Is Zinc phosphide safe for dogs and cats?

Zinc phosphide (Zn₃P₂) is a highly toxic rodenticide/gopher/mole control agent. Mechanism: upon contact with gastric acid or water, zinc phosphide rapidly decomposes to phosphine gas (PH₃) — one of the most acutely toxic gases known. Phosphine inhibits cytochrome c oxidase and complex IV of the mitochondrial electron transport chain → cellular energy failure; also directly damages cardiac, pulmonary, and hepatic tissue. Minimum lethal dose in dogs: approximately 40–60 mg/kg of zinc phosphide (generating approximately 14 mg/kg phosphine). Secondary inhalation hazard: when a poisoned dog vomits, phosphine gas is released — owners and veterinary staff in closed spaces risk inhalation injury from vomit fumes. There is NO specific antidote. Management: vomiting must be induced only in well-ventilated areas (outdoors if possible) with staff avoiding inhalation; activated charcoal; sodium bicarbonate in water may raise gastric pH to slow phosphine release; intensive supportive care (cardiac monitoring, liver/kidney support). Onset of signs: within 1–4 hours of ingestion — vomiting, lethargy, ataxia, hypersalivation, followed by cardiac arrhythmia, pulmonary edema, and collapse. Prognosis is guarded to poor for significant exposures even with intensive treatment.

Cats are susceptible to zinc phosphide toxicosis through direct ingestion of bait products (pellets, tracking powders) and through secondary exposure from ingesting poisoned rodents. Cats' smaller body mass means even small bait quantities can deliver toxic phosphine doses. The mechanism, clinical presentation, and treatment approach are identical to the dog context. The inhalation hazard during management (phosphine released when the animal vomits) is particularly important in veterinary clinic settings where multiple animals and staff may be at risk. Outdoor cats in areas where zinc phosphide is used for pocket gopher, mole, or vole control are at chronic low-level secondary poisoning risk. Because phosphine is colorless and its garlic/fish-like odor may not be detected at dangerous concentrations (olfactory adaptation), the secondary inhalation hazard requires active management protocols.