Toxicology Brief: Too much of a good thing: Zinc toxicosis in dogs - Veterinary Medicine
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Toxicology Brief: Too much of a good thing: Zinc toxicosis in dogs
Excessive amounts of this essential mineral can lead to serious consequences, and the condition can easily be mistaken for immune-mediated hemolytic anemia. Be sure to follow these guidelines to detect and treat zinc toxicosis in your patients.


VETERINARY MEDICINE


INCIDENCE AND ABSORPTION

Zinc toxicosis has been reported in domesticated and wild animals, including cattle,10 horses,11 pigs,12 sheep,13,14 dogs,8,15-20 birds,21 ferrets,22 and other wildlife.23 In 2010, the ASPCA Animal Poison Control Center (APCC) reported 4,660 cases of zinc exposure in dogs and 250 cases in cats. Most of these reported sources of zinc were from metallic objects, multivitamins, and zinc oxide creams and ointments.24

To date, multiple case reports and a retrospective study have been published documenting the various clinical manifestations of zinc toxicosis.2,7,8,15-20,25,26 Most of these reports involve ingestion of metallic objects, in particular pennies. A retrospective case series of 19 patients documented that small-breed dogs were overrepresented.15 This overrepresentation may have been due to dose-related effect or because metallic objects could not pass through the pylorus due to small patient size.15 Zinc chloride ingestion has also been reported in the human literature. Symptoms reported included burns of the oral mucosa, pharynx, trachea, esophagus, and stomach; central nervous system depression; nephritis; hemolysis; and pancreatitis.19

Most of the toxic effects of zinc occur when free zinc is released by the stomach's acidic environment. Free zinc forms zinc salts, which are caustic to the intestinal mucosa and absorbed.7 Thus, the longer the object sits in the stomach's acidic environment, the more zinc is absorbed systemically.7 For example, when zinc oxide ointment is ingested in large amounts, it interacts with hydrochloric acid within the stomach to form zinc chloride. The formation of zinc chloride produces irritation and corrosion of the gastric and duodenal mucosa. Thus, vomiting has been reported in dogs that have ingested tubes of zinc oxide ointments or creams.18 In these patients, hemolytic anemia is unlikely since decontamination through spontaneous emesis has occurred. But chronic ingestion of zinc oxide-containing products applied to a patient's skin can be a source of toxicosis as a result of low-dose chronic ingestion over a few days or longer.18

The toxic dose has not been established in dogs. However, normal zinc serum concentrations in dogs are between 0.7 and 2 μg/ml.25

CLINICAL FINDINGS

Zinc toxicosis can cause intravascular hemolysis, pancreatitis, coagulopathies, acute renal failure, and neurotoxicity (scan the QR code to the right or go to http://dvm360.com/ZincEffects to see the important ways zinc toxicosis can cause adverse effects). Most patients begin to exhibit clinical signs within a few days of zinc ingestion. The severity of the clinical signs is usually positively correlated to the dose ingested. Clinical signs can range from mild vomiting to death. For example, reversible cytopenias (anemia and neutropenia) have been documented in people with chronic oversupplementation of zinc.27 Early clinical signs of toxicoses can include vomiting and anorexia, diarrhea, and melena. This is due to zinc-induced gastric irritation.7

Pigmenturia, lethargy, and weakness can occur from intravascular hemolysis.8,15,18,19,20,25 Port wine-colored, pink, or brown urine is commonly noted. Gastric and duodenal ulceration, hepatic dysfunction, pancreatitis, acute renal failure, seizures, coagulopathies, and disseminated intravascular coagulation (DIC) may also occur as a result of zinc toxicosis.8,15-20

PHYSICAL AND NEUROLOGIC EXAMINATION FINDINGS


1. Icteric mucous membranes are evident in this dog secondary to zinc toxicosis.
Physical examination findings often include pale mucous membranes, tachycardia, a heart murmur (secondary to anemia), dehydration, icterus (Figure 1), and abdominal pain.15 Tachypnea, lameness, polyuria, and polydipsia have also been documented.9,15

Neurologic abnormalites can vary from mild lethargy to severe depression. Weakness can be noted. Seizures are possible. Severe neurologic disease (i.e. seizures, vocalizing) is rarely documented in cases of zinc toxicosis. Continuous howling was documented in a puppy that died after ingestion of fragment of a zinc-containing heating pipe.9


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Source: VETERINARY MEDICINE,
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