Oxalates (Soluble) Poisoning in Dogs

Oxalates are a poisonous chemical that occurs naturally in a variety of plants. Oxalates may be either soluble or insoluble depending on the species. After ingestion, soluble oxalates are quickly absorbed into the bloodstream and can cause systemic problems, versus insoluble oxalate crystals which are associated with surface irritation of the skin and the gastrointestinal tract. Both types of poisoning can be serious and even fatal in severe cases.

Soluble oxalates are essentially sodium and potassium salts containing oxalic acid. This type of oxalate binds with calcium (Ca) and magnesium (Mg) ions in the blood limiting the availability of these important electrolytes. This leads to very low levels of available blood calcium (hypocalcemia) which can cause sudden drastic metabolic imbalance. Calcium oxalate is excreted by the kidneys (this is the same substance that causes certain kinds of kidney stones), so very large amounts can produce kidney dysfunction and even fatal kidney failure.

Many fruits and vegetables consumed for food contain low levels of soluble oxalates, including spinach, broccoli, and Brussel sprouts. Others like rhubarb and starfruit have a higher oxalate content, but they are still considered safe for humans unless kidney dysfunction is already present. In the case of rhubarb, the oxalate content is much higher in the leaves which are never consumed for food. These plants can be toxic to dogs because of metabolism differences and smaller size. Serious poisoning is rare, since dogs don’t usually consume large amounts of fruits and vegetables, and many plants with high oxalate content (such as rhubarb leaves) have a bitter, acidic taste which is unpleasant to dogs. Small amounts of soluble oxalates can be processed and excreted in dogs with healthy kidneys; studies have found few negative side-effects with a .5% injection of pure oxalate in dogs and other small animals. However long term consumption will put unnecessary stress on the kidneys and accidental overdose can cause abnormal heart rhythms, muscle weakness, and death from respiratory paralysis in severe cases. Most instances of soluble oxalate poisoning can be treated by a veterinarian.

Soluble oxalates are a toxic component that is found in a number of plant species. This type of oxalate is absorbed into the bloodstream where it can cause metabolic imbalance and kidney failure. Rhubarb and starfruit are some common plants associated with soluble oxalate poisoning in dogs.

These are the symptoms you will see in dogs that have consumed high levels of soluble oxalates.

• Lack of appetite
• Hypersalivation
• Vomiting
• Diarrhea
• Lethargy
• Weakness
• Abnormal heart rhythms
• Tremors
• Blood in the Urine
• Signs of kidney failure - Excessive thirst (polydipsia) and frequent urination (polyuria)

Types

These are some plants that can cause soluble oxalate poisoning in dogs.

Rhubarb (Rheum rhaponticum)

• The edible part, the stalks, contain much less oxalate than the leaves
• All parts of the plant could be toxic to dogs

Shamrock (Oxalis species)

• Also called sorrel, this plant can be eaten by humans but the oxalate makes it toxic in large doses, especially for those with kidney dysfunction
• More than a few leaves could be poisonous for dogs, depending on the size

Dock (Rumex species)

• A common weed with a high soluble oxalate content

Starfruit (Averrhoa carambola)

• Safe for humans, except for those with kidney dysfunction
• Toxic for dogs

These are some of the risk factors for soluble oxalate poisoning.

• Owners mistakenly feeding fruits and vegetables that contain oxalates to their dogs are not aware of the danger to the system
• Dogs eating these foods from the floor or the garbage are not discriminatory in their choices
• Dogs eating plants that contain soluble oxalates such as rhubarb leaves or dock may have gastrointestinal pain and irritated skin

Seeing your dog eat a plant or food that contains soluble oxalates is the best way to diagnose this condition. Otherwise, symptoms of weakness and lethargy combined with low calcium levels on a blood test could help the veterinarian pinpoint the problem. Signs of kidney dysfunction may also be evident, especially with chronic exposure. All of these symptoms could be indicative of many different conditions, so diagnosis will be faster and easier if you know your dog consumed a plant that is high in oxalates. Ethylene glycol poisoning produces calcium and magnesium oxalate in the blood as well, so this will need to be ruled out if you’re not sure what toxic substance your dog may have consumed.

It’s a good idea to call an emergency veterinary clinic or a poison helpline any time your dog eats something that could be toxic. Be prepared with all the information you have about the plant or food, an estimate of how much you think was ingested, as well as your dog’s size and weight. Other medical conditions, especially kidney problems, are also relevant. If a large amount was ingested, you should take your dog to see a veterinarian in person as soon as possible.

For immediate treatment, rinse out your dog’s mouth with milk or water and try to get him to drink some fluids. Don’t induce vomiting unless recommended by a professional.

At the veterinary office, emesis will likely be induced especially for recent poisoning. Activated charcoal is frequently given to reduce absorption. Cathartic medication can also help to produce bowel movements and excrete the plant material before all the nutrients are processed in the gastrointestinal tract.

Intravenous fluids and appropriate electrolytes will help to balance the calcium levels in your dog blood and reduce muscle weakness and paralysis. Other medications may be given to treat tremors and help to support kidney function. In severe cases, dialysis could be needed to help the kidneys process excessive amounts of oxalate.

In general, dogs recover from soluble oxalate poisoning, but this will depend on the amount that was ingested. Fatal poisoning is rare, given the typical oxalate content found in plants and the dietary habits of dogs; however it is possible with high enough doses, especially if kidney dysfunction is already present. Dogs that eat large quantities of fruits, vegetables, or plants when unsupervised are most at risk, as well as small dogs as they will have more trouble processing small amounts of oxalate.

To manage the condition, avoid feeding fruits and vegetables to your dog. Dispose of spoiled food or unused plant parts (such as rhubarb leaves) in a sealed garbage can. Discourage your dog from eating plants if possible. If not, try planting dog safe plants like wheat grass so your dog will have something to chew on that isn’t toxic.