Zinc Toxicity

Some animals can’t resist chewing on metallic objects. In this article, Megan Brashear, CVT, VTS(ECC), outlines zinc toxicity and highlights a recent case seen at DoveLewis.

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Find a penny pick it up…wise words to live by, unless you’re a dog. Some dogs (and cats!) can’t resist the shiny allure of pennies and if they happen to ingest pennies minted after 1982 they can pay the price in the form of a deadly toxicity.

Pennies made after 1982 are made of zinc and only coated with copper. Once a penny hits the acidic environment of the stomach, erosion of the copper layer starts and zinc is released into the animal's system. Because pennies are relatively heavy they can hang around in the stomach for days without passing into the intestines and slowly leak poison until they are completely dissolved. Other products can cause zinc toxicity (pipes, wires, metal fixtures made with zinc or zinc oxide ointments), but pennies are the most common source of the toxicity.

The clinical signs of zinc toxicity start as non–specific gastro–intestinal signs such as vomiting, diarrhea and lethargy. Cells in the GI tract are susceptible to direct damage from the zinc and this irritation causes the early signs of toxicity. Patients in the early stages of toxicity need fluid therapy to reverse their dehydration, removal of the source of zinc, and monitoring of hepatic and renal blood chemistry values. In many cases, drugs to decrease the amount of stomach acid produced (to slow the destruction of the penny) are given before the penny is removed.

If penny ingestion is suspected, the animal should have radiographs taken to confirm the diagnosis. If metallic foreign bodies are seen, the animal needs to have them removed as soon as possible. Some animals will vomit the pennies either on their own or with assistance from the veterinary team, but because of the weight of the pennies, it’s not a given result that vomiting will remove all of them. Radiographs should be taken post–vomiting to be sure they are all cleared from the stomach. Endoscopy can be a tool to remove pennies although this can be a challenging method depending on the tools available to grasp and remove the pennies. An abdominal exploratory surgery is often needed to be sure the offending coins are removed and a necessity if the coins have moved into the small intestine. Depending on how sick the animal is, it may take many hours of hospitalization before they are stable enough for surgery. If the pennies have moved into the colon the animal should have an enema to expedite the removal of the offending coins from the body.

As the disease progresses animals will develop hemolytic anemia and will have direct cellular damage to their liver and kidneys. These patients will present with icterus, hematuria, low PCV, and if untreated will progress to multiple organ failure and death. These clinical signs are almost identical to those of immune mediated hemolytic anemia so patients assumed to have IMHA should be evaluated for zinc toxicity. These patients need fluid therapy to flush the toxin from their system, and depending on the level of their anemia, may need blood transfusions until their PCV stabilizes. Those patients with severe disease are in danger of DIC and should have their clotting ability monitored and may need transfusions of fresh frozen plasma.

Recently a 2 year old female Lhasa Apso presented to DoveLewis with a 24 hour history of increasing lethargy, vomiting and hematochezia. She was known to ingest metal objects. On presentation she was obtunded and significantly dehydrated, had icteric mucus membranes, a PCV/TS of 15%/8.0g/dl (hemolyzed serum) and an increased TBili of 7.1mg/dl (normal 0-0.9mg/dl). Her clotting times were also elevated (PT 13sec normal 9-12 sec; aPTT 222sec normal 59-87 sec). Radiographs revealed multiple round metallic objects within the stomachRadiographs revealed multiple round metallic objects within the stomach. Zinc toxicity was high on the list of rule-outs and the treatment goals became to stabilize the dog prior to surgical removal of the metallic objects.

A blood transfusion of both pRBC and FFP was administered and brought the dog's PCV/TS up to 19%/7.0mg/dl. Her aPTT was rechecked and had decreased to 119sec (normal 59-87 sec). Her mentation had not significantly improved but her vital signs were holding steady from admit and she was deemed stable enough for general anesthesia. The surgeon was unsuccessful with endoscopy to remove the coins (they were identified during endoscopy but unable to be removed) so a gastrotomy was performed. The dog had ingested 39 cents (1 quarter, 1 dime and 4 pennies). During surgery she required a bolus of more pRBC and FFP but her vitals were stable by the end of the procedure. She was started on famotidine and sucralfate for GI protection. 12 hours after the coins were removed her PCV/TS was 27%/6.8g/dl; TBili had decreased to 1.2mg/dl (normal 0-0.9mg/dl); and the aPTT had normalized. The dog had significant gastroenteritis from the coin ingestion and needed multiple days in the hospital to recover but she eventually returned home and is now doing well.

Even after the source of the zinc is removed the animal may still require days of hospitalization until they have healed from the effects of zinc toxicity. Some patients require chelation (giving a substance that will bind to the zinc and remove it from circulation) with calcium EDTA, but this can cause further damage to the kidneys so monitoring renal values and proper fluid therapy are very important. Frequent monitoring of vital signs, monitoring of PCV, renal and hepatic values, and nursing care to keep the patient clean and comfortable are vital to the survival of those patients with zinc toxicity. Owners should be made aware of the dangers of penny ingestion and any animal that ingests an unknown metal object should be watched carefully for signs of zinc toxicity. Technicians should be alert to the possibility of zinc toxicity and play a vital role in educating clients and treating these patients.

Is zinc toxicity something you regularly see in your patients?
Are you educating owners about the dangers of zinc ingestion?

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