Garlic and Onion (Allium spp) Toxicosis in Animals

Allium spp include garlic, onions, chives, and leeks, although garlic and onions are most commonly associated with toxicosis. Garlic is 3–5 times more toxic than onion.

Cats are the most susceptible species, followed by dogs; toxicosis in these species is most commonly associated with ingesting concentrated forms of Allium, such as dehydrated flakes, powders, or dry onion soup mixes. However, toxicosis has been reported in cats after ingesting less than a teaspoon of cooked onions or 5 g/kg of raw onions. In dogs, ingestion of 15–30 g/kg of raw onion has resulted in clinical signs. 

Toxicosis has also been reported in production animals, with goats and sheep seemingly more resistant than cattle or pigs; ruminants can develop a tolerance for Allium spp with a gradual increase in concentration in their feed.

Sulfur-containing oxidants in Allium spp are thought to be responsible for the hemolysis that occurs after ingestion. These compounds are released via mechanical disruption (chopping, cooking, chewing) of the plant and by the action of GI microbes on the material. Absorption of these oxidant compounds results in oxidative damage to RBCs, Heinz body formation, and methemoglobinemia, which begins within 24 hours and peaks in approximately 72 hours. Hemolysis typically occurs 3–5 days after exposure. Hemoglobinuria may result in secondary nephrosis after hemolysis.

Clinical signs of Allium spp toxicosis are generally not noted until substantial hemolysis has occurred, usually a few days after exposure. Lethargy, anorexia, tachypnea, tachycardia, weakness, exercise intolerance, icterus, hemoglobinuria, collapse, and death may occur.

• Clinical evaluation

• Patient's history of exposure

• Heinz body hemolytic anemia, with or without methemoglobinemia

Diagnosis of Allium spp toxicosis relies on patient's history of exposure, clinical signs, and clinicopathological confirmation of Heinz body hemolytic anemia. Methemoglobinemia may or may not be present by the time extensive hemolysis has occurred.

• Early GI decontamination

• Oxygen supplementation or blood transfusion

• IV fluid therapy

Life-threatening clinical signs of Allium spp toxicosis should be managed first with oxygen supplementation and blood transfusion, as needed. IV fluid therapy is recommended to help protect the kidneys against hemoglobinuric nephrosis.

GI decontamination in cases of recent ingestion is recommended. Emesis should be induced via administration of one of the following drugs:

• ropinirole (dogs only; 2.7–5.4 mg/m² in the conjunctival sac, repeated in 20 minutes)

• apomorphine (dogs only; 0.03–0.04 mg/kg, IM, IV, SC, or in the conjunctival sac, although IV is now preferred due to its speed)

• 3% hydrogen peroxide (dogs; 1–2 mL/kg, PO, maximum of 45 mL)

• dexmedetomidine (cats; 7–40 mcg/kg, IM, or 3.5 mcg/kg, IV)

Note: Use of emetic drugs licensed for use in dogs should be prioritized over extra-label use of other drugs to ensure emesis and to avoid unintended adverse events.

Administration of activated charcoal may be considered in cases of Allium exposure in dogs and cats, but whether it adsorbs or prevents production of sulfides derived from Allium is unknown.