Metaldehyde Toxicity (Slug Bait Poisoning)

By Catherine Barnette, DVM

Emergency Situations, Pet Services

What is metaldehyde?

snail_baitMetaldehyde is a chemical that is most commonly found in slug and snail baits. Rarely, metaldehyde can also be found in solid fuels used for camp stoves. Slug/snail baits, which come in both liquid and granular forms, are designed to be placed around walkways and gardens. In order to attract slugs, they are tasty; unfortunately, this taste can also appeal to pets.

What is metaldehyde toxicity?

When pets eat the slug bait, either off the ground or from a storage container, toxicity or poisoning can occur. Metaldehyde is highly toxic, although its mechanism of action (how it causes toxicity) is unknown. A 10-pound (4.5 kg) dog may show signs of toxicity after eating as little as 1 ounce (28 g) of a typical 3% metaldehyde bait.

Metaldehyde toxicity can affect both dogs and cats, though it is far more common in dogs. Metaldehyde toxicity can also affect wildlife.

What are the signs of metaldehyde toxicity?

dog_tremors_poisoning_2018-01Signs of toxicity develop quickly, often within one hour of ingestion. The first sign is usually vomiting, caused by metaldehyde irritating the lining of the stomach.

Next, a number of neurologic signs occur. Affected dogs may become anxious, with a racing heart and increased respiratory rate. They may salivate (drool) more than usual, walk stiffly, or have ataxia (a wobbly, drunken gait due to lack of muscle control and coordination). Many dogs become hypersensitive to touch. As signs progress, affected pets develop muscle tremors; these tremors often cause a high fever that can lead to organ failure. Nystagmus (rapid back-and-forth movement of the eyes) may also occur, especially in cats.

The signs of metaldehyde toxicity progress for several hours after ingestion. Later signs include lethargy/weakness, continuous muscle tremors or seizures, and loss of consciousness.

Toxicity can be fatal without treatment. Pets may develop an inability to breathe properly. In addition, high fever can lead to organ failure.

How is metaldehyde toxicity diagnosed?

Diagnosis is based on clinical signs and a history of suspected exposure to slug bait. Stomach contents can be tested for metaldehyde, but the results of this test are not usually available quickly enough to offer any treatment benefit.

Your veterinarian will likely run a number of laboratory tests, including a complete blood cell count, serum chemistry profile, and urinalysis. These tests are used to rule out other possible causes of your pet’s clinical signs and can also help your veterinarian detect complications that may require treatment (such as changes in the acidity of your dog’s blood, caused by prolonged tremors).

How is metaldehyde toxicity treated?

If your dog has ingested metaldehyde within the last hour, and is not showing any neurologic signs, your veterinarian will induce vomiting. If you live far away from your veterinary clinic, your veterinarian may have you induce vomiting at home, so that treatment can begin before your pet arrives at the veterinary clinic. Your veterinarian will also give activated charcoal, which binds metaldehyde remaining in the intestines and decreases further absorption.

"If your dog has ingested metaldehyde within the last hour, and is not showing any neurologic signs, your veterinarian will induce vomiting."

If your pet is not stable enough to safely induce vomiting, your veterinarian may empty the stomach using a procedure known as gastric lavage. Your dog will be anesthetized and a tube will be passed down the esophagus to the stomach. The tube is used to drain material from the stomach and then flush the stomach with fluid. Activated charcoal will be placed in the stomach to bind remaining metaldehyde.

Even if your dog’s stomach is successfully emptied, he should remain hospitalized for several hours. Your veterinarian will give repeated doses of activated charcoal, to decrease absorption of the toxin. Your pet will also be monitored closely for signs of toxicity.

If signs of toxicity develop, your pet will be hospitalized for a longer course of treatment. There is no antidote to metaldehyde, but supportive care can help keep your pet comfortable and address some effects of this toxin. Medications will be given to control tremors, prevent seizures, and correct blood abnormalities. Intravenous fluids will be given, to keep your pet hydrated. Your dog’s body temperature will be closely monitored and, if necessary, cooling can be provided.

In severe cases, dogs may need to be placed under heavy sedation or anesthesia to control muscle tremors. This sedation or anesthesia may need to be continued for 24 hours or more.

What is the prognosis for metaldehyde toxicity?

With appropriate, aggressive treatment, the prognosis for metaldehyde toxicity is good. Most pets recover fully within 2-3 days, if treatment is started early.

Treatment can be expensive, especially in severe cases that require sedation or anesthesia. This may make aggressive treatment out of reach for some families. For this reason, it is better to focus on the prevention of metaldehyde toxicity than to rely upon treatment.

How can metaldehyde toxicity be prevented?

Slug baits containing metaldehyde should be avoided. Not only can these baits harm your pets, they can also harm wildlife.

"Slug baits containing metaldehyde should be avoided."

To control slugs without metaldehyde, many gardeners recommend using broken shells, lava rock, or other rough materials in flower beds. These materials can deter slugs. Consider using copper bands around plants, or adding lavender, mint, or rosemary to your garden, in order to deter snails and slugs. Shallow cans (such as tuna cans) full of beer can also be used to attract and drown slugs.

There are baits on the market that are considered safer for pets. These products contain iron phosphate instead of metaldehyde. These baits are still potentially toxic, but much larger doses are required and therefore toxicity is less likely than with metaldehyde.

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