Toxic Foods

Toxic foods and common household products

Even within the safety of our own home, there are many potential dangers to our pets. Bringing awareness of common hazards will help to ensure owners consult their vet before self-prescribing with human medications or offering unsuitable snacks.
Encouraging owners to store medications securely (including those prescribed by the vet) and monitoring small children with food would also be wise, given the list of frequently encountered toxins.
Whether or not the owner is sure what has been ingested, the best course of action is always to come to the clinic as soon as possible for examination. If packaging/photographs or a data sheet is available with the suspected ingested substance, this can assist with treatment and investigation.

FOODS

Apple and pear seeds

The seeds or pits contained within apples, pears, apricots and plums contain amygdalin, a glycoside that degrades to release hydrogen cyanide. In reality, the toxic dose in dogs and cats is greater than they are likely to ever consume. The seeds also need to be ground into a powder to release the glycoside which is unlikely following normal mastication and digestion. Seeds tend to pass through the intestinal tract in their complete form.

It is recommended to remove the core when offering apple to pets, but the risk of toxicity with accidental consumption is extremely low.

Avocados

Avocados are toxic to most animals- including dogs and cats. The fungicidal compound persin is found in varying concentrations in the leaves, bark, pit and fruit and can cause myocardial damage and mastitis in lactating animals (1). Large quantities would need to be consumed in order to cause symptoms, with the exception of birds which are known to be much more sensitive. Symptoms seen after consumption include vomiting, diarrhea, dysrhythmias and respiratory distress. Symptomatic treatment should be enough to assist recovery in most cases.

Bread dough (2)

If raw bread dough is eaten, the ideal conditions for fermentation can be found within the stomach. Bread dough can therefore result in gastric distension and potentially impaction or volvulus due to expansion in the stomach. The dough rises, due to production of carbon dioxide and ethanol during metabolism of the sugars in flour. Metabolic acidosis and decreased mentation can be observed following absorption of ethanol. Treatment includes supportive therapy with diuresis, correction of acid-base disturbances and maintenance of body temperature. Gastric lavage rarely can remove the dough from the stomach, alternatively supportive therapy until the dough passes through the intestinal tract is the mainstay of treatment. Occasionally surgery may be required to remove the dough- in cases of dilatation and in breeds predisposed to volvulus.

Chocolate

Caffeine and theobromine are methylxanthines found in chocolate which can be toxic to dogs, cats, rabbits and parrots and should be avoided in all these species in any amounts. Individual sensitivity varies and so complete restriction is advised.

Dark and baking chocolate tends to contain more theobromine than milk chocolate. Methylxanthines increase intracellular calcium levels and result in increases in strength and contractility of cardiac and skeletal muscle (3) which explains many of the presenting clinical signs. Clinical signs include excessive thirst, hyperactivity, diarrhea, tachycardia, hyperthermia, tremors and seizures. If untreated, toxicity can lead to cardiac arrest.

The Merck Veterinary Manual offer a toxicity calculator to clinicians to assist in treatment if body weight and type of chocolate consumed are known (4). Rapid decontamination if possible, with gastric lavage is recommended, otherwise supportive treatment and electrolyte monitoring must be a priority.

Macadamia nuts

Macadamia nuts have been noted to cause vomiting, ataxia and depression in dogs following ingestion. Ingestion of 2.4g/kg has resulted in clinical signs (5). These generally resolve within 12-48 hours without intervention and toxicity is not fatal.

Grapes and raisins

Consumption in dogs can cause anuric renal failure (6). The sensitivity varies between individual dogs and the mechanism of toxicity is currently unknown. The proximal renal tubular epithelium has been determined to be most damaged after ingestion.

As few as 4-5 grapes have been reported to cause death in an 8kg dog and as such it is recommended to avoid completely (6). Clinical signs are usually noted within 6-12 hours of ingestion and anorexia, lethargy, abdominal pain and polydipsia have all been described in the early stages. Supportive therapy should be started immediately but the prognosis remains guarded. Renal failure after grape/raisin ingestion has been anecdotally reported in cats.

Other species such as rabbits and parrots show no toxic effects and regularly enjoy grapes and raisins as a treat.

Xylitol is an artificial sweetener found in baked goods, candy and chewing gum and can cause release of endogenous insulin in dogs due to hypoglycaemia. Dosages of 75-100 mg/kg have been associated with toxicity (7). Clinical signs following ingestion can be noted as soon as 30 minutes after ingestion and include vomiting, ataxia, depression and seizures. Charcoal does not effectively bind Xylitol. In more severe cases, hepatotoxicity can occur. Electrolyte disturbances noted include hypokalaemia and hyperphosphataemia, with the latter considered a poor prognostic indicator.

Treatment should be aimed at managing the hypoglycaemia and monitoring liver parameters and dogs with known ingestion should be hospitalized to monitor over 24-48 hours. Charcoal does not effectively bind Xylitol.

Xylitol toxicity has only been reported in dogs (7).

Onions and garlic

The allium family is extensive and includes onion, garlic, shallots, chives and leeks as well as ornamental plants such as daffodils. All forms can be toxic- cooked, raw, dried or powdered as they all contain thiosulphate.

