Development and use
Brodifacoum is a second-generation anticoagulant rodenticide (SGAR) that was developed in 1976 and first registered for use in the UK in 1978 (Redfern et al., 1976). While being chemically similar to first-generation anticoagulants like warfarin and coumatetralyl (all are hydroxycoumarins), brodifacoum is classified as an SGAR because it is more potent (i.e. a smaller amount of bait is needed for a kill) and effective against rodents that are resistant to earlier compounds (Hadler and Buckle, 1991). Brodifacoum is registered in all Australian states and territories for controlling introduced rat and mice species.
Mode of action
Brodifacoum exhibits the same mode of action as all anticoagulant rodenticides (Silverman, 1980). When a rodent eats the bait, the active anticoagulant blocks the epoxide reductase enzyme and stops the recycling of activated vitamin K. This severely reduces the production of blood-clotting factors. When the existing supply of clotting factors are eventually degraded, the clotting mechanism fails and haemorrhaging begins. As with all anticoagulants, there is a considerable delay between consumption of a lethal dose and the onset of symptoms. The effects of brodifacoum develop progressively, and include haemorrhage, shock, loss of consciousness and eventual death (Petterino and Paolo, 2001).
Brodifacoum has a very high potency, meaning that it is possible for rodents to consume a lethal dose in a single feed as a fraction of daily food requirement (see Acute poisons). Despite this, brodifacoum is not recommended for use as a single-application rodenticide. Field trials found that for satisfactory control, bait must be available for longer than seven days because some rodents do not feed sufficiently in a single week to acquire a lethal dose (Hadler and Buckle, 1991). Metabolism of brodifacoum occurs very slowly and the compound persists in the liver of rodents, with a half-life of 114–130 days (Fisher et al., 2003) for rats, and 307 days for mice (Vandenbroucke et al., 2008). Excretion of the compound occurs predominantly in the faeces (Laas et al., 1985). Therefore, rodent carcases should be removed from production areas as soon as possible to reduce secondary poisoning risk.
Time to death
- Rats: 3–14 days (Lund, 1981; Saxena and Sharma, 1984; Littin et al., 2000)
- Mice: 3–18 days (Rowe and Bradfield, 1976; Lund, 1981; Newton et al., 1990)
Evidence of resistance
There is little evidence of resistance specific to brodifacoum (MacNicoll et al., 1996). Recent studies indicate that brodifacoum remains effective against warfarin-resistant rodents (Buckle et al., 2012; Meerberg et al., 2014). To date, no resistance studies have been conducted in Australian pest rodent species.
APVMA-registered products containing brodifacoum
Brigand, Ditrac, First Formula, Mortein Mice/Rat Kill Professional, Pest Defence, Pestmaster, Protect-Us Stealth, Protect-Us Verminate, Ratal B, Raticide, Ratsak, Ratshot Red, Rodenthor, Rodex B, RoDi, Surefire, Talon, The Big Cheese, Time’s Up, Tomcat II, Top Cat
NB: All products listed above have a brodifacoum concentration of 0.05g/kg.
Available formulations
- Grain bait
- Pelleted bait
- Paste bait
- Soft bait
- Sachet bait
- Wax block
- Extruded block
Acute toxicity
| Species | LD50 | Average bodyweight | Amount of bait consumed for a LD50 | Reference (for LD50) |
|---|---|---|---|---|
| Mouse | 0.4mg/kg | 20g | 0.16g* | Redfern et al., 1976 |
| Norway rat | 0.49mg/kg | 320g | 3.13g* | FAO, 2015 |
| *Calculated using a bait concentration range of 0.05g/kg | ||||
The table above shows the oral median lethal dose (LD50) values of bromadiolone for the house mouse and Norway rat, the typical bodyweight for an adult animal from each species, and the total amount of commercial bait needed to be eaten to cause death. An adult rat (bodyweight 320 grams) will eat about 20–30 grams of food daily and an adult mouse (bodyweight 20 grams) will eat 2–5 grams of food daily (Hadler and Buckle, 1991). Brodifacoum rodenticides have a standard active concentration of 0.005% (0.05g/kg). Therefore, 3.13 grams of bait would be considered a lethal dose for rats and 0.16 grams of bait is lethal for mice. Because these volumes are within the daily food requirement of target species, it is possible for a lethal dose to be consumed in a single feed.
Poison schedule and regulatory requirements
Brodifacoum is a Schedule 6 poison with a moderate potential for causing harm. Products containing brodifacoum are required to have distinctive packaging with strong warnings and safety directions on the label. There are no special regulations restricting the availability, possession, storage or use of products containing brodifacoum.
