heinz Body Hemolytic Anemia with a history of snacking on garlic and onions presumes a diagnosis of onion or garlic toxicosis.

There are other causes of Hemolytic Anemia as well, and evaluation of the blood panels or xrays can help determine the correct diagnosis.

Treatment for onion/garlic toxicosis is relatively straightforward – STOP FEEDING THE ONION/GARLIC!  Over a period of time, the bone marrow will readily release more red blood cells in the system, and if no onion or garlic is still being given, then the body will stop hemolyzing the red blood cells.  Treatment is supportive mostly – making sure the pet stays nice and quiet (excitement = panting = not enough red blood cells to carry oxygen = fainting spells!) and eating well (but not onions!).

If severely anemic, then a blood transfusion may be needed.

What’s the prognosis?

Generally good to excellent as long as the insult is not too great.

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