Thursday, May 16, 2013

What Happens In The Dog's Body With Zinc Toxicity?

by Jennifer Coates, DVM

A West Highland White Terrier named Sierra died last month down the road from me in Denver, CO after eating just one penny. Unfortunately, the dog was in the last throes of zinc toxicosis when she was brought to a veterinary clinic and could not be saved.


At this point you might be confused, thinking, “What do zinc and pennies have to do with each other?” 

In fact, American pennies minted after 1982 (and some produced during that year) are made of 96% zinc, a much cheaper metal than copper. Other potential sources of toxic levels of zinc for dogs include Canadian pennies minted after 1996, galvanized hardware, plumbing supplies, zippers, jewelry, old toys, and zinc-containing sunblock, diaper ointment, and other lotions (e.g., calamine).

Once swallowed, zinc’s first effect is to irritate the lining of the gastrointestinal tract, which can cause vomiting, diarrhea, and a loss of appetite. 

But these are the least of the dog’s concerns. 

Zinc is easily absorbed into the blood stream. This isn’t too surprising since small amounts of zinc, derived from the diet, are essential for normal body function. Even zinc that might appear to be “locked up” in a copper-coated penny or other metallic object will eventually be set free and absorbed by the action of strong acids in the stomach.

When zinc levels reach a critical point, they start to adversely affect red blood cells. 

We don’t know exactly why, but high levels of zinc cause red blood cells to burst through a process called intravascular hemolysis. Severe intravascular hemolysis is devastating for two reasons:
  1. It destroys red blood cells leading to anemia and an inability of the blood to carry sufficient amounts of oxygen.
  2. It releases hemoglobin. Free, circulating hemoglobin (hemoglobinemia) is toxic to tissues.

Anemia and hemoglobinemia can lead to
  • weakness
  • rapid breathing
  • pale and/or yellow mucous membranes and skin
  • dark urine
  • pancreatitis
  • multiple organ failure
  • disseminated intravascular coagulation (an oftentimes fatal condition characterized by blood clotting when it shouldn’t and/or failing to clot when it should)
  • cardiopulmonary arrest

Small dogs, like Westies, are at highest risk for zinc toxicosis.

As Sierra’s case points out, it doesn’t take much zinc to have disastrous consequences on small bodies. Also, coins, bolts, etc. are less likely to get stuck in the stomach of large breed dogs and will pass out of the gastrointestinal tract before much zinc has been absorbed.

Therapy for zinc toxicosis can be successful so long as it is begun before too much damage has been done. When the source of zinc is still present, it must be removed either surgically or with an endoscope. If removal has to be delayed while the patient is stabilized, antacids can be prescribed to decrease stomach acidity and reduce the absorption of more zinc. Blood transfusions and chelation therapy (the use of substances that bind to metals and aid in their elimination from the body) is sometimes necessary in severe cases. Treatment for organ failure and/or disseminated intravascular coagulation may also be necessary. Once the source of zinc is removed, blood zinc levels should return to normal in about two days.

As we all know, some dogs are willing to eat just about anything. Take special care to keep zinc-containing objects out of their reach.

***

Jennifer Coates, DVM graduated with honors from the Virginia-Maryland Regional College of Veterinary Medicine in 1999.  In the years since, she has practiced veterinary medicine in Virginia, Wyoming, and Colorado.  She is the author of several books about veterinary medicine and animal care, including the Dictionary of Veterinary Terms: Vet-speak Deciphered for the Non-veterinarian

Dr. Coates has recently joined the PetMD team and she is now writing for the Fully Vetted column; great blog, do check it out.

Jennifer also writes short stories that focus on the strength and importance of the human-animal bond and freelance articles relating to a variety of animal care and veterinary topics.  Dr. Coates lives in Fort Collins, Colorado with her husband, daughter, and pets.


Articles by Dr. Coates:
Kidney Disease – Say What? 
What Happens In The Dog's Body When The Kidneys Fail To Function Properly? 
Heat Stroke: What Happens In The Dog's Body?  
The Perplexities of Pancreatitis
The Other Side Of The Coin: The Cost Of Defensive Medicine
To Neuter Or Not To Neuter… That Is The Question
Don’t Forget the Physical Therapy
Common Misdiagnoses (Part 1)
Common Misdiagnoses (Part 2)
Picking the Right Dog to Breed
When Is It An Emergency?
Dog Allergies: Common, Commonly Misdiagnosed, or Both? 
Why Does The Spleen Get No Respect?
Protect Your Dog From Snake Bites 
More Creepy Crawlies
Why I Dislike Inflammatory Bowel Disease
Salmonella – A Significant Problem, Or Not? 
What’s In the Vomit?
Cortisol: What Happens In A Dog’s Body When It Goes Awry? 

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