Rodenticide Poisoning in Cats

Rodenticide poisoning is the accidental ingestion of products used to kill "rodents" such as mice, rats and gophers. These products are common and accidental exposure is frequent. Poisoning is most commonly caused by ingestion of a product containing one of the following ingredients:

• Bromethalin
• Cholecalciferol (Vitamin D3)
• Strychnine
• Zinc phosphide
• Anticoagulant (warfarin, fumarin, chlorophacinone, diphacinone, difethialone, pindone, bromadiolone, brodaficoum)

Younger and older pets tend to be more sensitive to the affects of toxicity and underlying liver disease can exacerbate toxicity.

The impact on the poisoned animal varies depending on the type of poison ingested. An animal may develop a bleeding disorder, neurological problems, gastrointestinal distress or kidney failure. In some cases, rodenticide poisoning is fatal.

What to Watch For

• Depression
• Lethargy
• Bleeding
• Loss of appetite
• Vomiting
• Diarrhea
• Increased thirst or urinations
• Lameness
• Incoordination
• Difficulty walking
• Collapse
• Difficulty breathing
• Extreme sensitivity to light
• Noise or touch
• Seizures
• Coma
• Sudden death is possible

Diagnosis

There is no single test that can be performed to make a definitive diagnosis of rodenticide poisoning. However, in addition to a thorough history and physical examination, your veterinarian may recommend one or more of the following tests to aid in the diagnosis.

Tests may include:

• A complete blood count (CBC)
• A serum biochemical profile
• Urinalysis
• Examination of stomach contents
• Platelet count
• Reticulocyte count
• PIVKA (for anticoagulant rodenticide ingestion)
• Clotting tests, such as: an activated clotting time (ACT) test, a prothrombin time (PT) test and an activated partial thromboplastin time (APTT) test

Treatment

Therapy for rodenticide poisoning varies based on the type of poison ingested, the amount ingested and the length of time elapsed since ingestion. Treatments may include one or more of the following:

• Vomiting should be induced if ingestion was recent.
• Activated charcoal can be administered to bind poison remaining in the stomach.
• Gastric lavage (pumping the stomach)
• Intravenous fluids

Additional treatments may include:

• Anticonvulsant drugs
• Blood transfusion
• Muscle relaxants
• Drugs to treat kidney failure such as furosemide and dopamine
• Drugs to reduce swelling of the brain such as mannitol and steroids
• Vitamin K1
• Oxygen
• Heat support
• Nutritional support
• Cage rest
• Antibiotics may be prescribed if a concurrent infection is identified or suspected.

Home Care and Prevention

Prevent exposure to poisons. If you normally use rodenticides, store them with special care. When poisons are used, place them in areas in which your pets do not have access. Take special care as rodents may drag poisons within reach of pets. Remember that cats can often crawl in unlikely areas, especially if they smell other animals such as rodents.

Keep your cat indoors to minimize exposure to other people's poisons.

Many diseases mimic rodenticide poisoning. The exact types of symptoms and problems your pet will exhibit depends on the type of poison. The general types of poisons include:

• Anticoagulent rodenticides, which are poisons that interfere with blood clotting
• Bromethalin-containing rodenticides
• Poisons containing strychnine and metaldehyde
• Cholecalciferol-containing rodenticides
• Zinc phosphide-containing rodenticides

Anticoagulant rodenticides

These products may cause prolonged bleeding from cuts; bloody vomit or diarrhea; hematomas (swellings under the skin containing blood); lameness due to bleeding into joints; joint swelling; rapid or labored breathing due to bleeding into the chest or lungs; weakness; collapse; and sudden death. Diseases that cause similar symptoms include the following:

• Hemophilia is a bleeding disorder that dogs may be born with and may cause hematomas, bleeding into joints, and prolonged bleeding following bites, cuts and surgical procedures.
• Immune mediated hemolytic anemia (inappropriate red blood cell destruction by the pet's immune system) can cause anemia.
• Immune mediated thrombocytopenia (inappropriate platelet destruction by the pet's immune system) can cause anemia, prolonged bleeding following bites, cuts and surgical procedures as well as spontaneous bleeding or bruising.
• Severe liver disease may cause anemia and prolonged bleeding times.

Bromethalin-containing rodenticides

These products may cause severe muscle tremors, hyperexcitability, running fits, extreme sensitivity to being touched (hyperesthesia) and seizures that appear to be caused by light or noise. Less frequent symptoms include loss of ability to bark, loss of appetite, depression, lethargy and coma. Conditions that can look similar include:

• Poisons containing strychnine and metaldehyde (slug bait) can cause muscle tremors and hyperexcitability. Strychnine is no longer commonly used for pest control and is rarely encountered. Slug bait toxicity is most common on the west coast of the United States.
• Neurological diseases that cause seizures such as epilepsy and Granulomatous Meningo-encephalitis (GME).
• Ingestion of compost or moldy garbage may cause severe muscle tremors, hyperexcitability and seizures and is easily confused with bromethalin poisoning.
• Salt poisoning causes abnormally high sodium levels in the blood and can lead to muscle and head tremors and eventually coma and death if uncorrected.

Cholecalciferol-containing rodenticides

These products may cause increased thirst, increased urinations, vomiting, diarrhea, lethargy, loss of appetite and constipation. These signs are attributable to the effects of elevated calcium levels in the body and accompanying kidney failure.