Excessive ingestion will cause toxicity in dogs, cats, rabbits and parrots. Some breeds of dogs are more sensitive than others and cats are more sensitive than dogs. Ingestion causes general gastrointestinal irritation, resulting in hypersalivation, vomiting and diarrhea. Oxidative damage to red blood cells occurs and the resulting haemolytic anaemia will lead to weakness and fatigue. Clinical signs include lethargy, haemoglobinuria, tachycardia, ataxia and panting. Collapse and syncopal episodes may also be the reason for presentation to the clinic. In severe cases, transfusions may be necessary.

Rhubarb

Rhubarb or Rheum rhabarbarum leaves contain soluble calcium oxalate crystals and oxalic acid. Ingestion in large enough quantities will result in hypocalcaemia and irritation in the mouth, diarrhea and abdominal discomfort. Dogs and cats rarely eat the leaves due to their bitter taste, but rabbits may be tempted, so access to the plants should be restricted.

DISINFECTANTS, CLEANING AGENTS AND MEDICATIONS

Dettol

The active ingredient in Dettol is phenol chloroxylenol and is dangerous to all animals if ingested, but particularly to cats due their inability to metabolize it if ingested. Commonly cats will lick the product off their paws if used within the home, rather than direct ingestion. Clinical signs include hypersalivation, ulceration to the mucous membranes, anorexia and organ failure. Bathing after exposure and application of a buster collar to prevent grooming must be immediate with supportive therapy and diuresis as clinical signs become more apparent. A nasogastric or oesophageal feeding tube may be required until inflammation of the upper gastrointestinal tract settles.

Permethrin

Permethrin poisoning in cats occurs when ectoparasite products for dogs are mistakenly applied to cats. Cats lack glucuronidase, the enzyme necessary to metabolise pyrethrins and so the drug accumulates. The neurological symptoms progress from tremors, seizures and photosensitivity to eventual coma and toxicity carries an extremely poor prognosis. It is extremely important that products containing permethrin are clearly labelled to avoid confusion and inappropriate use.

HUMAN MEDICATIONS SHOULD NEVER BE GIVEN TO ANIMALS WITHOUT PRIOR DISCUSSION WITH THE VETERINARIAN

Acetaminophen (Paracetamol)

Cats are also unable to metabolize acetaminophen, a common non-steroidal anti-inflammatory drug (NSAID) available in supermarkets. This drug causes both methaemoglobinaemia and hepatotoxicity. Cats that have ingested acetaminophen will commonly show symptoms within 1-4 hours of ingestion.
Abdominal pain and nausea may be seen, and cyanosis of the mucous membranes as methaemoglobinaemia occurs.
Death can occur within 18-36 hours of ingestion of the drug and as little as 10mg/kg can be toxic to cats compared to 75-100 mg/kg in dogs (8).

There is an antidote N-acetylcysteine (a precursor to glutathionine) which is used to scavenge the reactive metabolites. This must be given alongside aggressive supportive management to prevent excessive absorption of acetaminophen in order to be successful. Liver support may also be required long term to aid recovery. Unfortunately, often the prognosis in these cases is grave.

Ibuprofen

Another human NSAID contraindicated in cats and dogs is Ibuprofen. Ibuprofen decreases pain and inflammation by blocking the COX-1 and COX-2 (cyclo-oxygenase) enzymes which catalyzes the conversion of arachidonic acid to prostaglandins (inflammatory mediators). COX -2 has been found in endothelial cells and macrophages and is upregulated at sites of inflammation. COX-1 enzymes however, produce prostaglandins that have a positive effect in the body- such as prevent ulcer formation in the stomach and gastrointestinal tract, and as an essential part of the clotting cascade (9).

Animals with pre-existing renal or gastrointestinal disease will be much at risk of toxicity. Dogs and cats are also unable to metabolize ibuprofen and so the drug remains in the system at higher doses than it would in humans. Clinical signs can range from abdominal pain, vomiting and anorexia to petechial haemorrhages, melaena and renal failure. The prognosis is grave with supportive symptomatic treatment, unless presented within the window of time that allows the drug to be evacuated from the gastrointestinal tract.

FLOWERS AND HOUSEHOLD PLANTS

Lillies

They may be beautiful to look at, but many varieties of lilies including Easter, Tiger and Asiatic varieties are extremely toxic to cats. Ingestion of even just a small amount of the leaves or the flowers can be fatal. Ingestion results in acute tubular necrosis and renal failure and clinical signs can occur within a few hours after ingestion. Cats may present with hypersalivation, vomiting and anorexia, with progression to polyuria and polydipsia in a few hours. Treatment is aimed at elimination from the stomach if within 1-2 hours post ingestion via gastric lavage and diuresis to support renal function.
Many other flowers and household plants including chrysanthemums, ferns, sweet peas and oleander are also toxic and a more comprehensive list can be found on the Cats Protection UK website (10).
This list is not exhaustive and is aimed to provide concise information and where possible, direct clinicians to further appropriate references.
It is always safest to request the owner presents their animal to the vet as soon as toxicity is suspected, particularly if gastric lavage and decontamination may be an option.
Often the clinic signs can mimic heat stroke, dietary indiscretion or epilepsy, and a detailed history may be required to investigate- but the sooner the animal is presented to the clinic, the better.

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Postdate: 27th Aug 2020

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