Fipronil is an insecticide and acaricide from the phenylpyrazole family. It acts by inhibiting the GABA complex, binding to the chloride channel and thereby blocking pre and post-synaptic transfer of chloride ions across the membrane. This results in uncontrolled activity of the central nervous system and death in insects and acarids. Fipronil exhibits insecticidal and acaricidal activity against fleas (Ctenocephalides spp.), ticks (Ixodes spp.) and lice (Trichodectes canis and Felicola subrostratus) in dogs and cats.

*Absorption – The amount of Fipronil absorbed by the skin in the dog, after application of the spray to the coat and skin is extremely slight to negligible.*Distribution – The persistence of fipronil on the hair is very long (on average 52.5 ± 11.5 days), given that the limit of quantification of the assay method is 0.25 µg/g. This can be explained by the fact that fipronil dissolves well in fat and concentrates in the sebaceous glands. From the sebaceous glands the amount of fipronil on the skin is constantly replenished.*Biotransformation – In all species fipronil is mainly metabolised to its sulphone derivative (RM1602), which also possesses insecticidal and acaricidal properties.The RM1602 detected on the hair after spray application in dogs may be explained by its presence in the original raw material.