Zinc. You can’t live without it. And, neither can your pets. Like so many things, though, more is not better. Overdosing on zinc can be fatal.
Zinc is an essential metallic micronutrient, meaning our bodies’ requirement for it is extremely small. Zinc is a necessary element in more than 200 enzymes.
SOURCES OF ZINC TOXICOSIS
While it is highly unlikely that a dietary source would cause zinc toxicosis, many non-food sources exist around the home:
• pennies minted after 1982 are the most common toxic source
• zinc-plated and galvanized hardware, including the hardware on pets’ carriers
• ointments, including sunscreen, containing zinc
• acne preparations
• mineral supplements, including multivitamins with minerals
• cold lozenges supplemented with zinc for the immune system
Small-breed dogs and pocket pets (ferrets, birds, hamsters) are overrepresented among domesticated pets suffering zinc toxicosis. This appears to be a dose-related phenomenon. If a small dog (most cats are too fastidious to eat a penny) swallows a penny, the outflow (pylorus) of its stomach may be too small to allow the penny to pass. In the acidic environment of the stomach, a toxic zinc compound is created. So, the longer a penny, nut or bolt stays in the stomach, the more zinc is released and absorbed into the bloodstream. These zinc compounds are highly irritating. Patients vomiting these corrosive concoctions may experience damage to the esophagus and gums. If the toxic mix is aspirated into the respiratory tract, the trachea will be damaged. Pancreatitis can also occur as the irritating brew flows out of the stomach and retrograde into the ducts of the pancreas.
WHAT WILL PET OWNERS SEE?
It may take days before a dog exhibits signs of excessive zinc ingestion and severity of signs will be generally proportional to the amount of zinc ingested. The first sign(s) you might notice could be:
• loss of appetite
• diarrhea, with or without blood (from the irritation of the lining of the stomach and intestine)
• darkly discolored urine
• pale gums and skin
• fast heartbeat
• excessive thirst and urination
WHAT WILL YOUR PET’S DOCTOR SEE?
Ingestion of a tube of zinc-containing cream is more likely to cause acute-onset of symptoms, including vomiting, whereas licking small amounts of zinc-rich ointment from a treated surface (the pet’s skin, or your skin) is more likely to cause a slow onset of symptoms.
By far, hemolysis, the breakdown of red blood cells (RBCs), is the most common clinical finding. Hemolysis can imitate immune-mediated hemolytic anemia (IMHA or AIHA). Thus, your pet’s doctor may want to obtain radiographs (X-rays) of your pet to determine whether he has ingested zinc-containing metal objects, even if IMHA is his primary differential diagnosis.
Other important clinical signs to take note of include:
• renal failure
• evidence of toxicity to the central nervous system (CNS)
TREATMENT OF ZINC TOXICOSIS
How much zinc is lethal for a dog? That study has not been done, and probably never will be. Clinical pathologists, however, have established that the normal zinc concentration in serum should be between 0.7 and 2.0 micrograms/ml.
When possible, removal of the zinc source is the primary therapeutic step. Coins and hardware may be removed from the stomach via endoscope. Items that have moved into the intestine may require laparotomy.
Other treatment is primarily supportive. Fluid administration, at rates up to two times maintenance levels, will help to diurese the patient, relieve damaged kidneys and remove waste products.
Blood products can help. Anemia can be improved by red blood cell administration. Plasma ingredients can help improve protein balance in the serum as well as quell pancreatitis.
Acid controllers can be administered by injection to control gastric inflammation.
Pain medications are indicated for pancreatitis patients and those with esophageal and oral inflammation.
Chelation therapy is controversial in zinc toxicosis. Chelation is the use of chemical ingredients to latch onto minerals and metals and speed their removal from the body. While chelation can improve renal excretion of zinc, it also speeds intestinal absorption.
The best possible outcome in zinc poisoning cases occurs when the pet owner recognizes a source of zinc ingestion and makes the clinician aware of that as a possible cause of a pet’s illness. If you have seen your pet licking a therapeutic ointment or playing with coins or hardware, be sure to mention it to your veterinarian.
See you next week, Dr. Randolph.