Imidacloprid
Imidacloprid was the first commercialized member of a new class of insecticides called chloronicotinyl nitroguanidines or neonicotinoids. First synthesized in its active form by Bayer HealthCare in Japan in 1986, it was developed for control of a variety of insects for both agricultural and veterinary purposes.
A novel 10% spot-on formulation of imidacloprid, Advantage, has been available for the control of fleas on dogs and cats since 1996. Due to its rapid and highly effective activity against fleas and favorable safety profile, imidacloprid has proven to be a remarkable advancement in flea control for pets.
Chemical Properties
Imidacloprid belongs to the neonicotinoid class of insecticides, a relatively new group of the heterocyclic nitromethylenes. The chemical structure and physicochemical properties are listed below (Fig.1, Table 1).
Fig.1: Imidacloprid – chemical structure
Table 1: Physicochemical Properties of Imidacloprid | |
Empirical formula | C9H10ClN5O2 |
Molecular weight | 255.7 |
Physical appearance | cream coloured, crystalline powder |
Melting point | 144°C |
Solubility at 20°C (g/1000 ml) | water: 0.61 |
Vapour pressure | 4 x 10-12 hPa at 20°C |
Mode of Action
Fig.2: Site of action of Imidacloprid on insect nerves
Imidacloprid acts as an agonist on the postsynaptic nicotinic acetylcholine receptors of motor neurones in insects (Fig.2). This causes an over-stimulation of the nervous system, and ultimately kills the insect1.
Following topical application, imidacloprid localises in the water-resistant lipid layer of the skin surface. Fleas do not need to bite an animal in order to be exposed to imidacloprid; rather, it is absorbed through the flea’s non-sclerotised intersegmental membranes2.
Distribution of imidacloprid after topical application
Imidacloprid is spread over the skin surface and throughout the hair coat of dogs and fur of cats within twelve hours after topical application. Due to the greater surface area of larger dogs, application at multiple spots maximizes the translocation and coverage of imidacloprid
Spectrum of Activity
Based on its favorable profile in mammals, imidacloprid was developed for veterinary use and is widely used for flea control in companion animals. The target ectoparasites include various species of fleas (Ctenocephalides spp.), as well as biting (Trichodectes canis) and sucking (Linognathus setosus) lice3. Imidacloprid is registered for use in dogs and cats throughout the world, as well as for rabbits in some countries.
In addition to rapid and potent adulticidal activity against fleas present on dogs and cats, imidacloprid has been shown to have significant flea larvicidal activity, both in laboratory studies as well as in simulated home environments4, 5. This is important as immature stages present in the pets’ surroundings are a reservoir of reinfestation.
Flea larvae in the pet’s surroundings are killed after contact with a pet treated with imidacloprid. Exposure of larvae to these minute quantities of imidacloprid in the environment of treated pets results in marked reduction of developing flea populations in comparison to environments of untreated animals. In this way, it is probable that the larvicidal effects of imidacloprid are of practical significance in breaking the flea life cycle and in reducing the level of flea infestation in the domestic environment6.
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1 also known as French Heartworm
2 Registration for A.vasorum in Europe only
3 In th US, Advantage Multi Dog is not approved for Otodectes, Sarcoptes nor Demodex mites.
5 Registration for lice in Europe, Australia and New Zealand.
Toxicology
Imidacloprid has highly selective binding affinity for insect nicotinic acetylcholine receptors, as well as the fact that insects have much higher numbers of these receptors than vertebrate species. Therefore, the compound is very well tolerated by mammals.
Results of acute toxicological studies in laboratory animals (Table 2) support the low mammalian toxicity, especially when one considers the dermal route of application used in companion animals. Additionally, imidacloprid has been demonstrated to be non-carcinogenic, non-mutagenic and non-teratogenic in numerous laboratory evaluations.
| Table 2: Toxicological data for Imidacloprid | ||
| Toxicological test | Dosage | |
| Rat (unfed), oral | LD50 | 424 - 475 mg/kg |
| Mouse, oral | LD50 | 131 - 168 mg/kg |
| Rat, dermal | LD50 | > 5000 mg/kg |
| Rat, inhalation, aerosol | LC50, 4 hours | > 69 mg/m3 |
| Rat, inhalation, dust | LC50, 4 hours | > 5323 mg/m3 |
| Rat (male/female), subacute | LC50 | > 2400 ppm |
LD50 = dosage resulting in 50% mortality in treatment group.
LC50 = concentration producing 50% mortality in the treatment group.
Questions about the product?
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References
- Krämer, F. and Mencke, N. "Flea Biology and Control: the biology of the cat flea,control and prevention with imidacloprid in small animals". Springer-Verlag, Berlin, Heidelberg, New York (2001).
- Mehlhorn,H., Mencke. N., Hansen,O. "Effects of imidacloprid on adult and larval stages ofthe flea Ctenocephalides felis after in vivo and in vitro application: a light- and electron-microscopy study". Parasitol Res (1999) 85: 625 – 637.
- Hanson I, Mencke N, Asskildt H, Ewald-Hamm D, Dorn H. Field study on the insecticidal efficacy of Advantage against natural infestations of dogs with lice. Parasitol Res 85:347-348, 1999.
- Hopkins TJ, Woodley I, Gyr P. Imidacloprid topical formulation: larvicidal effect against Ctenocephalides felis in the surroundings of treated dogs. Aust Vet Pract 26:210, 1996.
- Jacobs DE, Hutchison MJ, Stanneck D, et al. Accumulation and persistence of flea larvicidal activity in the immediate environment of cats treated with imidacloprid. Med Vet Entomol 15:342-345, 2001.
- Jacobs DE, Hutchison MJ, Ewald-Hamm D. Inhibition of immature Ctenocephalides felis felis (Siphonaptera: Pulicidae) development in the imediate environment of cats treated with imidacloprid. J Med Entomol 37:228-230.