Brodifacoum

Brodifacoum is a highly lethal anticoagulant poison. In recent years, it has become one of the world's most widely used pesticides. It is typically used as a rodenticide but is also used to control rabbits, possums and other mammalian pests^[1].

Brodifacoum, like most anticoagulant poisons, has the advantage that one of its first effects is dehydration, forcing the rodent to move away from human habitation in search of water. As such, there is less chance that homeowners will be forced to deal with decomposing remains inside their building. Dehydrated bodies also dry out more readily, possibly leaving an odorless, mummified carcass.

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Toxicology

Brodifacoum has a similar mode of action to warfarin. However due to very high potency and long duration of action (elimination half-life of 20 – 130 days), it is characterised as a "second generation" or "superwarfarin" anticoagulant.^[2]

Brodifacoum inhibits the enzyme Vitamin K epoxide reductase. This enzyme is needed for the reconstitution of the vitamin K in its cycle from vitamin K-epoxide, and so brodifacoum steadily decreases the level of active vitamin K in the blood. Vitamin K is required for the synthesis of important substances including prothrombin, which is involved in blood clotting. This disruption becomes increasingly severe until the blood effectively loses any ability to clot.

In addition, brodifacoum (as with other anticoagulants in toxic doses) increases permeability of blood capillaries; the blood plasma and blood itself begins to leak from the smallest blood vessels. A poisoned animal will suffer progressively worsening internal bleeding, leading to shock, loss of consciousness, and eventually death.

Brodifacoum is highly lethal to mammals and birds, and extremely lethal to fish. It is a highly cumulative poison, due to its high lipophilicity and extremely slow elimination.

Following are acute LD₅₀ values for various animals (mammals)^[3]:

• rats (oral) 0.27—0.30 mg/kg b.w.
• mice (oral) 0.40 mg/kg b.w.
• rabbits (oral) 0.30 mg/kg b.w.
• guinea-pigs (oral) 0.28 mg/kg b.w.
• cats (oral) 0.25 mg/kg b.w.
• dogs (oral) 0.25 mg/kg b.w.

LD₅₀ values for various birds varies from about 1 mg/kg b.w. — 20 mg/kg b.w.^[4].

LC₅₀ (concentration prone of killing 50% of animals exposed to it) for fish:

• trout (96 hours exposure) 0.04 ppm^[5]

Given these extremely high toxicities in various mammals, brodifacoum is classified as "extremely toxic" (LD₅₀ < 1.0 mg/kg b.w.) and "very toxic" (T+; LD₅₀ < 25 mg/kg b.w.), respectively. Because of its persistency, cumulative potential and high toxicities for various wildlife species, it is also considered an environmental pollutant (N; noxious to the environment). The readiness of brodifacoum to penetrate intact skin should be noted, and brodifacoum and commercial preparations containing it should be handled with respective care and precaution because of its skin resorptivity.

The estimated average fatal dose for an adult man (60 kg b.w.) is about 15 mg, without treatment^[6]. However, due to low bait concentrations (usually 10 — 50 mg/kg bait, i.e. 0.001 — 0.005%) and slow onset of symptoms, and the existence of a highly effective antidote (appropriately dosed vitamin K₁), brodifacoum is considered to be of relatively low hazard to humans.

Brand names

Brodifacoum is marketed under a large variety of trade names, including d-Con, Finale, Fologorat, Havoc, Jaguar, Klerat, Matikus, Mouser, Pestoff, Ratak+, Rodend, Talon, Volak and Volid.

Treatment

The primary antidote to brodifacoum poisoning is immediate administration of vitamin K₁ (initially slow intravenous injections of 10-25 mg repeated all 3–6 hours until normalisation of the prothrombin time; then 10 mg orally four times daily as a "maintenance dose"). It is an extremely effective antidote, provided the poisoning is caught before too much damage has been done to the victim's circulatory system. As high doses of brodifacoum can affect the body for many months, the antidote must be administered regularly for a long period with frequent monitoring of the prothrombin time.

If unabsorbed poison is still in the digestive system, gastric lavage followed by administration of activated charcoal may be required.

Further treatments to be considered include infusion of blood or plasma to counteract hypovolemic shock; and in severe cases, infusion of blood clotting factor concentrate.

Administration of vitamin C is also recommended (100 mg three times daily)^[7].

Another potential treatment is phenobarbital, which is believed to accelerate the metabolism of some anticoagulants via enzyme induction.

Poisoning case reports

There have been at least ten case reports of brodifacoum intoxication in the medical literature.

In one report^[8], a woman deliberately consumed over 1.5 kilograms of rat bait, constituting about 75 mg brodifacoum, but made a full recovery after receiving conventional medical treatment.

In another report^[9], a 17-year-old boy presented to the hospital with a severe bleeding disorder. It was discovered that he habitually smoked a mixture of brodifacoum and marijuana. Despite treatment with vitamin K, the bleeding disorder persisted for several months. He eventually recovered.

Notes

1. ^ Eason, C.T. and Wickstrom, M. Vertebrate pesticide toxicology manual, New Zealand Department of Conservation
2. ^ http://www.inchem.org/documents/hsg/hsg/hsg093.htm
3. ^ http://www.inchem.org/documents/pds/pds/pest57_e.htm
4. ^ http://www.inchem.org/documents/hsg/hsg/hsg093.htm
5. ^ http://www.wil-kil.com/public/2005-06_labels-msds/WeatherBlok%20XT%20M.pdf#search=%22LC50%2Bbrodifacoum%22
6. ^ http://www.inchem.org/documents/hsg/hsg/hsg093.htm
7. ^ http://www.inchem.org/documents/pds/pds/pest57_e.htm
8. ^ Lipton, R.A. & Klass, E.M. (1984) Human ingestion of a 'superwarfarin' rodenticide resulting in a prolonged anticoagulant effect. JAMA 252:3004-3005.
9. ^ La Rosa, F, Clarke, S. & Lefkowitz, J. B. (1997) Brodifacoum intoxication with marijuana smoking. Archives of Pathology & Laboratory Medicine 121:67-69.

New England Journal of Medicine, vol 356, no. 2, Jan. 11, 2007 Case Records of the Massachusetts General Hospital (a near fatal case of brodifacoum poisoning).[1]

Further reading

• Tasheva, M. (1995). Environmental Health Criteria 175: Anticoagulant rodenticides. World Health Organisation: Geneva.