SKIN DISTRIBUTION OF FIPRONIL BY MICROAUTORADIOGRAPHY FOLLOWING TOPICAL ADMINISTRATION TO THE BEAGLE DOG

To investigate the localisation of fipronil in dog skin, [C-14]-fipron il was topically applied to a male beagle dog (spot-on administration) at the therapeutic dose of 10 mg/kg. By means of autohistoradiography , the radioactivity was precisely detected in the skin and appendages at various intervals after application. Radioactivity was predominantl y observed within the stratum corneum, the viable epidermis, and in th e pilo-sebaceous units (mainly in the sebaceous glands and epithelial layers). [C-14]-fipronil was significantly detected in these structure s up to 56 days post-treatment, in the application zone (neck) but als o in the lumbar zone, thus indicating the mechanical displacement of f ipronil. No radioactivity was detected in either the dermal or the hyp odermal layers, confirming the low percutaneous passage of fipronil.