In 1983, the United States government began minting pennies made of zinc wafers coated in copper, rather than just pure copper. This began to cause problems with zinc toxicity in animals that ingested pennies minted after 1983. Other sources of zinc include nuts, bolts, staples, board game pieces, and zinc oxide-based creams.
Zinc toxicity causes a hemolysis, or destruction of red blood cells, causing anemia. Red blood cells carry hemoglobin, a protein necessary for oxygen transfusion in the lungs. Besides the loss of oxygen-carrying capacity due to the decreased red blood cells, the released hemoglobin can be toxic to the kidneys as well. Clinical signs you may see in your pet include lethargy, panting, vomiting, diarrhea, red urine, andicterus (yellow discoloration of skin).
Pennies that are ingested by a dog or cat are much more than simply a foreign object that may cause a gastrointestinal obstruction. If the object is not passing, it should be removed promptly, either surgically or endoscopically by your veterinarian. Advanced cases of zinc toxicity may require other supportive care measures, including fluids, antacids, anti-nausea medications, or possibly blood transfusions.