By Alyssa Blaustein, VMD
MSPCA-Angell West, Waltham
Zinc is an essential element in mammals but is normally present in very low quantities. While having too little zinc in your pet’s diet is detrimental, excessive zinc ingestion may lead to acute zinc poisoning and death. Dogs and cats are most at risk of zinc toxicosis from ingesting a U.S. penny minted after 1982. The penny’s production process was changed in 1982 and pennies now consist of 97.5% zinc with a copper coating. Some Canadian pennies and euro coins can also contain zinc.
The most at-risk populations are small breed dogs, due to their size (foreign objects can pass more quickly through the gastrointestinal tract of larger dogs), and the higher likelihood of dogs ingesting foreign objects than cats. Other potential sources of zinc are galvanized metallic objects (such as nuts, bolts, staples, nails, toys, jewelry, board game pieces, and zippers) and various ointments/lotions (some diaper rash creams, shampoos, sunscreens, and deodorants). Unfortunately, zinc is rapidly absorbed due to the stomach’s strongly acidic environment and is then widely distributed throughout the body.
Diagnosis of zinc toxicosis in your pet relies on a history of potential exposure, including the presence of a metal object seen on x-rays, with compatible clinical signs and blood work abnormalities. Signs associated with excessive zinc ingestion can occur as soon as two hours after ingestion, but may also be delayed. Initially, gastrointestinal distress such as vomiting, anorexia, diarrhea (possibly with blood), depression, and lethargy are seen due to the corrosive properties of zinc. Most topical products containing zinc only cause these gastrointestinal signs. However, hemolysis (destruction of red blood cells) can also occur in the following hours to days. This presents as pale or yellow gums, fast heart rate or breathing, continued gastrointestinal signs, abdominal pain, severe depression, fever, drunk walking (ataxia), seizures, collapse, discolored urine, or decreased urine production. It is also important that your veterinarian consider other possible causes of similar hemolysis when evaluating your pet. These include immune mediated disease, onion or garlic toxicosis, ingestion of other metals, acetaminophen (Tylenol) ingestion, ingestion of some species of mushroom, and poisonous snake bites.
Full blood work and urine testing should be performed by your veterinarian in cases of suspected zinc toxicosis. Anemia (low red blood cell count) and abnormally shaped red blood cells are commonly seen, in addition to many other abnormalities, such as elevations in liver, kidney, or pancreatic values, which can be an indication of disease severity. In the case of hemolysis with an unknown cause, patients should always have an x-ray taken to look for the presence of metallic foreign objects within the gastrointestinal tract. However, not seeing a metallic object on an x-ray does not rule out the possibility of zinc toxicosis. Many patients can vomit up or defecate out foreign objects after significant amounts of zinc have been absorbed. Diagnosis can also be assisted by testing zinc concentrations in the blood.
Treatment is generally supportive in nature. Removal of a metallic foreign object via making the patient vomit, surgery, or endoscopy is imperative if possible. Zinc levels in the blood drop dramatically if there is an object that can be removed. Other treatment recommendations include gastrointestinal protectants, anti-nausea medication, intravenous fluids, and possibly blood transfusions. Chelation therapy (giving a medication that will bind zinc) can also be considered if there is no foreign object to remove, but there is little literature available regarding its efficacy. Prognosis depends on the ability to control the red blood cell destruction and prevent long term organ damage. Zinc toxicosis can be fatal, especially without proper treatment. However, prognosis is good if the source of zinc can be identified and removed. Please contact a veterinarian or poison control if you think your pet has potentially been exposed.