Handling, storage and user safety
Wear gloves, safety glasses and appropriate clothing to avoid skin and eye contact. Do not inhale dust. Do not touch the bait. Use the scoop or measure. If on skin and after each baiting, wash thoroughly with soap and water.
Containers that have been used to house bait should not be used for any other purpose. Store in tightly sealed original containers in a dry secure place away from fertilisers, seed, feed and food. Store out of direct sunlight. Keep out of reach of children, unauthorised persons and animals.
Read the label before use. For detailed instructions on handling and user safety, please refer to the relevant Safety Data Sheet.
References
Buckle, A. P., Klemann, N., & Prescott, C. V. (2012). Brodifacoum is effective against Norway rats (Rattus norvegicus) in a tyrosine139cysteine focus of anticoagulant resistance in Westphalia, Germany. Pest management science, 68(12), 1579-1585.
Fisher, P., O’Connor, C., Wright, G., & Eason, C. T. (2003). Persistence of four anticoagulant rodenticides in the livers of laboratory rats. DOC Science Internal Series, 139, 1-19.
Food and Agriculture Organisation of the United Nations. (2015). FAO Specifications and evaluations for agricultural pesticides – brodifacoum. http://www.fao.org/fileadmin/templates/agphome/documents/Pests_Pesticides/Specs/Brodifacoum_2015.pdf
Hadler, M. R., & Buckle, A. P. (1992). Forty-five years of anticoagulant rodenticides—past, present and future trends. In Proceedings of the Fifteenth Vertebrate Pest Conference, 15.
Laas, F. J., Forss, D. A. and Godfreyi, M. E. R. (1985). Retention of brodifacoum in sheep tissues and excretion in faeces. New Zealand journal of agricultural research, 28(3), 357-359.
Littin, K. E., O’Connor, C. E. and Eason, C. T. (2000). Comparative effects of brodifacoum on rats and possums. New Zealand Plant Protection 53:310-315.
Lund, M. (1981). Comparative effect of the three rodenticides warfarin, difenacoum and brodifacoum on eight rodent species in short feeding periods. Epidemiology & Infection, 87(1), 101-107.
MacNicoll, A. D., Kerbms, G. M., Dennis, N. J., & Gill, J. E. (1996). The distribution and significance of anticoagulant-resistant Norway rats (Rattus norvegicus) in England and Wales, 198895. In Proceedings of the Seventeenth Vertebrate Pest Conference, 34. 179-185.
Meerburg, B. G., Bonde, M., Brom, F. W. A., Endepols, S., Jensen, A. N., Leirs, H., Lodal, J., Singleton, G. R., Pelz, H. J., Rodenburg, T. B., and Kijlstra, A. (2004). Towards sustainable management of rodents in organic animal husbandry. NJAS-Wageningen Journal of Life Sciences, 52(2), 195-205.
Newton, I., Wyllie, I. and Freestone, P. 1990. Rodenticides in British barn owls. Environmental Pollution, 68:101-117.
Petterino, C. and Paolo, B. (2001). Toxicology of various anticoagulant rodenticides in animals. Veterinary and Human Toxicology, 43:353-360.
Redfern, R., Gill, J. E. and Hadler, M. R. (1976). Laboratory evaluation of WBA 8119 as a rodenticide for use against warfarin-resistant and non-resistant rats and mice. Journal of Hygiene, 77:419-426.
Rowe, F. P., & Bradfield, A. (1976). Trials of the anticoagulant rodenticide WBA 8119 against confined colonies of warfarin-resistant house mice (Mus musculus L.). Epidemiology & Infection, 77(3), 427-431.
Saxena, Y., & Sharma, R. K. (1984). Efficacy of brodifacoum (Talon) bait against three rodent species. In Proceedings Eleventh Vertebrate Pest Conference, 34.
Silverman, R.B. (1980). A model for the molecular mechanism of anticoagulant activity of 3-substituted 4-hydroxycoumarins. Journal of the American Chemical Society, 102(16), 5421-5423.
Thijssen, H. H. W. (1995). Warfarin-based rodenticides – mode of action and mechanism of resistance. Pesticide Science, 43:73-78.
Vandenbroucke, V., Bousquet-Melou, A., De Backer, P., & Croubels, S. (2008). Pharmacokinetics of eight anticoagulant rodenticides in mice after single oral administration. Journal of veterinary pharmacology and therapeutics, 31(5), 437-445.
