Zinc phosphide has been used extensively around farms and barns because affected rats tend to die in the open. Toxicity is due to liberation of phosphine gas at the acid pH in the stomach. The gas results in direct GI tract irritation along with cardiovascular collapse. The toxic dose is ~40 mg/kg, and onset is rapid in animals with a full stomach. Clinical signs include vomiting, abdominal pain, and aimless running and howling, followed by depression, dyspnea, and convulsions (which may resemble those seen in strychnine or fluoroacetate poisoning). Death is due to respiratory arrest. The odor of acetylene is present in vomitus or stomach contents. Less frequent lesions include visceral congestion and pulmonary edema. Diagnosis is based on history of exposure to zinc phosphide, suggestive clinical signs, and detection of zinc phosphide in stomach contents. Zinc levels in the blood, liver, and kidneys may be increased. Treatment must include supportive therapy, calcium gluconate, and appropriate fluids to reduce acidosis. Sodium bicarbonate (in cattle, 2–4 L of 5%), PO, to neutralize stomach acidity is recommended.
Last full review/revision March 2012 by Frederick W. Oehme, DVM, PhD