Difethialone

Difethialone is a potent second-generation anticoagulant rodenticide in the 4-hydroxycoumarin class, used to control rats and mice in urban, agricultural, and commercial settings. It acts by inhibiting vitamin K epoxide reductase, which disrupts recycling of vitamin K and depletes vitamin K–dependent clotting factors II, VII, IX, and X. The resulting coagulopathy leads to uncontrolled bleeding and death. Compared with first-generation anticoagulants, difethialone is more potent and longer-lasting in tissues, enabling delayed effects and reducing the number of feedings required for control, though exposure scenario varies by species.

Used in bait formulations such as pellets, blocks, or liquid baits, it is typically deployed in bait stations to minimize access by children, pets, and wildlife. Efficacy depends on palatability, bait uptake, and the presence of alternative food sources. Regulatory labels emphasize professional use in many jurisdictions and the use of tamper-resistant devices, placement guidelines, and limits on environmental release and secondary exposures.

Non-target and environmental concerns include the risk of secondary poisoning to predators and scavengers that feed on poisoned rodents, as well as potential toxicity to domestic animals and wildlife through direct ingestion or prolonged exposure. Because difethialone can persist in animal tissues, carcass removal is recommended after treatment to reduce secondary risk.

Regulatory status varies by country and region, but many areas classify difethialone as a restricted‑use or professional‑only rodenticide due to its potency and ecological risks.