Anticoagulant rodenticides

From Dog

The majority of rodenticide poisonings are caused by anticoagulant rodenticides, which interfere with clotting by inhibiting vitamin K1 epoxide reductase and DT diaphorase. This results in failure to carboxylate clotting factors II, VI, IX and X.

This results in failure to form clots, leading to uncontrollable bleeding.

Anticoagulant rodenticides include brodifacoum, diphacinone (diphenadione) and chlorophacinone.

Clinically affected dogs present with acute depression, lethargy and anorexia. Coagulopathy may present as ventral hematoma formation, muffled heart sounds, pale mucous membranes, epistaxis, hematochezia or gingival bleeding.

In severe toxicity, hemothorax, hemoperitoneum and shock may rapidly ensue, especially with modern synthetic rodenticides such as brodifacoum[1].

Diagnosis is based on history of exposure, presenting clinical signs and coagulation screening tests[2], which usually shows activated clotting time >150 seconds, and prolonged prothrombin and partial thromboplastin times.

A more specific PIVKA test (proteins induced by vitamin K absence or antagonism) may be diagnostically useful for distinguishing anticoagulant poisoning from other coagulopathies. Blood samples showing > 150 seconds for clot formation are usually confirmatory[3].

A differential diagnosis would include congenital clotting factor deficiencies and DIC.

Treatment in severely affected dogs usually requires intravenous fresh frozen plasma or whole blood transfusions.

For outpatients, vitamin K1 is given at 2.5 - 5.0 mg/kg at a single subcutaneous injection, followed by orally once daily for up to 6 weeks.

References

  1. Rickman BH & Gurfield N (2009) Thymic cystic degeneration, pseudoepitheliomatous hyperplasia, and hemorrhage in a dog with brodifacoum toxicosis. Vet Pathol 46(3):449-452
  2. Waddell LS et al (2013) Anticoagulant rodenticide screening in dogs: 123 cases (1996-2003). J Am Vet Med Assoc 242(4):516-521
  3. Mount ME et al (2003) Use of a test for proteins induced by vitamin K absence or antagonism in diagnosis of anticoagulant poisoning in dogs: 325 cases (1987-1997). J Am Vet Med Assoc 222(2):194-198