• Certain types of cancer: such as lymphosarcoma, anal sac carcinoma, mammary gland or nasal cavity carcinoma, thyroid carcinoma and testicular carcinoma are capable of causing elevations of calcium in the body with subsequent kidney failure.
• A history of exposure is the single most important diagnostic tool. If the owner of a poisoned pet witnesses the ingestion or can produce the remnants of containers or labels, this greatly limits the need to look for other causes.
• Your veterinarian should complete a thorough physical examination to look for evidence of bleeding such as swollen joints, hematomas (swellings under the skin containing blood) or pale gums indicating anemia (low red blood cell count).
• A complete blood count (CBC) is obtained to look at the characteristics of the red blood cells. The CBC helps determine whether the loss of red blood cells has been sudden (more consistent with poisoning) or chronic.
• A serum chemistry profile is helpful to eliminate kidney or liver problems, both of which can cause anemia or bleeding problems.
• A platelet count is important to rule out bleeding from low platelet levels, which can be caused by other diseases.
• A reticulocyte count determines whether the animal's body is trying to regenerate red blood cells that have been lost.
• A PIVKA (Proteins Induced by Vitamin K Absence or Antagonists) test is a blood test that can be collected by your veterinarian and sent to a lab to determine if bleeding is due to exposure to anticoagulant rodenticides. Because this test is performed in a lab outside of your veterinarian's hospital, the results may take several days.
• Clotting tests such as an activated clotting time (ACT), prothrombin time (PT) and activated partial thromboplastin time (APTT) are used to determine if anemia and/or bleeding are due to the inability of the animal to clot its blood. These values are greatly prolonged in anticoagulant rodenticide poisoning. As the pet is treated, your veterinarian will likely repeat these blood tests to confirm that they normalize.
  Bromethalin, cholecalciferol, strychnine and zinc phosphide-containing rodenticides
• A history of exposure, observation of symptoms associated with these types of rodenticide poisoning and a thorough physical exam are the best diagnostic tools.
• A CBC is usually done to evaluate for infection or inflammation as potential causes for the pet's symptoms.
• A serum biochemistry profile helps to evaluate the kidneys and liver for evidence of failure. Abnormalities in electrolytes such as sodium will also be detected with this test.
• Examination of stomach contents or vomit may raise the suspicion of poisoning or identify the remnants of the poison ingested and a pet owner can be sent home to look for evidence of a chewed package to confirm the diagnosis.

Treatment In-depth

Depending on the amount of rodenticide ingested, type ingested and the length of time elapsed since ingestion treatment varies. Some patients may be treated on an outpatient basis while others require hospitalization. Treatments for rodenticide poisoning may include one or more of the following:

Standard treatment for poisoning (if within 4 to 6 hours of ingestion) includes:

• Administering either apomorphine (a powder placed in the corner of the eye) or hydrogen peroxide orally to induce vomiting. Induced vomiting removes undigested poison from the stomach.
• Activated charcoal to absorb any poison remaining in your pet's stomach or intestinal tract after induced vomiting or gastric lavage. A cathartic is often administered after the charcoal to help speed movement through the digestive tract and elimination. Activated charcoal is administered via a stomach tube or is syringe fed to the animal.
• Pumping the stomach. If your pet cannot be induced to vomit, the dog's stomach can be pumped. During this procedure, a large tube is passed through the mouth to the stomach. Water is pumped into the stomach and then drained, removing any stomach contents. This procedure requires heavy sedation.
• Administering intravenous fluids to correct dehydration from vomiting or diarrhea and to aid in the removal of some poisons and protect the kidneys from damage.

In addition to the standard treatment for poisoning, each type of rodenticide requires different treatment approaches because each poison affects animals differently.

For anticoagulant rodenticide, these may include:

• Additional therapy may not be required if the poison is removed from the stomach.
• Administration of Vitamin K is necessary to replace the Vitamin K, which cannot be made by the body due to interference by the rodenticide. Vitamin K therapy is initiated in hospital and is then continued at home for a total of 3 to 5 weeks.
• A blood transfusion will be administered if the pet has lost a large amount of blood, due to bleeding, and is anemic.
• A plasma transfusion often is given to replace missing clotting factors when the pet's bleeding times are greatly prolonged. This helps to prevent additional bleeding while waiting for the Vitamin K to work (usually 24 to 36 hours).

For bromethalin containing rodenticides, treatment may include:

• Drugs such as mannitol and/or steroids are used in an attempt to control cerebral edema (swelling of the brain) that occurs with this type of poisoning. These drugs often require repeated intravenous administration.
• Anticonvulsant drugs such as diazepam (Valium®), phenobarbital and pentobarbital are used to control seizures and severe muscle tremors, as well as to promote muscle relaxation.

For cholecalciferol containing rodenticides, these may include:

• Drugs such as furosemide, steroids and calcitonin may be used in conjunction with intravenous fluids to reduce serum calcium levels. Furosemide and steroids are used predominantly. Calcitonin is used when the other drugs are not sufficient to control calcium levels alone.
• Furosemide and dopamine are administered to promote blood flow to the kidneys and to increase urine output during kidney failure.

For strychnine, these may include:

• Muscle relaxants are necessary to allow the animal to relax rigid muscles and legs.
• Anticonvulsants such as Valium®, phenobarbital and pentobarbital are used to reduce or prevent seizures that accompany strychnine poisoning.

For zinc phosphide containing rodenticides, these may include:

• There is no definitive treatment for zinc phosphide containing rodenticides; therefore treatment is directed at removing the poison from the digestive tract and general in-hospital supportive care.