Zinc Poisoning: This Is Why Pennies Can Harm Pets

Zinc poisoning is relatively common, especially in dogs, perhaps because of their inquisitive natures and tendency to eat things they shouldn’t.

Small dogs seem more susceptible to zinc poisoning, and young dogs are more likely to eat objects that aren’t good for them.

Many household objects contain zinc including zippers, screws, metal work, coins and jewelry. At the top of the list of those

things most commonly eaten that contain zinc are U.S. pennies.

Indeed, pennies minted after 1982 contain around 96% zinc.

But the list doesn’t end there -- zinc is also found in products such as calamine lotion, antiseptics and shampoos. A single dose of any of these is unlikely to cause a problem, but to be on the safe side, avoid using any product containing zinc on your pet.

Symptoms

The signs of zinc poisoning are divided into early- and late-stage symptoms.

In the first instance, a dog suffering from zinc toxicity will likely have a severe tummy ache, sickness, diarrheaand be off his food. Unfortunately, these are quite general signs, but if your dog seems unwell, it is always best to seek veterinary advice.

The late-stage symptoms are subtler because they are linked to things like anemia. This happens because zinc triggers a reaction that makes the body destroy its own red blood cells. Some of the breakdown products of blood appear in the urine to give it a dark-orange or even brown color.

An anemic animallacks the necessary oxygen in his blood to power his organs, and so the dog is tired and lacking in energy. If you lift his lip, instead of the gums looking a healthy pink (just like our own), they look pale or even white.

Causes

To become sick, a dog has to eat, drink or lick a product containing zinc. How sick he becomes depends on factors such as how much he ate, how long it’s been in his stomach and the pH of his stomach acid.

Perhaps the most serious scenario is the stray penny that found its way into a dog’s stomach. Metal objects dissolve slowly over time and so act as a long-term depot of zinc.

The exact mechanism by which zinc does harm is not fully understood, but once absorbed, the zinc circulates in the bloodstream to the organs. In addition to irritating the gut lining and causing organ damage, it causes the body to destroy blood cells and results in anemia.

The video below tells the story of a dog named Penny who nearly died after eating a penny:

Diagnosis

A general blood panel will give clues to the anemia and organ damage. Changes to the red blood cells may strongly suggest the type of damage going on, which is sometimes linked to toxicities.

In addition, analyzing a urine samplecan back up this suspicion, especially if breakdown products of red blood cells are present. This combination helps diagnose hemolytic anemia (meaning the body is damaging itself), but the real trick is to identify the trigger factor -- in this case, zinc. To do this, further tests are necessary.

These include X-rays to seek out metal objects containing zinc and a blood test to measure blood zinc levels. This test usually must be sent away in special blood tubes.

Treatment

The initial treatment is to control sickness and diarrhea and to stop the pet from getting weaker. To these end, medications, including anti-sickness injections, pain relief and gastroprotectants, are used.

If the anemia is severe, then a blood transfusionmay be necessary. If a metallic object is found in the stomach, it needs to be surgically removed; otherwise, it continues to poison the animal.

Zinc already in the bloodstream can be chelated (or bound) and removed with regular subcutaneous injections of calcium disodium EDTA. However, this is not without risk; in the process of leaving the body, the chelated zinc can cause kidney damage.

Prevention

Prevention is better than cure, and in this case, that involves keeping puppies and young animals away from sources of zinc.

References

• “Zinc intoxication in dogs: 19 cases.” Gurnee & Drobatz. JAVMA, 230(8): 1174–1179.
• “Diagnosis and treatment of zinc poisoning in dogs.” Hammond, Loewen & Blakley. Vet Hum Toxicol, 46(5): 272–275.

This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Dec. 17, 2018.