Development and use
Flocoumafen is a second-generation rodenticide that was first synthesised in 1984 (Bowler et al., 1984). 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 required for a kill) and effective against rodents resistant to earlier compounds (Hadler and Buckle, 1991). Flocoumafen has been used around the world, most notably for controlling rats in rice fields in the Philippines (Hoque and Olvida, 1988). In Australia, flocoumafen is registered in all states for controlling introduced rats and mice, especially warfarin-resistant strains.
Mode of action
Flocoumafen 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, and 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 and the onset of symptoms. The effects of flocoumafen develop progressively and include haemorrhage, shock, loss of consciousness and eventual death (Petterino and Paolo, 2001).
Flocoumafen is highly potent. 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, it is not recommended for use as a single-application rodenticide. Users are advised to re-apply bait weekly for several weeks to allow rodents to feed sufficiently to acquire a lethal dose (Hadler and Buckle, 1991). Flocoumafen is not metabolised well by rodents and is mainly excreted through faeces (Huckle et al., 1988). Flocoumafen is highly persistent in rodent liver tissue, with a half-life of 220 days for rats and 94 days for mice (Huckle et al., 1988; Vandenbroucke et al., 2008). Therefore, rodent carcases should be removed from production areas as soon as possible to reduce secondary poisoning risk.
Time to death
- Rats: 3–11 days (Rowe et al., 1985; Lund, 1988)
- Mice: 4–19 days (Bowler et al., 1984; Parshad and Chopra, 1986; Lund, 1988)
Evidence of resistance
There is little evidence of resistance to flocoumafen (Bowler et al., 1984; Rowe et al., 1985; MacNicoll et al., 1996) or reduced efficacy against warfarin-resistant strains (Meerberg et al., 2014). To date, no resistance studies have been conducted on Australian pest rodent species.
Australian-registered manufacturers/products
Storm (0.05g/kg), Stratagem (0.05g/kg)
Available formulation
- Bait concentrate
- Extruded bait
- Grain bait
- Pellet bait
- Wax block
Acute toxicity
| Species | LD50 | Average bodyweight | Amount of bait consumed for a LD50 | Reference (for LD50) |
|---|---|---|---|---|
| Mouse | 0.79–2.4mg/kg | 20g | 0.4–1g* | Bowler et al., 1984 |
| Norway rat | 0.25–0.56mg/kg | 320g | 1.6–3.6g* | Bowler et al., 1984 |
| *Calculated using a bait concentration of 0.05g/kg | ||||
The table above shows the oral median lethal dose (LD50) values of flocoumafen 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). Flocoumafen rodenticides have a standard active concentration of 0.005% (0.05g/kg). Therefore, 1.6–3.6 grams of bait would be considered a lethal dose for rats and 0.4–1 grams 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
Flocoumafen is a Schedule 6 poison with a moderate potential for causing harm. Products containing flocoumafen 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 flocoumafen.
Handling, storage and user safety
Segregate from foods and animal feed. Protect from temperatures above 30°C. Protect against moisture. Protect from direct sunlight.
Do not apply baits in the open; they should be covered or placed in secure boxes. When using, do not eat, drink or smoke. Ensure ventilation of stores and work areas. Thoroughly wash hands after handling.
Read the label before use. For detailed instructions on handling and user safety, please refer to the relevant Safety Data Sheet for the product.
References
Bowler, D. J., Entwistle I.D., and Porter, A.J. (1984). WL 108366 – a potential new rodenticide. In Proceedings of the British crop protection conference on pests and diseases.
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.
Hoque, M. M. and Olvida, J. L. (1988). Efficacy and environmental impact of flocoumafen (Storm) wax block baits used for rice field rat control in the Philippines. Proceedings of the Thirteenth Vertebrate Pest Conference, 16.
Huckle, K. R., Hutson, D. H. and Warburton, P. A. (1988). Elimination and accumulation of the rodenticide Flocoumafen in rats following repeated oral administration. Xenobiotica, 18:1465-1479.
Lund, M. (1988). Flocoumafen – a new anticoagulant rodenticide. In Proceedings of the Thirteenth Vertebrate Pest Conference, 13.
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., Van Gent‐Pelzer, M. P., Schoelitsz, B., and Van Der Lee, T. A. (2014). Distribution of anticoagulant rodenticide resistance in Rattus norvegicus in the Netherlands according to Vkorc1 mutations. Pest management science, 70(11), 1761-1766.
Parshad, V. R., & Chopra, G. (1986). The susceptibility of Rattus rattus and Bandicota bengalensis to a new anticoagulant rodenticide, flocoumafen. Epidemiology & Infection, 96(3), 475-478.
Petterino, C. and Paolo, B. (2001). Toxicology of various anticoagulant rodenticides in animals. Veterinary and Human Toxicology, 43:353-360.
Rowe, F. P., Bradfield, A., and Swinney, T. (1985). Pen and field trials of a new anticoagulant rodenticide flocoumafen against the house mouse (Mus musculus L.). Epidemiology & Infection, 95(3), 623-627.
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.
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.
